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Tropical Storm and Hurricane Forecasting Models

Forecasting Models

Hurricane Ike Forecast Models, September 9, 2008 ... Courtesy of WeatherUnderground
Hurricane Ike Forecast Models, September 9, 2008
Courtesy of Weather Underground

The term "forecast model" refers to any objective tool used to generate a prediction of a future event, such as the state of the atmosphere. The National Hurricane Center (NHC) uses many models as guidance in the preparation of official track and intensity forecasts.

Forecast models vary in structure and complexity. They can be simple enough to run in a few seconds on an ordinary computer, or complex enough to require a number of hours on a supercomputer.

Dynamical models, also known as numerical models, are the most complex and use high-speed computers to solve the physical equations of motion governing the atmosphere.

Statistical models, do not explicitly consider the physics of the atmosphere but are based on historical relationships between storm behavior and storm-specific details such as location and date.

Statistical-dynamical models blend both dynamical and statistical techniques by making a forecast based on established historical relationships between storm behavior and atmospheric variables provided by dynamical models. Trajectory models move a tropical cyclone (TC) along based on the prevailing flow obtained from a separate dynamical model.

Ensemble or consensus models are created by combining the forecasts from a collection of other models. more from the National Hurricane Center

Discussed herein are some of the more prominent weather forecasting models.

  • MRF (Medium Range Forecast) is a 28-level sigma vertical coordinate (terrain following) global spectral model with a triangular truncation of 126 waves.
  • AVN is the Aviation Run of the NCEP Medium Range Forecast (MRF) model.
  • BAM (Beta and Advection) Model follows a trajectory from the Aviation Run of the MRF model to provide a track forecast. The BAM model is run with shallow (850-700 hPa), medium (850-400 hPa) and deep (850-200 hPa) vertically averaged winds (BAMS, BAMM and BAMD, respectively).
  • LBAR (Limited area sine transform BARotropic) is a two-dimensional track prediction model which solves the shallow-water equations initialized with vertically averaged (850-200 hPa) winds and heights from the Aviation Run of the MRF global model.
  • GFDL (Geophysical Fluid Dynamics Laboratory) is a limited area baroclinic model developed specifically for hurricane prediction.
  • NOGAPS is the U.S. Navy's global spectral forecast model with 18 sigma levels, a triangular truncation of 159 waves, parameterizations of physical processes and a tropical cyclone bogussing scheme.
  • UKMET is the global forecast model run by the UK Meteorological Office. Similar to NOGAPS and the MRF model.
  • NHC90/NHC91 and CLIPER are statistical track forecast models. The predictors for CLIPER (CLImatology and PERsistence) include the initial latitude and longitude of the storm, the components of the storm motion vector, the Julian day and the initial storm intensity. The CLIPER forecasts are often used to normalize the output from other track models, and as a benchmark for evaluating track forecasting skill. NHC90 is a more general statistical model which uses the output from CLIPER in combination with vertically averaged (1000-100 hPa) geopotential heights from the Aviation Run of the MRF model as predictors. NHC90 was developed for the Atlantic and NHC91 was developed for the east Pacific.
  • SHIPS (Statistical Hurricane Intensity Prediction Scheme) is a statistical model used to predict wind intensity; it is based on climatological, persistence and synoptic predictors. The primary predictors include the difference between the maximum possible intensity (MPI) and the current intensity.
  • More details about track and intensity models (courtesy of NHC)
  • The naming conventions used by the Naval Research Laboratory (NRL) for the model scatter plot products:
    - Tropical cyclones for which the NHC issues advisories utilize numbers sequentially from 1 to 49.
    - Training messages are numbered 50-79
    - Test messages are numbered between 80-89
    - INVESTS are numbered between 90-99
    - Tropical cyclones which are forecast to develop by the UK Met Office model utilize the number 50. The tracks of these systems appear on the scatter plots for storm 50 as well as all storms between 80 and 99.