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.