page_title: Tropical cyclone track forecasting
section_title: Forecast models
hierarchical_section_title: Tropical cyclone track forecasting / Forecast models
caption_attribution_description: English: Graphic showing spread in guidance, and failure of the guidance to pick up on Ernesto's more northerly course
context_page_description: Tropical cyclone track forecasting involves predicting where a tropical cyclone is going to track over the next five days, every 6 to 12 hours. The history of tropical cyclone track forecasting has evolved from a single-station approach to a comprehensive approach which uses a variety of meteorological tools and methods to make predictions. The weather of a particular location can show signs of the approaching tropical cyclone, such as increasing swell, increasing cloudiness, falling barometric pressure, increasing tides, squalls, and heavy rainfall.
  The forces that affect tropical cyclone steering are the higher-latitude westerlies, the subtropical ridge, and the beta effect caused by changes of the coriolis force within fluids such as the atmosphere. Accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will migrate during the life of a tropical system. Computer forecast models are used to help determine this motion as far out as five to seven days in the future.
context_section_description: High-speed computers and sophisticated simulation software allow meteorologists to run computer models that forecast tropical cyclone tracks based on the future position and strength of high- and low-pressure systems.  Combining forecast models with increased understanding of the forces that act on tropical cyclones, and a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades.  The addition of dropwindsonde missions around tropical cyclones in what are known as synoptic flow missions in the Atlantic Basin decreased track error by 15–20 percent. Using a consensus of forecast models, as well as ensemble members of the various models, can help reduce forecast error.  However, regardless how small the average error becomes, large errors within the guidance are still possible.  An accurate track forecast is important, because if the track forecast is incorrect, forecasts for intensity, rainfall, storm surge, and tornado threat will also be incorrect.
caption: Significant errors in track still occur on occasion, as seen in one of Ernesto's (2006) early forecasts.  The National Hurricane Center's official forecast is in light blue.
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