NOAA Technical Report NOS OCS 15 

_____________________________________________________________________ 

NOS EXPERIMENTAL NOWCAST/FORECAST SYSTEM FOR THE 

PORT OF NEW YORK/NEW JERSEY (NYEFS): REQUIREMENTS, 

OVERVIEW, AND SKILL ASSESSMENT

Eugene Wei 

Manchun Chen 

Silver Spring, Maryland 

October, 2002 

noaa National Oceanic and Atmospheric Administration 

---------------------------------------------------------------------------------- 

U.S. DEPARTMENT OF COMMERCE 

National Ocean Service 

Office of Coast Survey 

Coast Survey Development Laboratory
ii

TABLE OF CONTENTS 

LIST OF FIGURES ........................................................................................................................ ii 

LIST OF TABLES......................................................................................................................... iv 

EXECUTIVE SUMMARY ........................................................................................................... vi 

1. INTRODUCTION .......................................................................................................................1 

2. NEEDS ANALYSIS AND REQUIREMENTS ASSESSMENT................................................5 

3. SYSTEM OVERVIEW .............................................................................................................11 

3.1. Data Ingest and Boundary Forcing Generation .........................................................11 

3.2. Nowcast Run...............................................................................................................13 

3.3. Forecast Run ...............................................................................................................13 

3.4. Operational Environment and Scheduling..................................................................15 

3.5. System Interruption and Recovery Procedure ............................................................15 

4. SEMI-OPERATIONAL NOWCAST/FORECAST SKILL ASSESSMENT ...........................19 

4.1. Analysis Method .........................................................................................................19

4.2. Skill Assessment for Water Level Nowcasts..............................................................20 

4.3. Skill Assessment for Water Level Forecasts ..............................................................23 

4.4. Skill Assessment for Current Nowcasts......................................................................30 

Nowcast Current Speed and Direction Skill Assessment at Bergen Point ............30 

Nowcast Current Slack Time at Bergen Point .......................................................31 

Nowcast Current Speed and Direction at The Narrows.........................................33 

Nowcast Current Slack Time at The Narrows .......................................................34 

Nowcast Maximum Flood and Ebb Currents at The Narrows...............................35 

4.5. Skill Assessment for Current Forecasts ......................................................................36 

Forecast Current Speed and Direction Skill Assessment at Bergen Point.............38 

Forecast Current Slack Time at Bergen Point........................................................38 

Forecast Maximum Flood and Ebb Currents at Bergen Point ...............................39 

Forecast Current Speed and Direction at The Narrows .........................................39 

Forecast Current Slack Time at The Narrows........................................................42 

Forecast Maximum Flood and Ebb Currents at The Narrows ...............................42 

5. SUMMARY...............................................................................................................................44 

ACKNOWLEDGMENT................................................................................................................44 

REFERENCES ..............................................................................................................................45 
iii

LIST OF FIGURES 

Figure 1. Map showing New York Harbor and major tributaries...................................................2 

Figure 2.1. New York Harbor PORTS stations maintained by NOS...............................................5 

Figure 2.2. Water level at Bayonne Bridge; (a) observations and astronomical tide prediction, (b) 

surface wind observations, and (c) over-laid with model water level nowcast and 

forecasts. ..............................................................................................................................6 

Figure 2.3. Parameters and locations that marine pilots need for navigation. ................................7 

Figure 3.1. Schematic of the NYEFS system operation function element. .....................................9 

Figure 3.2. Station locations available for model system water level output. ..............................12 

Figure 3.3. NYEFS nowcast run schedule....................................................................................14 

Figure 3.4. NYEFS forecast run schematic flow chart .................................................................15 

Figure 4.1. Observed and model nowcast water level time series at the Bayonne Bridge, October 

12 - 17, 2000. .....................................................................................................................17 

Figure 4.2. Observed and model nowcast water level time series at The Battery, October 12 - 17, 

2000....................................................................................................................................18 

Figure 4.3. Observed and model forecast water level time series at the Bayonne Bridge, October 

12 - 17, 2000. .....................................................................................................................21 

Figure 4.4. Observed and model forecast water level time series at The Battery, October 12 - 17, 

2000....................................................................................................................................21 

Figure 4.5. Observed and model nowcast current speed time series (low-passed) at Bergen Point, 

October 6 - 11, 2000. .........................................................................................................27 

Figure 4.6. Observed and model nowcast current speed time series (low-passed) at The Narrows, 

August 20 - 23, 2001..........................................................................................................31 

Figure 4.7. Observed and model forecast current speed time series (low-passed) at Bergen Point, 

October 6 - 11, 2000. .........................................................................................................34 
iv

LIST OF TABLES 

Table 4.1. Model system water level nowcast skill assessment standard statistics for complete 

time series at Bayonne Bridge and The Battery. (Note: na = not applicable) ...................18 

Table 4.2. High and low water level nowcast skill assessment standard suite statistics at the 

Bayonne Bridge. (Note: na = not applicable) ....................................................................19 

Table 4.3. High and low water level nowcast skill assessment standard suite statistics at The 

Battery. (Note: na = not applicable)...................................................................................20 

Table 4.4. Model system water level forecast skill assessment standard statistics for complete 

time series (two cycle forecasts) at Bayonne Bridge. (Note: Overall RMSE average: 13.4 

cm.) ....................................................................................................................................22 

Table 4.5. Model system water level forecast skill assessment standard statistics for complete 

time series (two cycle forecasts) at The Battery. (Note: Overall RMSE average: 14.3 cm.)

............................................................................................................................................22 

Table 4.6. MDL water level forecast skill assessment standard statistics at Sandy Hook. (Note: 

Overall RMSE average: 21.6 cm.).....................................................................................23 

Table 4.7. MDL water level forecast skill assessment standard statistics at Sandy Hook after the 

correction. (Note: Overall RMSE average: 13.3 cm) .......................................................23 

Table 4.8. NYEFS water level forecast and astronomical tide prediction skill assessment standard 

suite statistics at the Bayonne Bridge and The Battery. (Note: na = not applicable) ........25 

Table 4.9. High and low water level forecast skill assessment standard suite statistics at Bayonne 

Bridge. (Note: na = not applicable) ...................................................................................26 

Table 4.10. High and low water level forecast skill assessment standard suite statistics at The 

Battery. (Note: na = not applicable)...................................................................................26 

Table 4.11. Nowcast current speed and direction skill assessment standard suite statistics at 

Bergen Point, based on 12,384 six minutes interval data. (Note: na = not applicable) .....28 

Table 4.12. Skill assessment standard suite statistics for begin and end times of SBE (slack 

before ebb) and SBF (slack before flood) differences between current observations (at bin 

8) and nowcastss (at layer 3) at Bergen Point. (Note: na = not applicable).......................29 

Table 4.13. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 8) and nowcast currents (in 

layer 3) at Bergen Point. (Note: na = not applicable) ........................................................29 

Table 4.14. Current speed and direction nowcast skill assessment standard suite statistics at The 

Narrows, based on 18,985 six minutes interval data. (Note: na = not applicable) ............31 

Table 4.15. Skill assessment standard suite statistics for begin and end times of SBE (slack 

before ebb) and SBF (slack before flood) differences between current observations (at bin 

20) and forecasts (at layer 2) at The Narrows. (Note: na = not applicable).......................32 

Table 4.16. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 20) and nowcasts (in layer 2) 

at The Narrows. (Note: na = not applicable)......................................................................33 

Table 4.17. Forecast current speed and direction skill assessment standard suite statistics at 

Bergen Point, based on 11,674 six minutes interval data. (Note: na = not applicable) .....34 

Table 4.18. Model system current speed forecast statistics at each of 24 projection hour at 

Bergen Point. (Note: Overall RMSE average: 29 cm.s-1).................................................35 

Table 4.19. Model system current direction forecast statistics at each of 24 projection hour at 

Bergen Point. (Note: Overall RMSE average: 20.0 degrees) ...........................................35 

Table 4.20. Skill assessment standard suite statistics for begin and end times of SBE (slack 
v

before ebb) and SBF (slack before flood) differences between current observations (at bin 

20) and forecasts (at layer 2) at Bergen Point. (Note: na = not applicable).......................36 

Table 4.21. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (bin 20) and forecasts (layer 2) at 

Bergen Point. (Note: na = not applicable) .........................................................................37 

Table 4.22. Current speed and direction forecast skill assessment standard suite statistics at The 

Narrows, based on 18,935 six minutes interval data. (Note: na = not applicable) ............38 

Table 4.23. Model system current speed forecast statistics at each of 24 projection hour at The 

Narrows. (Note: Overall RMSE average: 13 cm.s-1) ........................................................39 

Table 4.24. Model system current direction forecast statistics at each of 24 projection hour at The 

Narrows. (Note: Overall RMSE average: 24.1 degrees)...................................................39 

Table 4.26. Skill assessment standard suite statistics for begin and end times of SBE (slack 

before ebb) and SBF (slack before flood) differences between current observations (at bin 

20) and forecasts (at layer 2) at The Narrows. (Note: na = not applicable).......................40 

Table 4.27. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 20) and forecasts (in layer 2) 

at The Narrows. (Note: na = not applicable)......................................................................41 
vi

EXECUTIVE SUMMARY 

This document describes the Port of New York/New Jersey Water Level and Current 

Experimental Model Forecast System and an assessment of its skill. The system, based on a 

hydrodynamic model, uses near real-time and oceanographic and atmospheric observations and 

forecasts to produce water level and current nowcasts and forecasts throughout the entire model 

domain which includes New York Harbor and its estuarine vicinity. In addition to the near realtime information and astronomical tide predictions at a number of gauge locations, the mariners 

navigating in the Harbor can access the model system generated information to improve 

navigational safety and to optimize cargo operations. 

The needs for developing such a model system are analyzed and the model system requirements 

are also assessed based on a survey of local maritime pilots. The model system structures and 

operational procedures are described in this document. 

The model system skill assessment scenarios specified by NOS (1999) include the astronomical 

tide simulation, the model system test nowcasts and forecasts, and the pseudo-operational 

nowcasts and forecast. The primary statistics used to assess the model performance include: the 

Central Frequency (CF) - to measure the model errors from a specified target; the Positive 

Outlier Frequency (POF) and Negative Outlier Frequency - to describe how often the model 

system either over or under predicts; Maximum Duration of Positive Outliers (MDPO) and 

Maximum Duration of Negative Outliers (MDNO) - to describe how long the model system 

either over or under predicts. The skill assessment of the astronomical tide simulation and the 

model hindcasts (in place of test nowcasts/forecasts) are described in Wei and Chen (2001). The 

results from the experimental model system nowcast/forecast are summarized as follows. 

(1) Water Level at Bayonne and The Battery 

Nowcasts: All statistics meet NOS (1999) standard 

Forecasts: Do not meet NOS (1999) but better than astronomical tide predictions 

Bayonne Bridge: CF > 80%, POF and NOF about 1% to hour 6 

 CF about 75% at hour 24 and POF and NOF about 2%. 

The Battery: CF about 75%, POF < 1%, NOF about 3% to hour 6 

 CF about 71%, POF about 1%, NOF about 3% to hour 24 

(2) Currents 

Nowcasts: Do not meet NOS (1999) at Bergen Point. Meet NOS (1999) at The Narrows 

Bergen Point: Speed: CF(76%), POF(9%), NOF(0%), MDPO & MDNO < 3 hours 

 Direction: CF(86%), POF & NOF < 1%, MDPO & MDNO < 1 hour 

The Narrows: Speed: CF(95%), POF & NOF< 1%, MDPO & MDNO < 3 hours 

 Direction: CF(94%), POF(2.5%), NOF<1%, MDPO & MDNO < 15 hours 

Forecasts: 

Bergen Point: Speed: CF(76%), POF(9%), NOF(0%), MDPO & MDNO < 22 hours 

 Direction: CF(85%), POF & NOF < 1%, MDPO & MDNO < 8 hours 

The Narrows: Speed: CF(95%), POF & NOF< 1%, MDPO & MDNO < 2 hour 

 Direction: CF(94%), POF(2%), NOF < 1%, MDPO & MDNO < 14 hours
1. INTRODUCTION

Mariners navigating in New York Harbor (Figure 1) and nearby estuaries rely on astronomical 

tide predictions (NOS Tide and Tidal Current Tables) and real-time water level and current 

information (PORTS - Physical Oceanographic Real-Time System) at selected locations 

maintained by National Ocean Service (NOS) of NOAA. However, these gauges provide limited 

information to the users and the astronomical tide predictions do not account for the non-tidal 

signals induced either by meteorological or river discharge influences. 

A numerical model-based forecast system is the most effective and accurate tool to account for 

the effects of the non-tidal signals on the water levels and currents in the harbor. The Port of 

New York/New Jersey Experimental Forecast Model System (NYEFS) is designed to provide 

accurate water level and current predictions to the marine community in the New York Harbor 

region (Figure 1.1). The needs and requirements for developing the system as a forecast 

component of NOS=s PORTS are described in Chapter 2. 

The model system includes a hydrodynamic model component and a suit of software for 

processing input and output data, including graphic applications. The nowcast/forecast model 

system operation consists of three components: input data ingest, model nowcast/forecast, and 

model data post-processing. Each element is controlled by automated scripts on a Unix 

environment. The sequential procedures include: gathering and formatting the input data for the 

hydrodynamic nowcast/forecast simulations, running the nowcast/forecast model, and postprocessing the model output to graphically display on the Internet or for dissemination to users 

via ftp. The system overview is described in Chapter 3. 

The hydrodynamic model of the experimental nowcast/forecast model system has been 

developed and calibrated (Wei and Chen, 2001) based on a three-dimensional barotropic version 

of the Princeton Ocean Model (POM, Blumberg and Mellor, 1987). A fine sub-grid model, 

covering channels and bays critical to navigation, including the Kill van Kull and Bergen Point, 

has been developed and embedded within and dynamically connected to the coarse grid model 

using a one-way coupling technique. Figure 1.2 shows the model grids. The model system 

provides hourly nowcasts and 36 hour forecasts of water levels and currents within the New 

York Harbor. 

Since April of 1999, the experimental system has been implemented and run on NOS=s Coastal 

Survey Development Laboratory (CSDL) computer. The model system has been modified to 

improve the accuracy and reliability. Automated scripts handling operational procedures have 

been modified and updated to accommodate a variety of networking and changes in data types. 

This report describes the model performance based on NOS requirements for operational 

nowcast/forecast system (NOS, 1999). Skill assessments for tidal simulation and test nowcast 

assessments have been reported as part of the model documentation in Wei and Chen (2001). 

Due to 1997 observed data errors at The Battery, the water level test nowcast skill assessment at 

The Battery was based on four months of observations. A test nowcast simulation conducted 

using the entire1998 data shows similar results to the 1997 four month test nowcast skill 
assessment. Model nowcast/forecast output from the experimental system are saved for skill 

assessment, which is presented in Chapter 4. This report, in conjunction with the model 

documentation (Wei and Chen, 2001), completes the Port of New York/New Jersey skill 

assessment required by NOS (1999). 

Figure 1. Map showing New York Harbor and major tributaries.
2. NEEDS ANALYSIS AND REQUIREMENTS ASSESSMENT

Much of the hydrodynamics in the harbor are determined by the coastal fluctuations propagating 

through the harbor entrance (Figure 1.1). The main flow goes through The Narrows; part of the 

flow north of The Narrows goes to the East River and the Kill van Kull, while the reminder goes 

to the Hudson River. When the flow through the Kill van Kull meets the flow through the 

Arthur Kill at Bergen Point, a tidal eddy is generated. The flow continues north to the Upper 

Newark Bay. 

In the Harbor, NOS maintains a PORTS for navigation safety. Information provided to the users 

by NY PORTS includes: water level at Sandy Hook, Kings Point, The Battery, and Bayonne 

Bridge; meteorology at Robbins Reef, Bayonne Bridge Sandy Hook, and Kings Point; and 

currents at Bergen Point and The Narrows (Figure 2.1). 

NOS=s PORTS provides near real-time information to users only at the gauge stations. However, 

there is still need for information in addition to the near real-time information at PORTS stations, 

including: 

(1) near real-time water level and current information at non-gauge locations, 

(2) short term (1 to 2 days) water level and current forecast guidance information, and 

(3) detailed current information in navigational channels, such as the Kill van Kull, for Coast 

Guard Aright of way@ decision making. 

Figure 2.2(a) shows a water level time series at Bayonne Bridge from January 11 to 16, 2002. 

On January 13, due to a strong westerly wind (Figure 2.2(b)), the observed water levels (asterisks) 

dropped from 0.5 m above the astronomical tide prediction (solid line) to 0.8 m below the 

astronomical tide prediction within 24 hours. The situation poses a groundin grisk. Therefore, 

for navigation safety, there is the need for a more accurate tool other than just the astronomical 

prediction. The Port of New York/New Jersey Experimental Water Level and Current 

Nowcast/Forecast Model System is designed for this purpose. Figure 2.2(c) shows the model 

system water level nowcast and forecast for the same period. Both the model nowcast (dotted 

line) and the forecast (dashed line) are much closer to the observations than just the astronomical 

tide predictions. This example shows that an oceanographic forecast system based on a 

hydrodynamic model is an effective tool to make near real-time nowcasts and short term 

forecasts of the water levels and currents in an estuary. 

Marine pilots of the Port of New York and New Jersey maritime community such as the Sandy 

Hook Pilot Association have participated in activities of the Harbor Navigation Committee 

organized by the Port Authority of New York & New Jersey. Through this Committee, 

representatives from NOS=s Office of Coast Survey have collected the oceanographic 

information needs voiced by the marine pilots and other users. In May, 2001, a user needs and 

requirements questionnaire was distributed to the maritime community for information. The 

questionnaires, designed by CSDL, requested users to identify their priorities for oceanographic 

parameters (water level, current, salinity, and temperature), the information on necessary 

locations; and the information on frequency and error tolerance.
The results from returned questionnaires are summarized as follows: 

(1) The oceanographic parameters of highest priority are the water level and current nowcasts 

and forecasts. 

(2) The locations of high priority are shown in Figure 2.3. In response to the survey, NOS 

deployed a current meter at The Narrows in August, 2001 as part of the NY PORTS. 

(3) The forecast information should be at least out to 24 hours. 

(4) The forecast information report frequency should be at least hourly or shorter. 

(5) The forecast information should be updated at least four times a day. 

(6) The nowcast and forecast error tolerance proposed by NOS (1999) for water level and current 

speed are acceptable (e.g., 90% of the time the errors be less than 0.5 ft for water level and 

0.5 kt for current speed). 

(7) A 95% confidence limit is recommended. 

(8) Dissemination methods requested include web-based time series plot, plan views, and 

PORTS screen display. 

All of this information will be used to improve and modify the model system design before it 

becomes operational.

 
Figure 2.1. New York Harbor PORTS stations maintained by NOS.
Figure 2.2. Water level at Bayonne Bridge; (a) observations and astronomical tide prediction, 

(b) surface wind observations, and (c) observations and astronomical tide prediction 

over-laid with model water level nowcast and forecasts.
Figure 2.3. Parameters and locations that marine pilots request for navigation. 

3. SYSTEM OVERVIEW

The NYEFS provides near real-time water level and current nowcasts and forecasts using a 

hydrodynamic model forced with water levels at the open ocean boundary and with winds on the 

water surface. The hydrodynamic model used for the system, as described in detail in Wei and 

Chen (2001), is a three-dimensional barotropic model based on the Princeton Ocean Model 

(POM, Blumberg and Mellor, 1987). The model requires forcing of real-time water levels and 

winds acquired from NOS=s PORTS, water level forecasts acquired from the Extra-Tropical 

Storm Surge (ETSS) model (Chen et al., 1993; Kim et al., 1996), and wind forecasts acquired 

from the Eta (Black, 1994) model. The model grid information including bathymetry data is 

stored as a separate file. Data acquired are then formated to be read directly by the model. With 

the near real-time input data and the initial conditions created by the previous nowcast, the 

hourly nowcast is executed to obtain the water levels and currents throughout the entire model 

grid for the past hour. The nowcast model fields at 05Z and 17Z are used for the 36 hour 

forecast run forced with Eta wind and ETSS water level forecasts. Monthly climatological river 

discharges for the Raritan, Passic, Hakensack, and Hudson Rivers (Figure 1.1), generated from 

USGS (U.S. Geological Survey) observations are used as fresh water input to the model. The 

output from the nowcast and forecast runs are processed and plotted with graphic application for 

posting on the Internet. The NYEFS is implemented by various Unix scripts. Each script 

performs different operations including data gathering and quality control, executing nowcast 

and forecast simulations, and output data processes for product dissemination and graphic 

preparation. A schematic of the NYEFS system is shown in Figure 3.1 and also described in the 

following sections. 

3.1. Data Ingest and Boundary Forcing Generation

The data required for driving the model nowcast and forecast include the water levels as lateral 

open boundary conditions and winds as the surface forcing. For nowcast runs, near real-time 

water levels and winds at National Water Level Observation Network (NWLON) stations 

(Figure 2.1); Sandy Hook, NJ and Kings Point, NY (switching from Willets Points, NY on 

November 14, 2000) and are available in PORTS Uniform Flat File Format (PUFFF) format for 

anonymous ftp (File Transfer Protocol) through Internet from the NYPORTS data base server in 

CO-OPS. The near real-time water levels are acquired every 6 minutes and are processed hourly 

before the nowcast run. The non-tidal water levels are obtained by subtracting the astronomical 

tide prediction from the observations. In the case of data interruption, such as connection failure 

or erroneous data values, the non-tidal water levels are persisted and added to the tide predictions 

as a substitute for open boundary conditions at Sandy Hook and Willets Point. Therefore, the 

hourly nowcast run can be continued without interruption. Except when a strong wind prevails 

for a long duration, the water levels within the harbor are predominately determined by the water 

levels at the lateral open boundary, Sandy Hook. Therefore, in the case of data interruption, the 

nowcast can safely run without any wind forcing.
Figure 3.1. Schematic of the NYEFS system operation function element. 
Winds at Bayonne Bridge are also obtained for model input. Water levels at Bayonne Bridge 

and The Battery, and current velocity at The Narrows (starting July, 2001) are also acquired for 

model verification purpose. 

For the forecast, the wind-driven water level forecasts produced by NWS=s Meteorological 

Development Laboratory (MDL) ETSS are acquired by NOS=s Operational Data Acquisition and 

Archive System (ODAAS, Kelley et. al.,2001) as the lateral open boundary condition. Since 

ETSS water level forecasts have a consistent datum bias, a correction procedure has been applied 

to reduce the errors. The correction procedure includes two steps. First, the averaged 

discrepancy between the previous 24 hour forecasts and observations at the NYEFS model open 

boundaries: Sandy Hook, NJ and Kings Pt., NY, are calculated. The entire present 24 hour 

forecasts are then corrected by the averaged datum discrepancy. Even after the datum bias 

correction, there is a water level gap between the last observed and the first forecast water level. 

To prevent any model instability from occurring, the first 6 hour datum-corrected forecasts are 

smoothed. The smoothed water level forecasts are then added to the tide predictions at Sandy 

Hook, NJ and Kings Point, NY for the model lateral open boundary conditions. Wind velocity 

forecasts acquired by ODAAS from the Eta model are used for surface forcing. Water level and 

wind data ingested for nowcast and forecast model runs are also archived for further evaluation. 

3.2. Nowcast Run

The water level and wind boundary forcing fields at Sandy Hook and Willets Point are used to 

drive the hourly nowcast run. The model is initialized with the fully developed state from the 

previous nowcast run. The beginning hour is determined by the restart initial file. This hourly 

nowcast run produces the water levels and three-dimensional currents for the entire model grid. 

A restart file describing the entire mode grid ocean condition is also created for the next hourly 

nowcast run, or for the forecast run. Water level and current at selected locations are processed 

for plotting the time series. Water surface elevation and currents throughout the model domain 

are also processed for the contour and current vectors plots, and displayed on the Internet web 

site. Nowcast data such as water levels at model interior NWLON locations Bayonne Bridge and 

The Battery, and currents at Bergen Point, Bayonne Bridge, and The Narrows (Figure 2.1), are 

also archived for model skill assessment. Water levels at additional locations (Figure 3.2), where 

no operational observations available, are also output for time series plotting.

3.3. Forecast Run

The twice a day forecast runs start when the forecast forcing input files, as described in Section 

3.1, are generated. The monthly climatological river discharges that are used in the nowcast are 

also used for the forecast. The model forecast is initialized with the fully developed state of 

motion field of the model nowcast. The model runs for the 36 hour forecast and the output 

similar to the nowcast, i.e., water level and current throughout the entire domain and at selected 

locations, are processed and plotted. Model forecasts are also archived for the skill assessment.
Figure 3.2. Station locations available for model system water level output.
3.4. Operational Environment and Scheduling

The NYEFS is running on two SGI (Silicon Graphic, Inc.) work stations at CSDL. The data 

ingest, model nowcast and forecast, and output post-processing are running on an SGI Origin 

2000 computer. This server is a high-end MIPS computer equipped with eight 400 MHz 

(megahertz) IP27 processors and 2 GB (gigabyte) total memory and is using the IRIX 6.5 

operating system. The IDL graphic software (Version 5.3) is used for generating water level and 

current time series, contour, and vector plots in gif or post-script format. The graphic server is 

an SGI Indigo2 computer equipped with a 195 MHz processor and 128 MB (megabyte) of 

memory. This server is also using the IRIX 6.5 operating system. 

The NYEFS nowcast schedule is shown in Figure 3.3. NYEFS performs the data ingest every 6 

minutes to acquire PUFFF data and process the hourly data at minute 7 each hour. The hourly 

model nowcast run is submitted at minute 8 each hour (or till input data process is completed). 

The nowcast output process is followed immediately after the nowcast completion. The 05Z and 

17Z forecast runs are submitted at 0520Z and 1720Z, respectively, for a 36-hour simulation. 

Shown in Figure 3.4, the forecast run starts with an initial condition defined by the 

corresponding hourly nowcast model field. Under a machine dedicated situation (i.e., no CPU 

competition), the hourly nowcast requires about 67 seconds in CPU time and the 36-hour 

forecast requires about 33 minutes.

3.5. System Interruption and Recovery Procedure

The NYEFS is implemented with UNIX scripts to control operation procedures. The run 

schedule of these scripts is controlled by an UNIX crontab. These scripts have been frequently 

modified and updated since the system commenced in 1999. For example, a procedure has been 

adopted to accommodate the real-time water level interruption at Sandy Hook and Willets Point. 

The procedure uses the Apersistent sub-tidal water level@ added to the astronomical prediction to 

obtain the model open boundary forcing so that the nowcast run can continue without 

interruption. However, unexpected interruption still occurs. The interruptions result from many 

reasons such as server shutdowns, network breakdowns, and NWLON station switches (from 

Willets Point to Kings Point). The forecast run can proceed without Eta wind forecasts, but it 

can not run without ETSS forecasts. A system interruption would occur if ETSS is not available 

from ODAAS. 

A manual recovery procedure has been developed for the nowcast run. The procedure is also 

implemented with a UNIX shell script. This script is submitted manually by entering date 

information including the year, month, day, and hour when the last valid coarse grid and fine 

grid model restart files exist. The recovery script generates water level and wind forcing from 

PORTS archives based on the date information entered. The model will then run in a hindcast 

mode to bring the nowcast up to the Anow@ time. After the recovery hindcast is completed the 

system will operate normally.
Figure 3.3. NYEFS nowcast run schedule.
Figure 3.4. NYEFS forecast run schematic flow chart.

4. SEMI-OPERATIONAL NOWCAST/FORECAST SKILL ASSESSMENT

Skill assessments for tidal simulations and test nowcast assessments have been reported as part 

of the NYEFS model documentation in Wei and Chen (2001). This report describes the model 

system performance based on NOS requirements of an operational nowcast/forecast system 

(NOS, 1999). According to NOS (1999), the definition of model run scenarios for semioperational nowcast/forecast are as follows: 

Semi-operational Nowcast: In this scenario, the model is forced with actual observational input 

data streams including open ocean boundary water levels, wind stresses, river flows, and possible 

water density variations. Significant portions of the data may be missing, so the model must be 

able to handle this. 

Semi-operational Forecast: In this scenario, the model is forced with actual other model forecasts 

including open ocean boundary water levels, wind, river flows, and water density variations. 

Initial conditions are generated by observed data. Significant portions of the data may be 

missing, so the model must be able to handle this. 

The NYEFS, as described in Chapter 3, has been implemented on CSDL=s SGI computers to 

produce hourly water level and current nowcasts and twice daily forecasts in New York Harbor. 

The water level model nowcasts and forecasts at NWLON station; Bayonne Bridge and The 

Battery are archived for system skill evaluation. Analysis (Wei and Chen, 2001) shows water 

level discrepancy from the fine grid and coarse are negligible but not current velocity. Therefore, 

if available, outputs from the fine grid model are used in the analysis described in this Chapter. 

4.1. Analysis Method

A standard suit of assessment statistics is defined in NOS (1999). Parameters in the suite are 

calculated based on the time series of observed and model simulated water levels at the Bayonne 

Bridge and The Battery. Defining the error as the observations minus the semi-operational 

nowcasts, these parameters are (NOS, 1999): 

(1) SM: Series mean. 

(2) SD: Standard deviation of the error. 

(3) RMSE: Root mean squared error. 

(4) CF(x): Central Frequency. Percentage of errors that lie within the limit "x 

(5) POF(x): Positive Outlier Frequency. Percentage of errors that are greater than x. 

(6) NOF(x): Negative Outlier Frequency. Percentage of errors that are less than x. 

(7) MDPO(x): Maximum Duration of Positive Outliers. A positive outlier event is two or more 

consecutive occurrences of an error greater than x. MDPO is the length (number of consecutive 

occurrences) of the longest event. 
(8) MDNO(x): Maximum Duration of Negative Outliers. A negative outlier event is two or more 

consecutive occurrences of an error less than -x. MDNO is the length (number of consecutive 

occurrences) of the longest event. 

(9) WOF(X): Worst Cas Outlier Frequency. Fraction (percentage) of errors that, given an error of 

magnitude exceeding X, that (1) the simulated value of water level is greater than the 

astronomical tide and the observed value is less thatn the astronomical tide or (2) the simulated 

value of water level is less than the astronomical tide and the observed value is greater than the 

astronomical tide. 

4.2. Skill Assessment for Water Level Nowcasts

Hourly water level model nowcasts at the Bayonne Bridge and The Battery NWLON stations 

have been archived daily for model system evaluations since April 1, 1999. Only data associated 

with normal model system operation are selected. The skill assessment described in this chapter 

is based on the time series archived between April 1, 1999 and July 31, 2001. Model data from 

April to September, 2000 were not saved and not included in the analysis. No observed water 

level data is available at the Bayonne Bridge station for March, 2000 and at The Battery from 

January to May, 2001. Simulated water levels at the Bayonne Bridge and The Battery are taken 

from the fine grid and coarse grid, respectively. There are 11,996 and 9,884 hourly water level 

data extracted from 6-minute interval model output, at the Bayonne Bridge and The Battery, 

respectively, included in the analysis. Figures 4.1 and 4.2 show a portion of the observed and 

model nowcast water level time series at the Bayonne Bridge and The battery. 

285 286 287 288 289 290

Julian Day (2000)

−1.5

−1

−0.5

0

0.5

1

1.5

Water Elevation (M, MSL)

Observations

Model Nowcasts Bayonne Bridge

Figure 4.1. Observed and model nowcast water level time series at the Bayonne Bridge, 

October 12 - 17, 2000. 
285 286 287 288 289 290

Julian Day (2000)

−1.5

−1

−0.5

0

0.5

1

1.5

Water Elevation (M, MSL)

Observations

Model Nowcasts The Battery

Figure 4.2. Observed and model nowcast water level time series at The Battery, October 12 - 

17, 2000. 

Water level semi-operational nowcast statistics at the Bayonne Bridge and The Battery are listed 

in Table 4.1. The criteria accepted by NOS are also included in the table. All model statistical 

parameters pass the criteria. The water level time series means (SM) between model simulated 

and observed data at both locations are very close indicating the model reference datum is 

correct. Time series difference root-mean-square errors (RMSE) are 7.3 cm at the Bayonne 

Bridge and 9.5 cm at The Battery. 

A standard suite of assessment statistics for amplitude and time of high and low water are 

computed for the Bayonne Bridge and The Battery. Simulated water levels at the Bayonne 

Bridge and The Battery are taken from the fine grid and coarse grid, respectively. The high and 

low water time series subsets are derived from the entire 6-minute interval simulated and 

observed water level time series and the differences are computed. 

The standard suite of statistical parameters are derived and listed in Tables 4.2 and 4.3. All 

statistical parameters at the Bayonne Bridge are within NOS accepted criteria. The simulated 

high and low water lags behind the observations about 20 minutes at both locations. At both 

locations, the mean model high water amplitudes are higher than the observations and the mean 

model low water amplitudes are lower than the observations. 
Table 4.1. Model system water level nowcast skill assessment standard statistics for complete 

time series at Bayonne Bridge and The Battery. (Note: na = not applicable)

Bayonne Bridge The Battery 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria 

SM (cm) 5.9 6.5 0.6 6.5 7.1 0.5 na 

SD (cm) na na 7.3 na na 9.5 na 

RMSE (cm) na na 7.3 na na 9.5 na 

CF (15 cm) % 97.4 92.4 $90 

POF (30 cm) % 0.2 0.2 # 1 

NOF (30 cm) % 0.1 0.1 # 1 

MDPO (30 cm) (Hour) 5 4 # 24 

MDNO (30 cm) (Hour) 2 2 # 24 

WOF (30 cm) % 0.1 0.1 #0.5 

Table 4.2. High and low water level nowcast skill assessment standard suite statistics at the 

Bayonne Bridge. (Note: na = not applicable) 

Bayonne Bridge 

High Water Low Water 

Amplitude Time Amplitude Time 

NOS Accepted 

Criteria 

Difference SM (cm) (min) 4.6 15.1 -1.6 0.5 na 

Difference SD (cm) (min) 6.7 15.4 4.6 12.6 na 

RMSE (cm) (min) 8.1 21.6 4.9 12.6 na 

CF (15 cm) (30 min) % 96.1 90.1 99.1 97.8 $ 90 

POF (30 cm) (60 min) % 0.3 0.7 0.3 0.2 #1 

NOF (30 cm) (60 min) % 0 0.3 0 0.4 #1 

MDPO (30 cm) (#) 2 1 2 1 # 3 

MDNO (30 cm) (#) 0 1 0 1 # 3 
Table 4.3. High and low water level nowcast skill assessment standard suite statistics at The 

Battery. (Note: na = not applicable) 

The Battery 

High Water Low Water 

Amplitude Time Amplitude Time 

NOS Accepted 

Criteria 

Difference SM (cm) (min) 8.9 14.8 -7.2 7.1 na 

Difference SD (cm) (min) 4.1 12.3 4.3 11.5 na 

RMSE (cm) (min) 9.8 19.2 8.4 13.5 na 

CF (15 cm) (30 min) % 96.1 92.6 98.4 97.9 $ 90 

POF (30 cm) (60 min) % 0.3 0.4 0.3 0.3 #1 

NOF (30 cm) (60 min) % 0 0 0.1 0.1 #1 

MDPO (30 cm) (#) 2 1 2 1 # 24 

MDNO (30 cm) (#) 0 0 1 1 # 24 

4.3. Skill Assessment for Water Level Forecasts

The NYEFS makes an 36-hour forecast run twice a day. Each forecast run uses the datumcorrected ETSS subtidal water level forecasts, added to the astronomical tide predictions at 

Sandy Hook, NJ and Willets Pt. (Kings Point), NY as lateral open ocean boundary conditions. 

The other lateral open boundary condition is the climatological river flow described at river 

mouths. The model is forced with Eta forecasts on the surface. The forecast runs start the 

simulation at 05Z and 17Z and produce water level and three-dimension current forecasts over 

36 hours. Hourly water level data of the first 24 hours of the forecasts, at the Bayonne Bridge 

and The Battery, from October, 2000 to July 2001, are used for the skill assessment. There are 

about 270 days (two forecast cycles each day) of valid model data. However, observed data at 

The Battery are not available between January1, and April 30, 2001. Figures 4.3 and 4.4 show 

the observed and model forecast water level time series at the Bayonne Bridge and The Battery. 

According to NOS (1999), the statistic parameters including CF, POF, NOF, MDPO, MDNO 

and RMSE, at each forecast hour are calculated. The statistics from the 05z and 17z cycles are 

similar although the 05z cycle statistics are slightly better than 17z cycle in general. Tables 4.4 

and 4.5 list these parameters at each forecast hour (hour 1, 6, 12, 18, and 24 are highlighted) 

using the two cycle model forecast data.The overall statistics are listed as Table 4.6.
285 286 287 288 289 290

Julian Day (2000)

−1.5

−1

−0.5

0

0.5

1

1.5

Water Elevation (M, MSL)

Observations

Model Forecasts Bayonne Bridge

Figure 4.3. Observed and model forecast water level time series at the Bayonne Bridge, 

October 12 - 17, 2000. 

285 286 287 288 289 290

Julian Day (2000)

−1.5

−1

−0.5

0

0.5

1

1.5

Water Elevation (M, MSL)

Observations

Model Forecasts The Battery

Figure 4.4. Observed and model forecast water level time series at The Battery, October 12 - 17, 

2000. 
Table 4.4. Model system water level forecast skill assessment standard statistics for complete 

time series (two cycle forecasts) at Bayonne Bridge. (Note: Overall RMSE average: 13.4 cm.) 

Forecast CF POF NOF RMSE 

 Hour (15 cm) (30 cm) (30 cm) (cm) 

 1 97.2 0.4 0.0 6.9 

 2 86.2 0.9 0.2 10.6 

 3 86.8 0.6 0.4 10.7 

 4 84.6 0.2 0.6 10.9 

 5 83.8 1.1 0.4 11.8 

 6 79.0 1.5 0.6 12.2 

 7 82.5 0.9 0.9 12.0 

 8 66.2 5.8 3.0 16.9 

 9 70.1 5.0 1.1 14.9 

 10 79.9 1.9 0.2 12.1 

 11 75.8 1.9 0.7 13.1 

 12 79.4 2.4 0.2 12.6 

 13 74.7 1.5 0.4 12.7 

 14 73.4 2.0 1.7 13.7 

 15 74.3 2.0 2.4 14.0 

 16 68.8 1.7 2.2 14.7 

 17 69.1 2.8 2.2 15.2 

 18 70.3 3.2 2.2 15.0 

 19 70.6 3.0 1.9 15.1 

 20 68.8 3.5 2.6 15.4 

 21 69.5 3.2 2.4 15.1 

 22 72.1 2.4 1.5 14.4 

 23 74.2 2.0 1.7 13.7 

 24 75.1 2.4 1.7 13.6 

__________________________________________________________________ 

Table 4.5. Model system water level forecast skill assessment standard statistics for complete 

time series (two cycle forecasts) at The Battery. (Note: Overall RMSE average: 14.3 cm.) 

Forecast CF POF NOF RMSE 

 Hour (15 cm) (30 cm) (30 cm) (cm) 

 1 89.9 0.0 3.6 11.2 

 2 82.1 0.0 3.3 12.7 

 3 77.2 0.3 3.6 13.5 

 4 75.2 0.0 2.6 13.5 

 5 74.9 0.7 2.0 13.8 

 6 74.6 0.3 2.6 13.8 

 7 73.0 1.0 1.3 12.9 

 8 67.8 2.9 1.6 15.6 

 9 72.6 2.3 1.3 14.0 

 10 77.9 1.0 2.9 13.2 

 11 75.2 1.0 2.9 13.9 

 12 73.6 0.7 3.6 14.1 

 13 72.0 0.0 2.9 14.3 

 14 73.0 1.0 3.6 14.9 

 15 68.1 0.7 5.2 15.1 

 16 66.4 0.7 4.6 15.1 

 17 65.1 1.3 3.9 15.4 

 18 66.8 1.3 3.6 15.5 

 19 66.8 2.9 2.3 15.4 

 20 67.1 3.3 1.6 15.2 

 21 72.3 3.6 1.3 14.7 

 22 72.6 2.9 1.6 14.6 

 23 71.7 1.6 2.9 14.4 

 24 70.7 0.7 2.9 14.4 

_________________________________________________________ 
Table 4.6. Model system water level forecast skill assessment standard statistics for complete 

time series at Bayonne Bridge and The Battery. (Note: na = not applicable)

Bayonne Bridge The Battery 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria 

SM (cm) 5.1 6.7 1.6 6.5 7.5 -1.5 na 

SD (cm) na na 13.3 na na 14.2 na 

RMSE (cm) na na 13.4 na na 14.3 na 

CF (15 cm) % 76.4 72.8 $90 

POF (30 cm) % 2.2 1.3 # 1 

NOF (30 cm) % 1.3 2.8 # 1 

MDPO (30 cm) (Hour) 10 6 # 24 

MDNO (30 cm) (Hour) 8 7 # 24 

WOF (30 cm) % 2.0 2.2 # 0.5 

Since the water level forecasts at Bayonne Bridge and The Battery heavily depend on the ETSS 

forecasts at Sandy Hook, NJ (the 00Z ETSS cycle described in Section 3.1), the accuracy of 

ETSS forecasts at Sandy Hook becomes important. Inter-comparison of ETSS forecasts with 

observations at Sandy Hook shows ETSS forecasts has consistent underestimated the sub-tidal 

water levels shown in Tables 4.7. Table 4.7 shows the RMSE of ETSS forecasts is 21.6 cm. The 

central frequency (15 cm) ranges from 30% to 50% and the NOF (30 cm) are greater than 10% 

and no POF. Several correction approaches have been tested, for example, corrected with the 

average of the discrepancy between the observations and forecasts of the previous one, five, 

seven, and ten days. Table 4.8 shows the statistics of ETSS forecasts after the correction 

procedure using the previous one-day average discrepancy approach. The RMSE has been 

reduced to 13.3 cm and the CF increased to greater than 90% out to forecast hour 6. The 

corrected RMSE using other methods are all greater than 13 cm. The water level boundary 

conditions for semi-operational forecast runs are based on the previous one-day descrepancy 

correction. 

The water level forecast errors at the Bayonne Bridge and The Battery are expected to be greater 

than that at Sandy Hook. Shown in Tables 4.5 and 4.6 the Central Frequency CF decreases to 

about 80% and 74% at forecast hour 6 at the Bayonne Bridge and The Battery, respectively. At 

the Bayonne Bridge, the POF is greater than 1% after forecast hour 4 while the NOF is less than 

1% up to forecast hour 13, except at forecast hours 8 and 9. At The Battery, the NOF is much 

greater than the POF for all forecast hours and the RMSE (14.3 cm) is greater than at the 

Bayonne Bridge. 
Table 4.7. ETSS water level forecast skill assessment standard statistics at Sandy Hook. (Note: 

Overall RMSE average: 21.6 cm.) 

 Forecast CF POF NOF RMSE 

 Hour (15 cm) (30 cm) (30 cm) (cm) 

 1 30.0 0.0 16.6 25.0 

 2 27.9 0.0 19.1 25.5 

 3 31.4 0.0 15.5 24.9 

 4 42.8 0.4 12.4 22.1 

 5 49.8 0.0 10.2 20.2 

 6 51.2 0.0 8.1 18.9 

 7 49.5 0.0 9.5 19.8 

 8 46.3 0.0 9.9 20.2 

 9 39.9 0.0 13.1 21.4 

 10 38.5 0.0 13.8 21.7 

 11 42.8 0.0 11.3 20.8 

 12 49.8 0.0 9.2 20.4 

 13 55.5 0.0 9.2 21.3 

 14 53.4 0.0 11.0 21.5 

 15 54.1 0.0 11.7 21.7 

 16 51.9 0.0 10.6 22.1 

 17 53.0 0.0 13.4 21.8 

 18 51.9 0.0 13.8 21.4 

 19 49.1 0.0 14.5 21.2 

 20 48.8 0.0 12.7 21.6 

 21 50.2 0.0 14.5 20.9 

 22 49.8 0.0 15.2 20.3 

 23 50.9 0.0 15.2 20.8 

 24 44.9 0.0 18.7 23.5 

_______________________________________________________ 

Table 4.8. ETSS water level forecast skill assessment standard statistics at Sandy Hook after 

the correction. (Note: Overall RMSE average: 13.3 cm) 

Forecast CF POF NOF RMSE 

 Hour (15 cm) (30 cm) (30 cm) (cm) 

 1 93.3 0.0 1.4 9.9 

 2 90.1 0.4 0.7 11.0 

 3 90.8 0.4 1.8 12.1 

 4 92.9 0.7 1.4 10.5 

 5 91.9 1.1 0.7 9.8 

 6 94.0 1.1 0.4 9.5 

 7 84.1 2.5 1.8 13.3 

 8 82.0 1.8 1.8 13.0 

 9 79.5 1.4 0.7 12.5 

 10 79.9 1.1 0.7 12.4 

 11 79.5 0.7 0.7 12.2 

 12 80.6 1.1 1.1 13.4 

 13 76.7 2.1 2.5 15.6 

 14 76.7 2.1 2.1 15.2 

 15 78.1 2.8 1.8 15.2 

 16 74.6 1.8 1.8 15.7 

 17 76.3 2.1 2.5 15.0 

 18 77.4 1.4 2.8 14.5 

 19 74.2 1.4 1.4 14.0 

 20 75.3 2.1 1.4 14.1 

 21 75.6 2.1 1.4 14.0 

 22 73.9 1.8 1.8 13.6 

 23 76.3 1.8 1.8 13.9 

 24 75.6 1.1 3.2 14.7 

________________________________________________________ 
The NYEFS water level forecasts are then compared with astronomical tide predictions at the 

Bayonne Bridge and The Battery. Table 4.9 lists the skill assessment parameters for overall time 

series between forecasts/predictions and observations from October, 2000 to July, 2001. 

At the Bayonne Bridge, the model water level forecast skills do not meet the NOS accepted 

criteria, however, they are still better than the astronomical tide prediction skills when the 

MDPO and MDNO are greater than 24 hours. At The Battery, the NYEFS forecasts only show 

slight accuracy improvement over astronomical tide predictions. The astronomical tide 

predictions at The Battery has 48 hours MDNO and negative difference series mean (SM) 

indicating strong subtidal signal during this period. 

Table 4.9. NYEFS water level forecast and astronomical tide prediction skill assessment 

standard suite statistics at the Bayonne Bridge and The Battery. (Note: na = not applicable) 

Bayonne Bridge The Battery 

NYEFS Tide 

Predictions 

NYEFS Tide 

Predictions 

NOS 

Accepted 

Criteria 

Difference SM (cm) 1.8 -6.0 -1.5 -7.9 na 

Difference SD (cm) 13.3 17.3 14.2 14.4 na 

RMSE (cm) 13.4 18.3 14.3 16.4 na 

CF (15 cm) % 76.4 65.6 72.8 71.0 $ 90 

POF (30 cm) % 2.2 3.1 1.3 1.2 #1 

NOF (30 cm) % 1.3 5.7 2.8 5.8 #1 

MDPO (30 cm) (#) 10 26 6 7 # 3 

MDNO (30 cm) (#) 8 47 7 48 # 3 

A standard suite of assessment statistics for forecast water level amplitude and times of high and 

low water are computed for the Bayonne Bridge and The Battery. Simulated water levels at the 

Bayonne Bridge and The Battery are taken from the fine grid and coarse grid, respectively. The 

high and low water time series subsets are derived from the entire 6-minute interval simulated 

and observed water level time series and the differences are computed. The standard suite of 

statistical parameters are derived and listed in Tables 4.10 and 4.11. 

Similar to the entire forecast time series skill statistics, most of the forecast high and low water 

skill statistics for the Bayonne Bridge and The Battery do not meet the NOS criteria (NOS, 1999). 

The amplitude statistics CF at both locations are low compared with the time occurrence 

statistics CF. 
Table 4.10. High and low water level forecast skill assessment standard suite statistics at 

Bayonne Bridge. (Note: na = not applicable) 

Bayonne Bridge 

High Water Low Water 

Amplitude Time Amplitude Time 

NOS Accepted 

Criteria 

Difference SM (cm) (min) 10.4 7.3 -0.4 -5.8 na 

Difference SD (cm) (min) 11.0 21.6 10.8 20.9 na 

RMSE (cm) (min) 15.1 22.8 10.8 21.7 na 

CF (15 cm) (30 min) % 70.2 85.3 85.8 88.4 $ 90 

POF (30 cm) (60 min) % 5.0 1.6 0.6 1.2 #1 

NOF (30 cm) (60 min) % 0 0 0.8 1.2 #1 

MDPO (30 cm) (#) 2 1 1 1 # 24 

MDNO (30 cm) (#) 0 0 1 1 # 24 

Table 4.11. High and low water level forecast skill assessment standard suite statistics at The 

Battery. (Note: na = not applicable) 

The Battery 

High Water Low Water 

Amplitude Time Amplitude Time 

NOS Accepted 

Criteria 

Difference SM (cm) (min) 6.6 9.9 -8.7 -0.3 na 

Difference SD (cm) (min) 10.8 21.2 11.8 20.6 na 

RMSE (cm) (min) 12.7 23.4 14.6 20.6 na 

CF (15 cm) (30 min) % 77.5 87.8 73.4 92.1 $ 90 

POF (30 cm) (60 min) % 2.3 2 0 0.7 #1 

NOF (30 cm) (60 min) % 0 0.3 5.3 0.7 #1 

MDPO (30 cm) (#) 2 1 0 1 # 24 

MDNO (30 cm) (#) 0 1 3 1 # 24 
4.4. Skill Assessment for Persisted Water Level Forecasts 

A forecast method which provides timely information without running a hydrodynamic modeling 

is the so called persisted water level forecasts. In this method, the last available observed water 

level offset from the astronomical tide at a location is added to the future astronomical tide 

predictions to obtain the water level forecasts. This section describes the persisted water level 

forecasts skill assessments at The Battery and the Bayonne Bridge during the same period 

(October 1, 2000 – July 31, 2001) of the model forecast skill assessments described in Section 

4.3. 

The observed water level offset from the astronomical tide predictions at The Battery and the 

Bayonne Bridge at 05Z and 17Z were used to added to the followed 24 hours astronomical tide 

predictions as tpersisted water level forecasts. The persisted water level forecasts are then 

compared with observations to obtain the skill assessments as listed in Table 4.12. Comparing 

the skill assessments for the presisted water level forecasts (Table 4.12), the model water level 

forecast (Table 4.6), and the astronomical tide predictions (Table 4.9) shows that the CF, POF, 

and NOF for the persisted water level forecasts, especially at The Battery, are better than the 

other methods. However, the models’s MDPO and MDNO are lower than the other methods. 

Table 4.12. Persisted water level forecast skill assessment standard statistics at Bayonne Bridge 

and The Battery. (Note: na = not applicable)

Bayonne Bridge The Battery 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria 

SM (cm) 5.1 -1.1 -0.9 9.0 2.2 -0.6 na 

SD (cm) na na 14.7 na na 11.6 na 

RMSE (cm) na na 14.8 na na 11.6 na 

CF (15 cm) % 78.9 87.0 $90 

POF (30 cm) % 2.9 1.4 # 1 

NOF (30 cm) % 2.2 1.2 # 1 

MDPO (30 cm) (Hour) 23 17 # 24 

MDNO (30 cm) (Hour) 14 15 # 24 

WOF (30 cm) % 2.7 1.3 # 0.5 
4.5. Skill Assessment for Current Nowcasts

Nowcast Current Speed and Direction Skill Assessment at Bergen Point

Current observations about 4 m below the water surface (bin 8) are compared with simulated 

fine-grid model current speed and direction nowcasts at equivalent depth (fine-grid model layer 3) 

at Bergen Point from October 6 to December 3, 2000. The observations are low-passed with a 

90-minute filter to remove high frequency disturbances. Selection of both the observed and 

modeled co-existing data results in 12,000 total valid 6-minute interval data, equivalent to about 

51 days. The time difference (2 minutes) between simulated and observed data time has been 

neglected in calculating the statistics. The current speed time series between October 6 to 11, 

2000 are shown in Figure 4.5. The maximum flood current speeds are much stronger than the 

maximum ebb current speeds. The parameters in the analysis are obtained based on the entire 

data set except for MDPO and MDNO, which are based on each continuous data segment. 

280 281 282 283 284 285

Julian Day (2000)

0

30

60

90

120

Current Speed (cm/s)

Observations

Model Forecasts Bergen Point

Figure 4.5. Observed and model nowcast current speed time series (low-passed) at Bergen 

Point, October 6 - 11, 2000. 

Current speed and direction skill assessments for Bergen Point are listed in Table 4.13. The 

current speed CF (76.2%) is below the NOS acceptable criterion (90%). Current direction 

statistics (CF: 85.6%, POF: 0.7%, and NOF:0.6%) are better than the speed but CF is still below 

the accepted criterion. The speed RMS error of about 27 cm s-1 is mostly due to the phase lag of 

the simulated current speed. This can also be seen in the slack before flood (SBF) and slack 

before ebb (SBE) analysis results presented in Table 4.14. 
Table 4.13. Nowcast current speed and direction skill assessment standard suite statistics at 

Bergen Point, based on 12,384 six minutes interval data. (Note: na = not applicable) 

Speed Direction 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria

SM (cm/s) (deg) 28.3 44.7 16.3 228.7 232.3 3.5 na 

SD (cm/s) (deg) na na 21.9 na na 17.1 na 

RMSE (cm/s) (deg) na na 27.0 na na 17.5 na 

CF (26 cm/s) (22.5 deg)% 76.2 85.6 $ 90 

POF (52 cm/s)(45 deg) % 8.5 0.7 #1 

NOF (52 cm/s) (45 deg)% 0 0.6 #1 

MDPO (52 cm/s) (45 deg)(Hour) 2.3 0.9 # 24 

MDNO (52 cm/s)(45 deg) (Hour) 0 0.9 # 24 

Nowcast Current Slack Time at Bergen Point

The beginning and end time of SBE and SBF are defined as at the time when current speed is 

less/greater 0.26 cm s-1. The skill assessment for the beginning aand end time of SBE and SBF 

series at Bergen Point are computed. The observed and model simulated current nowcasts have 

3 gaps. Therefore, the beginning and end time of SBE and SBF are selected from each of 4 

continuous time series segments and then put together. Two sets of standard NOS statistics are 

then computed based on the differences of SBE and SBF beginning and end times between the 

observed and the model-based nowcast currents. Table 4.14 lists the statistical parameters for 

Bergen Point. The model performance does not meet NOS standards due to the complex flow 

pattern and horizontal current shears near Bergen Point. When the criteria were relaxed (time 

limit was doubled), the skills of CF, POF, and NOF are improved, although they are still below 

the NOS criteria (Table 4.14). 

Nowcast Maximum Flood and Ebb Currents at Bergen Point

Although these are not required by NOS (1999), the simulated time, speed, and direction of 

maximum flood and ebb currents at Bergen Point are also compared with the observations to 

evaluate the model system performance. Table 4.15 shows the skill statistics in terms of CF, 

RSME, POF, and NOF. 

It appears that RMSE for the speed and direction of maximum current is very low indicating the 

model performs well in defining the maximum current speeds and directions. However, the 

simulated time of maximum flood current lags behind the observations by 40 minutes (RMSE) 

(Figure 4.5). 
Table 4.14. Skill assessment standard suite statistics for begin and end times of SBE (slack 

before ebb) and SBF (slack before flood) differences between current observations (at bin 8) and 

nowcastss (at layer 3) at Bergen Point. (Note: na = not applicable) 

Bergen Point 

SBE SBF NOS Accepted Criteria 

SM (minutes) 29.0 37.5 na 

SD (minutes) 63.0 35.3 na 

RMSE (minutes) 69.0 51.5 na 

CF (15 minutes) % 10.9 25.3 $ 90 

POF (30 minutes) % 50.6 45.4 #1 

NOF (30 minutes) % 16.0 0.7 #1 

CF (30 minutes) % 33.3 53.9 

POF (60 minutes) % 37.2 22.7 

NOF (60 minutes) % 4.5 0 

Table 4.15. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 8) and nowcast currents (in layer 3) at 

Bergen Point. (Note: na = not applicable) 

Maximum Flood Current Maximum Ebb Current 

Tim

e 

Speed Direction Tim

e 

Speed Direction 

SM (min) (cm/s) (deg) 34.8 23.3 10.7 9.3 9.5 -2.0 

SD (min) (cm/s) (deg) 24.1 13.0 3.2 52.0 7.8 14.9 

RMSE (min) (cm/s) (deg) 42.3 26.7 11.1 52.5 12.2 15.0 

CF (30 min) (26 cm/s) (22.5 deg)% 44.4 64.7 99.0 47.5 99.0 85.9 

POF (60 min) (52 cm/s)(45 deg) % 16.2 2.0 0.0 20.2 0.0 0.0 

NOF (60 min) (52 cm/s) (45 deg)% 0.0 0.0 0.0 7.1 0.0 0.0
Nowcast Current Speed and Direction at The Narrows

In July, 2001, NOS installed a bottom mounted ADCP at The Narrows as part of the New York 

PORTS. Since August, 2001, the model system started archiving the nowcast and forecast 

currents from the coarse grid model at this location. Current observations about 6 m below water 

surface (bin 20) are compared with simulated current speed and direction nowcasts at the 

equivalent depth (model layer 2) from August 14 to November 19, 2001. Observations are lowpassed with a 90 minute period filter to remove high frequency disturbances. Selection of both 

the observed and modeled co-existing data results in almost 19,000 valid 6-minute samples, 

equivalent to about 79 days. The difference (2 to 3 minutes) between simulated and observed 

data time has been neglected in calaulating the statistics. The current speed time series from 

August 20 to 22, 2001 are shown in Figure 4.6. The maximum flood and ebb current difference 

is less than that at Bergen Point (Figure 4.5). The parameters in the analysis are obtained based 

on the entire data set except for MDPO and MDNO (maximum duration of positive/negative 

outliers), which are based on each continuous data segment. 

Current speed and direction skill assessments for The Narrows are listed in Table 4.16. The 

model simulated current speed and direction at The Narrows are more accurate than at Bergen 

Point because of simple geometry of the waterway. All parameters satisfy NOS criterion. 

231 232 233 234

Julian Day (2001)

0

30

60

90

120

150

Speed (cm/s)

Model Nowcasts

Observations The Narrows

Figure 4.6. Observed and model nowcast current speed time series (low-passed) at The 

Narrows, August 20 - 23, 2001.
Table 4.16. Current speed and direction nowcast skill assessment standard suite statistics at The 

Narrows, based on 18,985 six minutes interval data. (Note: na = not applicable) 

Speed Direction 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria

SM (cm/s) (deg) 58.1 57.9 -0.22 240.2 243.6 3.3 na 

SD (cm/s) (deg) na na 13.1 na na 11.5 na 

RMSE (cm/s) (deg) na na 13. na na 12.0 na 

CF (26 cm/s) (22.5 deg)% 94.7 95.2 $ 90 

POF (52 cm/s)(45 deg) % 0.0 0.8 #1 

NOF (52 cm/s) (45 deg)% 0.0 0.0 #1 

MDPO (52 cm/s) (45 deg)(Hour) 3 4 # 24 

MDNO (52 cm/s)(45 deg) (Hour) 0 1 # 24 

Nowcast Current Slack Time at The Narrows

The skill assessment for the beginning and end time of SBE and SBF series at The Narrows are 

computed. The observed and model simulated current nowcasts have 2 gaps. Therefore, the 

beginning and end time of SBE and SBF are selected from each of 3 continuous time series 

segment and then put together. Two sets of standard NOS statistics are then computed based on 

the differences of SBE and SBF beginning and end times between observed and model-based 

tidal currents. Table 4.17 lists the statistical parameters for The Narrows. Although the statistics 

are better than that at Bergen Point, the slack time performance is still below NOS acceptable 

criteria. When the criteria was relaxed (the time limit was doubled), the skills of CF, POF, and 

NOF are improved, although still below the criteria. 
Table 4.17. Skill assessment standard suite statistics for the beginning and end times of SBE 

(slack before ebb) and SBF (slack before flood) differences between current observations (at bin 

20) and forecasts (at layer 2) at The Narrows. (Note: na = not applicable) 

The Narrows 

SBE SBF NOS Accepted Criteria 

SM (minutes) -0.2 -27.8 na 

SD (minutes) 13.2 19.9 na 

RMSE (minutes) 13.1 34.2 na 

CF (15 minutes) % 78.2 25.5 $ 90 

POF (30 minutes) % 1.3 0.0 #1 

NOF (30 minutes) % 1.7 41.3 #1 

CF (30 minutes) % 97.0 58.7 

POF (60 minutes) % 0.0 0.0 

NOF (60 minutes) % 0.0 7.1 

Nowcast Maximum Flood and Ebb Currents at The Narrows

Although these are not required by NOS (1999), the model nowcast time, speed, and direction of 

maximum flood and ebb currents at The Narrows are also compared with observations to 

evaluate the model system performance. Table 4.18 shows the skill statistics in terms of CF, 

RSME, POF, and NOF. Note that the criteria variable for time has been set to 30 minutes. 

Table 4.18 shows that the CF for the speed and direction of maximum currents are 100% 

indicating that the model performs well in defining the maximum current speeds and directions. 

However, the simulated time of maximum flood current lags behind the observations by about 36 

minutes (RMSE) as shown in Figure 4.6. 
Table 4.18. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 20) and nowcasts (in layer 2) at The 

Narrows. (Note: na = not applicable) 

Maximum Flood Current Maximum Ebb Current 

Tim

e 

Speed Direction Tim

e 

Speed Direction 

SM (min) (cm/s) (deg) -17.0 2.7 7.6 -9.0 -12.6 -4.0 

SD (min) (cm/s) (deg) 31.9 6.7 6.5 35.3 6.8 8.9 

RMSE (min) (cm/s) (deg) 36.0 7.2 10.0 36.1 14.4 9.8 

CF (30 min) (26 cm/s) (22.5 deg)% 61.5 100.0 100.0 61.7 99.3 100.0 

POF (60 min) (52 cm/s)(45 deg) % 0.0 0.0 0.0 1.3 0.0 0.0 

NOF (60 min) (52 cm/s) (45 deg)% 0.0 0.0 0.0 7.4 0.0 0.0

4.5. Skill Assessment for Current Forecasts

Forecast Current Speed and Direction Skill Assessment at Bergen Point

ADCP current observations bout 4 m below the water surface (bin 8) are compared with 

simulated current speed and direction forecasts (05z cycle only) at the equivalent depth (fine-grid 

model layer 3) at Bergen Point from October 6 to December 3, 2000. The observations are lowpassed with a 90 minute filter to remove high frequency disturbances Selection of both the 

observed and modeled co-existing data results in over 11,000 valid 6-minute samples, equivalent 

to about 48 days. The time difference (2 minutes) between simulated and observed data time has 

been neglected in calculating the statistics. The current speed time series between October 6 to 

11, 2000 are shown in Figure 4.7. The model forecast current speed time series (Figure 4.7) are 

very similar to the nowcast (Figure 4.5). The parameters in the analysis are obtained based on 

the entire data set except for MDPO and MDNO (maximum duration of positive/negative 

outliers), which are based on each continuous data set. 

Current speed and direction skill assessments for Bergen Point are listed in Table 4.19. The 

statistics ire very similar to the nowcasts (Table 4.13). The current speed CF (75.9%) is below 

the NOS acceptable criterion (90%). Tables 4.20 and 4.21 lists the 24 hour current speed and 

direction forecast statistics. The speed CF ranges from 60% to 84% throughout the 24 forecast 

hours, but not necessary degrading with time. The POFs are greater than 1% for all Forecast 

hours, however, most of the NOFs are less than 1%. 
280 281 282 283 284 285

Julian Day (2000)

0

20

40

60

80

100

120

Current Speed (cm/s)

Model

Observations Bergen Point

Figure 4.7. Observed and model forecast current speed time series (low-passed) at Bergen Point, 

October 6 - 11, 2000.

Table 4.19. Forecast current speed and direction skill assessment standard suite statistics at 

Bergen Point, based on 11,674 six minute interval data. (Note: na = not applicable) 

Speed Direction 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria

SM (cm/s) (deg) 28.2 44.2 16.0 228.9 232.5 3.6 na 

SD (cm/s) (deg) na na 21.2 na na 16.4 na 

RMSE (cm/s) (deg) na na 26.6 na na 16.9 na 

CF (26 cm/s) (22.5 deg)% 75.9 85.4 $ 90 

POF (52 cm/s)(45 deg) % 8.0 0.3 #1 

NOF (52 cm/s) (45 deg)% 0.0 0.6 #1 

MDPO (52 cm/s) (45 deg)(Hour) 22 3 # 24 

MDNO (52 cm/s)(45 deg) (Hour) 3 8 # 24 
Table 4.20. Model system current speed forecast statistics at each of the 24 forecast hour at 

Bergen Point. (Note: Overall RMSE average: 29 cm.s-1) 

Forecast CF POF NOF RMSE 

 Hour (26 cm s-1) (52 cm s-1) (52 cm s-1) (cm s-1) 

 1 81.2 2.3 0.0 20.5 

 2 82.7 3.8 0.0 21.9 

 3 73.7 6.8 0.0 25.1 

 4 71.4 5.3 0.0 26.2 

 5 68.4 9.8 0.0 29.5 

 6 71.4 12.8 0.8 31.4 

 7 65.4 15.8 0.0 33.0 

 8 65.4 6.0 1.5 29.8 

 9 72.9 9.0 0.8 27.2 

 10 76.7 4.5 0.8 68.7 

 11 81.2 1.5 0.0 22.3 

 12 75.2 6.8 0.0 25.7 

 13 78.2 2.3 0.0 22.7 

 14 81.2 6.0 0.0 23.0 

 15 75.9 5.3 0.0 23.9 

 16 70.7 9.0 0.0 27.2 

 17 68.4 11.3 0.0 30.7 

 18 70.7 15.0 0.0 32.4 

 19 69.9 11.3 0.0 29.7 

 20 66.2 5.3 1.5 28.4 

 21 75.2 9.0 1.5 26.5 

 22 79.7 3.8 0.0 23.9 

 23 82.0 2.3 0.0 21.2 

 24 84.2 0.0 1.5 19.3 

________________________________________________________ 

Table 4.21. Model system current direction forecast statistics at each of 24 Forecast hour at 

Bergen Point. (Note: Overall RMSE average: 20.0 degrees)

Forecast CF POF NOF RMSE 

 Hour (22 deg) (45 deg) (45 deg) (deg) 

 1 78.6 2.9 0.0 19.5 

 2 84.3 0.0 0.0 17.9 

 3 87.0 1.4 0.0 16.9 

 4 79.2 1.4 1.4 19.9 

 5 79.4 1.5 1.5 18.7 

 6 76.3 3.4 3.4 20.5 

 7 83.6 1.8 0.0 17.6 

 8 80.4 1.8 1.8 29.5 

 9 75.4 1.8 0.0 19.6 

 10 76.8 4.3 0.0 20.0 

 11 87.7 0.0 1.5 18.4 

 12 77.4 0.0 0.0 18.3 

 13 82.1 0.0 0.0 16.0 

 14 84.0 1.3 0.0 17.3 

 15 84.5 0.0 1.4 16.0 

 16 83.3 1.5 1.5 18.6 

 17 76.9 1.5 3.1 20.1 

 18 83.6 0.0 0.0 16.2 

 19 77.2 0.0 0.0 18.9 

 20 74.1 3.7 1.9 43.2 

 21 81.1 0.0 0.0 18.2 

 22 88.9 1.6 0.0 15.7 

23 80.0 0.0 0.0 16.8 

 24 79.2 0.0 0.0 16.8 

_________________________________________________ 
Forecast Current Slack Time at Bergen Point

The skill assessment for the beginning and end time of SBE and SBF series at Bergen Point are 

computed. The observed and model simulated current forecasts have 3 gaps. Therefore, the 

beginning and end time of SBE and SBF are selected from each of 4 continuous time series 

segments and then put together. Two sets of standard NOS statistics are then computed based on 

the differences of SBE and SBF beginning and end times between the observed and the modelbased forecast currents. Table 4.22 lists the statistical parameters for Bergen Point. Similar to 

the nowcast, the forecast current slack time statistics do not meet NOS standards due to the 

complex flow pattern and horizontal current shears near Bergen Point. The skills of CF, POF, 

and NOF have been improved, although still below the criteria, when the criteria was relaxed. 

Table 4.22. Skill assessment standard suite statistics for begin and end times of SBE (slack 

before ebb) and SBF (slack before flood) differences between current observations (at bin 20) 

and forecasts (at layer 2) at Bergen Point. (Note: na = not applicable) 

The Narrows 

SBE SBF NOS Accepted Criteria 

SM (minutes) 28.7 33.5 na 

SD (minutes) 64.4 38.0 na 

RMSE (minutes) 70.4 50.6 na 

CF (15 minutes) % 8.7 24.0 $ 90 

POF (30 minutes) % 49.3 42.5 #1 

NOF (30 minutes) % 14.0 1.4 #1 

CF (30 minutes) % 36.7 56.2 

POF (60 minutes) % 37.3 21.2 

NOF (60 minutes) % 4.7 0.0 

Forecast Maximum Flood and Ebb Currents at Bergen Point

The model forecast time, speed, and direction of maximum flood and ebb currents at Bergen 

Point are also compared with the observations to evaluate the model system performance. Table 

4.23 shows the skill statistics in terms of CF, RSME, POF, and NOF. Note that the criteria 

variable for time has been set to 30 minutes. 
Table 4.23 shows that the CF for the speed and direction of maximum currents are near 100%, 

except maximum ebb direction (87.9%), indicating that the model performs well in defining the 

maximum current speeds and directions. However, the forecast time of maximum flood current 

lags behind the observations by greater than 30 minutes RMSE. 

Table 4.23. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (bin 20) and forecasts (fine-grid model layer 

2) at Bergen Point. (Note: na = not applicable) 

Maximum Flood Current Maximum Ebb Current 

Time Speed Direction Time Speed Direction 

SM (min) (cm/s) (deg) 44.2 23.6 10.2 10.5 11.6 -1.9 

SD (min) (cm/s) (deg) 27.4 13.4 2.4 79.2 7.1 14.5 

RMSE (min) (cm/s) (deg) 52.0 27.1 10.4 79.2 13.5 14.5 

CF (30 min) (26 cm/s) (22.5 deg)% 36.1 65.1 100.0 28.3 98.3 88.3 

POF (60 min) (52 cm/s)(45 deg) % 31.3 2.4 0.0 36.7 0.0 0.0 

NOF (60 min) (52 cm/s) (45 deg)% 0.0 0.0 0.0 18.3 0.0 0.0

Forecast Current Speed and Direction at The Narrows

The current forecasts from the experimental model system at The Narrows from August 20 to 

November 30, 2002 are compared with observations. Adjusting both forecasts and observations, 

based on data gaps, results in near 19,000 records of 6 minutes samples of forecasts in model 

layer 2 and observations in bin 20. The time difference for each corresponding forecast and 

observation record is about 2 to 3 minutes, which has been neglected in the analysis. Current 

speed and direction skill assessments for The Narrows are listed in Table 4.24. The statistics is 

very similar to the nowcasts (Table 4.16). All parameters satisfy NOS criterion except for the 

POF (2.2%) direction statistic. 
Table 4.24. Current speed and direction forecast skill assessment standard suite statistics at The 

Narrows, based on 18,935 six minute interval data. (Note: na = not applicable) 

Speed Direction 

Observed Model Difference Observed Model Difference 

NOS 

Accepted 

Criteria

SM (cm/s) (deg) 56.1 56.5 0.4 238.1 238.3 5.6 na 

SD (cm/s) (deg) na na 13.1 na na 24.1 na 

RMSE (cm/s) (deg) na na 13. na na 24.1 na 

CF (26 cm/s) (22.5 deg)% 95.1 92.0 $ 90 

POF (52 cm/s)(45 deg) % 0.0 2.2 #1 

NOF (52 cm/s) (45 deg)% 0.0 0.2 #1 

MDPO (52 cm/s) (45 deg)(Hour) 2 14 # 24 

MDNO (52 cm/s)(45 deg) (Hour) 0 6 # 24 

The statistics, including CF, POF, NOF, and RMSE, for the current speed forecasts at The 

Narrows at each of the 24 forecast hours are calculated and listed in Table 4.25. Most of the 

central frequency (CF) are either exceeding or close to the NOS (1999) criteria. The outliers 

(POF and NOF) also pass the NOS standards, except for POF at Forecast hour 20 (1.3%). This 

indicates that the model forecast current speed at The Narrows is very accurate. Table 4.26 lists 

the 24 hour forecast statistics for the direction. The RMSE of the direction is 24.1 degrees. The 

statistics either exceed or are close to the NOS (1999) criteria. 
Table 4.25. Model system current speed forecast statistics at each of 24 Forecast hour at The 

Narrows. (Note: Overall RMSE average: 13 cm.s-1) 

Forecast CF POF NOF RMSE 

 Hour (26 cm s-1) (52 cm s-1) (52 cm s-1) (cm s-1) 

 1 96.1 0.0 0.0 14.3 

 2 96.1 0.0 0.0 11.4 

 3 97.4 0.0 0.0 11.2 

 4 97.4 0.0 0.0 11.9 

 5 96.1 0.0 0.0 12.0 

 6 96.1 0.0 0.0 12.2 

 7 89.6 0.0 0.0 15.2 

 8 90.9 0.0 0.0 15.2 

 9 98.7 0.0 0.0 11.3 

 10 100.0 0.0 0.0 10.5 

 11 100.0 0.0 0.0 9.8 

 12 97.4 0.0 0.0 11.0 

 13 94.8 0.0 0.0 13.0 

 14 100.0 0.0 0.0 11.2 

 15 98.7 0.0 0.0 11.4 

 16 97.4 0.0 0.0 11.7 

 17 97.4 0.0 0.0 13.3 

 18 100.0 0.0 0.0 12.0 

 19 96.1 0.0 0.0 13.6 

 20 88.3 1.3 0.0 17.0 

 21 87.0 0.0 0.0 17.4 

 22 87.0 0.0 0.0 16.9 

 23 90.9 0.0 0.0 13.5 

 24 96.1 0.0 0.0 12.6 

_______________________________________________________ 

__________________________________________________________ 

Table 4.26. Model system current direction forecast statistics at each of 24 Forecast hour at The 

Narrows. (Note: Overall RMSE average: 24.1 degrees)

Forecast CF POF NOF RMSE 

 Hour (22 deg) (45 deg) (45 deg (deg) 

 1 90.0 3.3 0.0 38.3 

 2 93.1 1.7 0.0 14.2 

 3 88.7 1.6 0.0 17.9 

 4 95.1 0.0 0.0 11.3 

 5 95.1 0.0 0.0 10.8 

 6 100.0 0.0 0.0 9.0 

 7 95.0 1.7 0.0 12.4 

 8 90.2 0.0 0.0 12.4 

 9 88.9 1.6 0.0 25.8 

 10 93.7 0.0 0.0 11.7 

 11 89.2 3.1 0.0 26.0 

 12 92.1 1.6 0.0 23.8 

 13 92.2 0.0 0.0 13.2 

 14 89.2 3.1 0.0 16.5 

 15 87.5 3.1 0.0 17.8 

 16 95.1 0.0 0.0 12.3 

 17 90.6 4.7 0.0 16.6 

 18 95.3 1.6 0.0 12.7 

 19 96.8 0.0 0.0 11.8 

 20 91.7 3.3 0.0 33.6 

 21 89.2 4.6 0.0 39.4 

 22 88.5 4.9 0.0 63.7 

 23 88.5 1.6 0.0 27.9 

 24 93.0 1.8 1.8 16.6 

________________________________________________________ 
Forecast Current Slack Time at The Narrows

The skill assessment for the beginning and end time of SBE and SBF series at The Narrows are 

computed. The observed and model simulated current forecasts have 3 gaps. Therefore, the 

beginning and end time of SBE and SBF are selected from each of 4 continuous time series 

segment and then put together. Two sets of standard NOS statistics are then computed based on 

the differences of SBE and SBF beginning and end times between observed and model-based 

forecast currents. Table 4.26 lists the statistical parameters for The Narrows. The statistics are 

better than that at Bergen Point, however, they still do not meet NOS standard. The skills would 

be improved dramatically if the criteria was doubled (relaxed) (below the double line in Table 

4.27. 

Table 4.27. Skill assessment standard suite statistics for the beginning and end times of SBE 

(slack before ebb) and SBF (slack before flood) differences between current observations (at bin 

20) and forecasts (at layer 2) at The Narrows. (Note: na = not applicable) 

The Narrows 

SBE SBF NOS Accepted Criteria 

SM (minutes) 2.3 -24.2 na 

SD (minutes) 16.0 22.4 na 

RMSE (minutes) 16.1 33.0 na 

CF (15 minutes) % 66.6 33.5 $ 90 

POF (30 minutes) % 3.3 0.3 #1 

NOF (30 minutes) % 4.6 35.2 #1 

CF (30 minutes) % 92.1 64.4 

POF (60 minutes) % 0.0 0.0 

NOF (60 minutes) % 0.0 5.0 

Forecast Maximum Flood and Ebb Currents at The Narrows

The model forecast time, speed, and direction of maximum flood and ebb currents at The 

Narrows are also compared with observations to evaluate the model system performance. Table 

4.27 shows the skill statistics in terms of CF, RSME, POF, and NOF. Note that the criteria 

variable for time has been set to 30 minutes. 
Table 4.28 shows that the CF for the speed and direction of maximum currents are near 100%, 

except maximum ebb direction (87.9%), indicating that the model performs well in defining the 

maximum current speeds and directions. However, the forecast time of maximum flood current 

lags behind the observation by greater than 30 minutes (RMSE). 

Table 4.28. Skill assessment standard suite statistics for maximum current time, speed, and 

direction differences between current observations (at bin 20) and forecasts (in layer 2) at The 

Narrows. (Note: na = not applicable) 

Maximum Flood Current Maximum Ebb Current 

Time Speed Direction Time Speed Direction 

SM (min) (cm/s) (deg) -19.6 9.9 0.3 -11.8 -6.3 -11.1 

SD (min) (cm/s) (deg) 34.3 6.6 8.4 30.8 8.2 9.1 

RMSE (min) (cm/s) (deg) 39.4 11.9 8.4 32.9 10.3 14.4 

CF (30 min) (26 cm/s) (22.5 deg)% 47.6 99.3 99.3 61.1 98.7 87.9 

POF (60 min) (52 cm/s)(45 deg) % 0.0 0.0 0.7 0.7 0.0 0.0 

NOF (60 min) (52 cm/s) (45 deg)% 0.0 0.0 0.0 4.0 0.0 0.0
5. SUMMARY

An experimental nowcast/forecast water level and current model system for the Port of New 

York and New Jersey has been operational on CSDL computers since April 1999. The model 

system performs hourly nowcasts using observed water levels at Sandy Hook, NJ and Kings 

Point, NY as the lateral open boundary condition. The observed winds at Sandy Hook, NJ, 

Bayonne Bridge, NY, Robbins Reef, NY, and Kings Point, NY are used as model surface forcing. 

The nowcast model fields at 05Z and 17Z are used for 36 hours model forecast runs forced with 

Eta winds and ETSS water level forecasts. The modeled water levels at the Bayonne Bridge and 

The Battery, and the observed currents at Bergen Point, Bayonne Bridge, and The Narrows are 

used for the model system skill assessment. 

The skill assessment results indicate that most parameters either exceed, or are close to the NOS 

(1999) criteria. Due to the inaccuracy of subtidal water level forecasts from ETSS at Sandy 

Hook and Kings Point, the CF of the model simulated water levels at most of frecast hour are 

below NOS (1999) criteria. The current velocity nowcasts and forecasts at The Narrows, 

although from the coarse grid, are better modeled than at Bergen Point from the fine grid because 

of geometry complexity near Bergen Point. 

The model system uses the three-dimensional barotropic version of POM. Therefore the effects 

of density are not included. In the near future the barotropic model will be extended to include 

the salinity and temperature since commercial ship operations require the water density 

information for maximizing the cargo draft for avoiding grounding. The salinity and temperature 

information will not only be useful for navigational safety and efficiency but it will also be the 

key parametric input for water quality and environmental requirements. 

ACKNOWLEDGMENT

The development of the Port of New York/New Jersey water level and current nowcast/forecast 

model system has been carried out in the Coast Survey Development Laboratory (CSDL) of 

NOS=s Office of Coast Survey under the leadership of CSDL=s Chief Dr. Bruce Parker. Dr. 

Parker suggested the development of the nested grid model in resolving detailed current patterns 

and structure in the Kill Van Kull. The second author, Manchun Chen, while a visiting scientist 

at CSDL from the National Marine Data Information Service (NMDIS) of the Peoples Republic 

of China=s State Oceanographic Agency, developed the nested grid model coupling technique. 

We thank Dr. Leo Oey of Princeton University for providing guidance in the model nesting 

technique development. Dr. Frank Aikman, Chief of CSDL=s Marine Modeling and Analysis 

Programs (MMAP) has provided valuable oversight and review of the project. His critical report 

review is acknowledged. Dr. Aijun Zhang, also a visiting scientist from NMDIS, is 

acknowledged for his assistance in performing many model sensitivity experiments.
REFERENCES

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Chen, J., W. Shaffer, and S. Kim, 1993. A forecast model for extra-tropical storm surge. 

Advances in HydroScience and Engineering. Vol. 1, pp. 1437-1444. 

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Chesapeake Bay Operational Forecast System (CBOFS). NOAA Technical Report, NOS COOPS 0021, NOAA/NOS, 33p. 

Kim, S.-C., J. Chen, and W.A. Shaffer, 1996. An operational forecast model for extratropical 

storm surges along the U.S. east coast. Preprints Conference on Coastal Oceanic and 

Atmospheric Prediction, Atlanta, Amer. Meteor. Soc., 281-286. 

National Ocean Service (NOS), 1999. NOS Procedure for Developing and Implementing 

Operational Nowcast and Forecast System for PORTS, NOAA Technical Report, NOS COOPS 0020, NOAA/NOS, 33p. 

Wei, E. and M. Chen, 2001. Hydrodynamic Model Development for the Port of New York/New 

Jersey Water Level and Current Nowcast/Forecast Model System , NOAA Technical Report,

NOS CS 012, NOAA/NOS, 46p.