# Presentation: 070686

## NOAA Hurricane Model Development at GFDL and the University of Rhode Island Morris Bender1, Timothy Marchok1,  Isaac Ginis2,  Biju Thomas2,  Richard Yablonsky21NOAA / Geophysical Fluid Dynamics Laboratory, Princeton, NJ        2University of Rhode Island, Graduate School of Oceanography, Narragansett, RI

**NOAA Hurricane Model Development at GFDL and the University of Rhode Island**** ****Morris Bender****1****, Timothy Marchok****1****,  Isaac Ginis****2****,  Biju Thomas****2****,  Richard Yablonsky****2**1NOAA / Geophysical Fluid Dynamics Laboratory, Princeton, NJ        2University of Rhode Island, Graduate School of Oceanography, Narragansett, RI

***Background***

***How a hurricane model forecast is made***

***Assessing the performance of the model forecasts***

***1. Gathering observations:  ***Before we can predict what the storm will do in the future, we need to gather as much data as possible on the current structure of the atmosphere and ocean.

_**Radiosondes:**_ These instruments are attached to weather balloons and transmit temperature, humidity, wind and pressure data at all levels of the atmosphere.  These balloons are launched globally twice a day.

_**Ocean:**_** **Ocean data are reported from fixed arrays of ocean buoys as well as from Airborne Expendable Bathythermographs (AXBTs).

_**Aircraft:**_** **Commercial aircraft regularly report weather data.  In addition, NOAA and Air Force “Hurricane Hunter” aircraft penetrate hurricanes in order to gather valuable data on the storms.

_**Satellites:**_** **Numerous satellites gather data on clouds, moisture and ground and sea surface temperatures.

- The **GFDL/URI** coupled hurricane prediction system originated as a research model developed in the 1970s at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL) located on the Princeton University Campus in Princeton, NJ.  Scientists developed the model to study the behavior of these powerful storms using the laboratory’s advanced supercomputers.

- In the mid 1980s, GFDL scientists began a 10-year effort to transform their research model into an operational tool for the National Weather Service.  Since becoming operational in 1995, the GFDL hurricane model has played a major role in improving hurricane prediction, resulting in a significant reduction in track forecast error. In addition, annual upgrades have been made to more accurately reproduce the meteorological and oceanographic factors that determine a hurricane’s motion and intensity. The current operational GFDL model consists of three computational meshes that are nested together with different grid-point spacing in each mesh.  The size of the outer mesh is ~ 5000 miles wide while the finest mesh, whose grid points are spaced only 5 miles part, covers a 325-square mile area. This area of fine resolution moves with the hurricane, keeping the storm centered in the middle of the innermost computational grid.

**Including the ocean’s impact**: In 1996, a collaboration began between scientists at GFDL and the University of Rhode Island (URI) to couple the atmospheric model to the Princeton Ocean Model. This coupling enables the model to reproduce the cooling of the ocean surface beneath the hurricane, which has an important impact on the hurricane intensity.  The GFDL/URI fully-coupled hurricane-ocean prediction system became operational in 2001.  The research group at URI has also made important contributions towards improving the air-sea fluxes in the GFDL model.

- GFDL and URI scientists have continued to transition the latest research advancements into the operational GFDL Hurricane Model, and this  has resulted in a steady reduction in forecast track error throughout the last decade.
- The figure to the left shows a comparison of the 12-year trend of the 3-day track forecast errors for the GFDL Hurricane Model and the official forecast issued by the National Hurricane Center.

- This figure compares the average track forecast errors in the Atlantic Ocean basin during the past 4 hurricane seasons for the most reliable computer models available to the National Hurricane Center.
- The GFDL Hurricane Model had the most reliable track guidance with the smallest track forecast errors.

- Until recently, even the most sophisticated computer models were unable to provide skillful forecasts of changes to a hurricane’s intensity.  However, the latest upgrades to the GFDL model have led to significant improvements in hurricane intensity forecasts by better representing the atmospheric and oceanic physical processes critical for intensity prediction.
- The figure to the left shows that in 2006, for the first time ever, the GFDL Hurricane Model produced hurricane intensity forecasts that had smaller average errors than those from the National Hurricane Center’s official forecasts.

***Hurricane track forecast guidance***

***Hurricane intensity forecast guidance***

_**Surface:**_** **At thousands of weather stations across the globe, observers report weather conditions every hour.

***2. Organizing the  observations:  ***Supercomputers at the National Weather Service use complex methods to process the data and create a 3-D depiction of the atmosphere and the ocean.

***3. Making the forecast:***  The forecast model uses the 3-D depiction of the ocean-atmosphere system as its starting point.  The model is then “run”, or integrated, out to 5 days in the future.  The supercomputer is needed for this since updated values for all variables must be computed at every computational point in the horizontal and vertical directions.  That’s roughly 1.8 billion new data values computed every minute.

***4. Interpreting the results:***  Computer model forecasts can vary from one “model run” to the next (see figure above).  Therefore, a critical step is interpretation of the model results by forecast specialists at the National Hurricane Center.   Forecasters can identify strengths and weaknesses in model forecasts so they can provide the public with the best guidance for an approaching storm.

***Contact Information:***

**Morris.Bender@noaa.gov**

**Timothy.Marchok@noaa.gov**

**iginis@gso.uri.edu**

**ryablonsky@gso.uri.edu**

**b.thomas@gso.uri.edu**

- This model was able to reproduce the features that are important in a hurricane. These include the inflow of low-level air into the hurricane’s inner core region; the supply of the storm’s energy from the evaporation of water from the ocean surface; updrafts of warm, moist air that feed thunderstorms in the core region of the storm, which help to intensify the hurricane; and the outflow of cooler, drier air at upper levels of the troposphere.

***250 feet below the ocean’s surface:*** During Hurricanes Katrina and Rita, deep warm water in the Loop Current and a Loop Current eddy was located under the storm tracks, which allowed these storms to reach Cat-5 intensity over the Gulf of Mexico.  These ocean features are accounted for in the GFDL/URI coupled hurricane model.

***Hurricane-ocean interaction:*** A hurricane affects its own intensity by interacting with the ocean. The hurricane churns the water beneath it, bringing cooler water up to the sea surface from below and leaving a “cold wake”. The cooler the water it brings up, the less fuel the hurricane has. When warm surface waters are shallow (left), cold water reaches the sea surface, greatly diminishing the hurricane’s intensity. Over deep warm waters (right), hurricanes tend to be more powerful because the ocean surface cooling is significantly less.