Now that's intense!
But while it rained frogs on shore, Isabel dumped even more surprises on hurricane scientists before it made landfall. Using new heavy duty instruments, researchers studied for the first time how warm ocean water and air interact to change the intensity (wind speed) of powerful, Category 5 hurricanes. Before now, scientists could only get the inside scoop on low-intensity storms. "No one's been able to make these kinds of measurements before, because the wind destroyed the instruments," says hurricane expert Peter Black of NOAA (National Oceanic and Atmospheric Administration).
A hurricane is born when ocean temperatures climb above 27[degrees]C (82[degrees]F) and the air is three to four degrees cooler. To even out this temperature difference, "the air is always pulling heat energy from the water surface," says Black. The ocean water evaporates (changes from a liquid to a gas) and gives its energy to the air--a process called air-sea transfer. As the warmed air rises, it stirs up the wind, cools, and condenses (opposite of evaporation) to form thunderclouds. As the air pulls heat from the ocean, the hurricane intensifies (see SW, Oct. 18, 2002).
Intensity is still the largest mystery in hurricane science. Scientists know how the transfer process works in tropical storms (winds of 39--73 mph). But not in raging storms like Isabel. "Different things happen in high winds than in low winds," says Black. His team will use the study's data to create a formula for predicting hurricane intensity. These predictions will help residents and emergency personnel prepare for a hurricane--and be on the lookout for raining frogs!
HOW BAD WAS IT ON A SCALE OF 1 TO 5?
The Saffir-Simpson Hurricane Scale is a rating used to give an estimate of possible property damage and flooding expected along a coast when a hurricane strikes land.
CATEGORY 1 (74-95 MPH)
Damage primarily to trees and unanchored mobile homes; some coastal flooding.
CATEGORY 2 (96-110 MPH)
Some damage to roofs, doors, windows, trees and shrubbery; flooding damage to piers.
CATEGORY 3 (111-130 MPH)
Some structural damage; large trees blown down; flooding near shoreline and possibly inland; mobile homes destroyed.
CATEGORY 4 (131-155 MPH)
Extensive damage to doors and windows; major damage to lower floors near shore; terrain may be flooded well inland.
CATEGORY 5 (MORE THAN 155 MPH)
Complete roof failure and some building failures; massive evacuation; flooding causes major damage to lower floors of all shoreline buildings.
SOURCE: NATIONAL WEATHER SERVICE; NATIONAL HURRICANE CENTER
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|Title Annotation:||Freeze Frame|
|Date:||Nov 17, 2003|
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