Track of Hurricane Charley, August 9-15, 2004
Courtesy of USGS based on data from the National Weather Service
How do we know which way a hurricane will go? Forecasters track hurricane movements and predict where the storms will travel as well as when and where they will reach land. While each storm will make its own path, the movement of every hurricane is affected by a combination of the factors described below.
Hurricanes are steered by global winds. These winds, called trade winds, blow from east to west in the tropics. They carry hurricanes and other tropical storms from east to west. In the Atlantic, storms are carried by the trade winds from the coast of Africa where they typically form westward to the Caribbean and North American coasts. When the trade winds are strong it is easier to predict where the storm will travel. When they are weak it's more difficult.
After a hurricane crosses an ocean and reaches a continent, the trade winds weaken. This means that the Coriolis Effect has more of an impact on where the storm goes. In the Northern Hemisphere the Coriolis Effect can cause a tropical storm to curve northward.
When a storm starts to move northward, it leaves the trade winds and moves into the westerlies, the west to east global wind found at mid-latitudes. Because the westerlies move in the opposite direction from trade winds, the hurricane can reverse direction and move east as it travels north.
High pressure systems can also affect the path of storms. In the Atlantic Ocean, the Bermuda High affects the path of hurricanes. When the storms are carried west by the trade winds, they are pushed north around the edge of the high pressure area.
Although these factors add up to a typical hurricane path that travels west and then bends poleward, there are other factors that affect a hurricane's path and complex hurricane tracks are common too. Forecasters use computer models to predict the path that a hurricane will follow but there is always some uncertainty. They can project where a hurricane will be a day in the future with much more certainty that they can project a week in the future. Predicting where a hurricane will make landfall is currently an area of active research.
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