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Things People Use to Find Hurricanes
- The first weather satellites were launched in the early 1960s; one of their earliest missions was to scan the oceans for tropical development and thus prevent unexpected hurricane landfalls. A classic early case of satellite success was detecting Hurricane Camille in 1969. This storm formed in the southern Gulf and intensified rapidly as it sped toward the Mississippi coast. Had it not been for the weather satellite, the death toll from this Category 5 hurricane (winds exceeding 155 mph) would have been far greater.
Twenty-first century weather satellites are far more sophisticated than the early versions; on-board sensors detect clouds and moisture day and night, and they can interpret wind fields and temperatures as well. They can even measure sea surface temperatures in advance of the storm, which helps predict whether the storms will strengthen or weaken.
Radar Near Coastline
- Hurricane Isabel as seen on radar near the U.S. East Coast in 2003Getty Images/Getty Images News/Getty Images
Weather radar is another important tool for hurricane detection. Satellite imagery provides a rough idea of the storm's circulation and intensity. When the storm gets within 200 miles of the coast, the radar can directly measure precipitation bands and wind speeds within them. It's common to see on your local TV weather broadcast a radar image of a hurricane making landfall. The classic "hole" in the middle of the hurricane as depicted on radar allows a precise track of the storm's center, or eye, and direction of movement. The radar data enhances a forecaster's skills at predicting inland flooding, storm surge and wind speeds. All of these will factor into evacuation planning, emergency response and bulletins released to the public.
National Weather Service Doppler weather radars now cover virtually the entire U.S. coastline. Hurricanes often produce tornadoes, and the Doppler units allow detection and warning for these as well.
- Air Force reconnaissance flights have been flying directly into hurricanes since the late 1940s. Hurricanes are often first spotted on satellite well out of the range of weather radar -- sometimes over a thousand miles from the nearest land mass. The aircraft penetrates the storm in a crisscross pattern while gathering measurements from on-board radar, pressure, temperature and dew-point sensors.
A "dropsonde" is a special sensor package the plane releases while in the eye of the hurricane. It send back a stream of data as it falls slowly toward the ocean surface on a parachute.
Reconnaissance flights allow precise measurement of the most important indicator of hurricane intensity -- the central pressure. A rising pressure will point to a weakening storm while falling pressure signals higher winds and a more intense hurricane taking shape.
- Barometers measure surface pressure and anemometers measure wind speed and direction. A steady drop in pressure, increasing wind and long swells coming in from the ocean would alert a meteorologist even without any other data. The Galveston hurricane might have had a far lesser human toll had information from Cuba about a great storm with low pressure made its way to the Texas city by the sea.
Wind speed and direction and surface pressures are used to pinpoint the eye once the storm makes landfall and to classify it for damage potential. These data are used together with satellite and Doppler radar information in the 21st century.