# Presentation: 372637

## Improved Statistical Intensity Forecast Models:

**A Joint Hurricane Testbed Year 2 Project Update **

- Mark DeMaria, NOAA/NESDIS, Fort Collins, CO
- John A. Knaff, NOAA/NESDIS, Fort Collins, CO
- John Kaplan, NOAA/AOML/HRD, Miami, FL

- Presented at the
- Interdepartmental Hurricane Conference
- March 7, 2007

## Outline

- Progress on JHT Project Goals
- New decay model in SHIPS
- Modified vertical shear calculation
-  * New problem in 2006 model
- Discriminant analysis version of the Rapid Intensity Index
- SHIPS and RII for the 2007 Season

## 2006 Operational Version of SHIPS

- Statistical-dynamical TC intensity prediction model
- 16 basic predictors
- atmospheric from GFS forecast fields
- oceanic from Reynold’s weekly SST
- climatology and persistence from ATCF input
- Correction for ocean heat content (Atlantic only) and GOES predictors
- previous JHT project
- Adjusted SST from Joe Cione cooling algorithm
- previous JHT project, Atlantic only
- Empirical decay equation over land

## 2006 Rapid Intensity Index

- Uses subset of SHIPS input most correlated with rapid intensity change
- Estimates probability of 25 kt increase in next 24 hours
- Original version used 30 kt threshold
- Atlantic and east Pacific versions
- Results included on SHIPS text output

## Goal 1. Modified Inland WindDecay Algorithm

- Kaplan and DeMaria (1994) inland decay developed for continental U.S. landfalls
- Too much decay for storms over islands and peninsulas
- Modified version where decay rate depends on fraction of storm circulation over land
- Reduces decay rate over islands and narrow land masses

## Atlantic SHIPS Improvements with New Decay Model (2001-2006)

*Note: No significant impact on East Pacific SHIPS*

***Goal 1 completed and has been in SHIPS since 2005***

## Goal 2: Improved Shear Calculation

- SHIPS uses NHC official track for center of shear calculation
- GFS vortex track can differ from NHC track
- Shear calculation uses large annulus to compensate (200-800 km)

## Example of NHC and GFS Track Mismatch96 h Forecast for Frances from 27 Aug 2004 12 UTC

**Example of NHC and GFS Track Mismatch****96 h Forecast for Frances from 27 Aug 2004 12 UTC**

**850 hPa                                                              200 hPa**

**G**

**G**

**O**

**O**

**G = GFS position****    ****O = NHC Position**

## New Shear Algorithm

- Track location of GFS vortex at 850 hPa
- Tracker finds location that maximizes 0 to 600 km symmetric tangential wind
- Checks for reasonable translational speeds
- Requires minimum cyclonic wind
- Symmetric circulation subtracted
- Starts from outer radius where symmetric circulation is cyclonic
- Subtraction radius decreases with height
- Shear calculation at NHC track position after vortex removed
- 0-500 km radius rather than 200-800 km annulus

## Example of Vortex Removal

**850 hPa**

**200 hPa**

**Total Wind                Symmetric Flow                   Residual**

## A New Predictor and Bad Old One

*New*: Time tendency of GFS mean 850 hPa tangential circulation
- 0 to 600 km average
*Old*: 850 hPa environmental vorticity
- 0 to 1000 km average
- Measures environment for small storms
- Measures storm circulation for large storm
- Inconsistent predictor with higher resolution GFS

## SHIPS With New Shear 

- Replace 200-800 km shear with 0-500 km shear (after vortex removal)
- Replace 850 hPa environmental vorticity with GFS vortex time tendency
- All 2006 cases re-run with operational input
- Logistic Growth Equation Model (LGEM) also tested with new shear
- Uses time stepping procedure instead of time averaging of predictors

## Forecast Impact 2006 Atlantic Re-runs

- Forecast Errors                                     Percent Improvement over
- 				        Operational D-SHIPS

## Forecast Impact 2006 East Pacific Re-runs

- Forecast Errors                                     Percent Improvement over
- 				        Operational D-SHIPS

## Goal 3: Improve theRapid Intensity Index 

- Operational version uses 6 scaled input parameters to estimate the probability of rapid intensification in the next 24 hours
- Improved version
- Use discriminant analysis to determine optimal weights for combining predictors
- Run in real time during 2006 season
- Also tested on larger sample in dependent mode
- RII Probabilities evaluated using Brier Skill Score

## 2006 RII skill

**2006 RII skill**

- Atlantic N=175 Nri=11 Probri = 6.3% (climo=12%)
- E. Pacific N=284 Nri=45 probri= 15.8% (climo=11%)

## RII Skill for the 2003-2005 developmental sample

**RII Skill for the 2003-2005 developmental sample**

- Atlantic N=846 Nri=115 Probri=13.6% (climo=12%)
- E. Pacific N=521 Nri=59 Probri=11.3% (climo=11%)

## Proposed Form of 2007 SHIPS and RII

- SHIPS
- Include new decay model
- Replace old shear with new one
- Replace 850 hPa environmental vorticity with 850 hPa GFS vortex circulation predictor
- Run LGEM version with new SHIPS predictors
- Additional changes
- Fix Central Pacific domain problem
- Additional GOES data quality control
- RII
- Re-develop discriminant analysis weights with 2006 case
- Run equal weights and DA version in 2007