Tropical Twisters - Hurricanes: How they work and what they do.

Why do Hurricanes Move?

Hurricane Howard Hurricanes are "steered" by the prevailing wind currents that surround the storm from the surface to 50,000 feet or more. The storms move in the direction of these currents and with their average speed. The movement of a hurricane affects the speed of the winds that circulate about the center. On one side of the storm, where the circulating winds and the entire storm are moving in the same direction, the wind speed is increased by the forward movement of the storm. On the opposite side of the storm, the circulating wind speed is decreased by the forward motion. In the Northern Hemisphere, the right side of a hurricane, looking in the direction in which it is moving, has the higher wind speeds and thus is the more dangerous part of the storm. The average tropical cyclone moves from east to west in the tropical trade winds that blow near the equator. When a storm starts to move northward, it exchanges easterly winds for the westerly winds that dominate the temperate region. When the steering winds are strong, it is easier to predict where a hurricane will go. When the steering winds are weak, a storm seems to take on a mind of its own, following an erratic path that makes forecasting very difficult.

The major steering wind influence of most U.S. hurricanes is an area of high pressure known as the Bermuda High. This high pressure dome is over the eastern Atlantic Ocean in the winter, but shifts westward during the summer months. The clockwise rotation of air associated with high pressure zones is the driving force that causes many hurricanes to deviate from their east-to-west movement and start northward. Sometimes this is favorable: huricanes never reaches the shore, and blow out into the Atlantic Ocean. Other times, hurricanes south of the U.S. are steered northward directly towards the coastline.

Because Hurricane movement can be very erratic, scientists have increasingly been called to track them. NASA has been on the forefront on the design, development and deployment of Earth remote sensing spacecraft design to do just this.

GOES - I/M Missions

Over the past 30 years scientists have stated a need for continuous, dependable, and high-quality observations of the Earth and its environment. The new generation Geostationary Operational Environmental Satellites (GOES I through M) provide half-hourly observations to fill that need. The instruments on board the satellites measure atmospheric temperature, winds, moisture, and cloud cover.

GOES satellte

The GOES I-M series of satellites is owned and operated by the National Oceanic and Atmospheric Administration (NOAA). NASA manages the design, development, and launch of the spacecraft. Once the satellite is launched and checked out, NOAA assumes responsibility for it.

Each satellite in the series carries two major instruments: an Imager and a Sounder. These instruments acquire high resolution visible and infrared data, as well as temperature and moisture readings from the atmosphere. They continuously transmit this information to ground terminals where it is processed for rebroadcast to primary weather services, both in the US and around the world.

For more information about GOES visit their website.

Updated: January 22, 2003
Hurricane Andrew
The following movie shows Hurricane Andrew move from the Atlanic Ocean to the Gulf of Mexico in 1992.

1909 Was a Good Year for Hurricanes
Out of 12 tropical cyclones in 1909, four were hurricanes. On July 20th, a hurricane passed directly over Velasco, TX. There, the calm center lasted 45 minutes, and was followed by devastating winds which destroyed half of the town. Later, a very violent hurricane raked Haiti and entered the Yucatan Channel on August 25, causing an enormous loss of life and property. As the storm approached Mexico, it caused gales and tremendous waves along the Texas coast. Unofficial estimates placed the Mexican death toll at 1,500. On September 20, another intense hurricane crossed the middle Gulf Coast. A wide portion of the Louisiana coast was inundated, and about 350 lives were lost. The loss of life from these hurricanes was great in 1909 because warnings were inadequate; the same storms today would create great havoc but probably kill far fewer people, thanks to improved early warnings.

Find out more about Hurricanes.

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