Tropical cyclone track forecasting

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.

The methods through which tropical cyclones are forecast have changed with the passage of time. The first known forecasts in the Western Hemisphere were made by Lt. Col. William Reed of the Corps of Royal Engineers at Barbados in 1847. Reed mostly utilized barometric pressure measurements as the basis of his forecasts. Benito Viñes, S.J., introduced a forecast and warning system based on cloud cover changes in Havana during the 1870s. Forecasting hurricane motion was based on tide movements, as well as cloud and barometer changes over time. In 1895, it was noted that cool conditions with unusually high pressure preceded tropical cyclones in the West Indies by several days. Before the early 1900s, most forecasts were done by direct observations at weather stations, which were then relayed to forecast centers via telegraph. It was not until the advent of radio in the early twentieth century that observations from ships at sea were available to forecasters. Despite the issuance of hurricane watches and warnings for systems threatening the coast, forecasting the path of tropical cyclones did not occur until 1920. By 1922, it was known that the winds at 3 kilometres (9,800 ft) to 4 kilometres (13,000 ft) in height above the sea surface within the storms' right front quadrant were representative of a storm's steering, and that hurricanes tended to follow the outermost closed isobar of the subtropical ridge.

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