WHAT ARE THE HURRICANE TRACKING MODELS
                                                                 

      
            AND HOW DO THEY FORECAST?                            

                                                                 

    
    The National Hurricane Center (NHC) in Miami,
Florida is a part of the National Weather Service, under the
National Oceanic and Atmospheric Administration, an agency of
the U.S.Department of Commerce. The NHC tracks tropical cyclones
from the tropical depression stage through the hurricane stage
over the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico and
Eastern Pacific Ocean and makes predictions of the future
position and intensity of the cyclones.
                                                               
To forecast the track and intensity of tropical
cyclones, NHC uses mathematical computer models. These models
represent the tropical cyclone and its environment in a greatly
simplified manner. Computers running these models can forecast
the future motion and intensity of a cyclone. Hurricane
forecasters then interpret model results to arrive at a final
track and intensity forecast, distributing it to the public in
the form of advisories.


The mathematical models used at NHC are of three basic
types:Statistical, Dynamical or Combination (Statistical and
Dynamical together). Statistical models forecast the
future by using current information about the hurricane and
comparing it to historical knowledge about the behavior of
similar tropical cyclones. The historical record for storms over
the north Atlantic begins in 1871, while the record for storms
for the east Pacific extends back to 1945. Dynamical models work
differently. They are designed to use the results of global
atmospheric model forecasts in different ways to forecast
tropical cyclone motion and intensity. Global models take current
wind, temperature, pressure and humidity observations and make
forecasts of the actual atmosphere in which the cyclone
exists.
                                                                
Because of their mathematical simplicity, dynamical models
ignore the behavior of historical storms. Combination models,
however, can be constructed to capitalize on the strengths
of each.
                     
Because of their simplicity, statistical models were designed
first for tropical cyclone forecasting in the late 1960's. In the
early seventies, combination models were developed as global
models began making forecasts in tropical regions. As computers
became more powerful, global models improved and pure dynamic
models are beginning to dominate the accuracy race. This is
particularly true when tropical cyclones approach data-rich
regions close to the continents where the state of the
atmospheric environment is adequately observed and
well-known. Over oceanic areas, far removed from land,
combination models are still the best performers.
                                                                
            
National Oceanic and Atmospheric Administration
National Weather Service/National/Hurricane Center
                                                           
November 1993
                                                                 
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