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2002 Atlantic hurricane season gears up

Hurricane Andrew struck the southeastern United States in 1992. It's rated the most expensive and destructive Atlantic hurricane to affect U.S. land to date.

(CNN) – The National Hurricane Center is bracing for a busier-than-usual storm season, continuing a trend of above-normal activity during six of the last seven seasons.

The prediction center estimates nine to 13 tropical storms will incubate in the warm Atlantic Ocean waters this hurricane season, which runs from June 1 until the end of November. Six to eight of them will develop into hurricanes, and between two and three of those storms will grow to be major hurricanes -- storms that pack wind speeds of greater than 111 mph -- the center said.

The NHC said the heightened storm activity is due to long-term climate patterns, including warmer waters in the Atlantic, air pressure and patterns of tropical rainfall.

The National Hurricane Center monitors the oceans and determines a weather disturbance is a tropical storm when it has winds above 39 mph. The agency also gives a tropical storm a name to make communication with the public easier. A tropical storm is upgraded to a hurricane when its winds climb higher than 74 mph.

A normal season averages 10 named storms, but last year, 15 named storms took shape in the Atlantic. None of those storms struck the United States. In fact, since 1999 when Hurricane Irene swamped Cuba and parts of Florida, a record 18 hurricanes have formed, all failing to make landfall in the United States.

The reprieve may be a fluke, said Max Mayfield, the National Oceanic and Atmospheric Administration's National Hurricane Center director.

"The respite in hurricane landfalls can be attributed partially to luck, and a persistent trough near the U.S. East Coast that helped steer away the storms," Mayfield said of last year's hurricane season.

Monster storm

Here are a Dropwindsonde station and airborne expendable bathythermograph station on one of the NOAA airplanes.

The number of hurricanes that develop each season does not mean that any of them will reach the U.S. coastline, NOAA experts said.

Hurricane Andrew's blustery force hit Florida and Louisiana in 1992, killing 26 people and racking up more than $40 billion worth of damage. The monster storm teetered on the brink of being ranked in the most severe level of hurricanes -- a category 5 on the Saffir-Simpson Hurricane Scale. The most destructive hurricane in U.S. history blew ashore in a below-average hurricane season.

In the 10 years since Andrew's destruction, the National Hurricane Center and NOAA have acquired improved computers, environmental satellites and have achieved a better understanding of global climate patterns necessary to track a storm's path and predict its severity.

One of the most cutting-edge pieces of hurricane tracking technology developed in 1997 is a hardy device dubbed the Dropwindsonde, said National Hurricane Center public affairs officer Frank Le Pore.

Just 3 inches wide and 2 feet in length, Dropwindsondes are capsules filled with instruments that are dropped from research jets as they fly into the massive storms. As the Dropwindsondes fall through the atmosphere at nearly 33 feet per second they beam vital information like wind speed, pressure, humidity and temperature back to the jet.

With the Dropwindsondes "you can really tell what the wind speed is at or near the ground," Le Pore said.

Dropwindsondes cost $550 apiece and are irretrievable once they've been dropped from the jet, but these devices give scientists a rare glimpse at conditions on the ground at the height of a storm. Prior to their development, the type of data Dropwindsondes provide literally were estimated visually, according to the NOAA Web site.

The spin factor

Even as scientists scramble to find better ways to track these monster storms, hurricanes continue to fascinate. Their deadly combination of tornadoes, high winds, storm surge and flooding kill thousands every year.

Hurricanes typically begin as lines of thunderstorms or areas of disturbed weather, said Le Pore.

"Storms start in shallower waters in the early part of the season. Once the sun has had time to beat on the water, to make it 80 degrees, a low pressure system forms," he said.

This "blob of disorganized weather" takes heat from the surface of the water and rises until it hits cold air. When the hot air is cooled it begins to descend again. Soon, this continual rotation becomes a vertical "conveyor belt of air," explains Le Pore.

The storm builds in strength vertically, but it also forms borders horizontally as the winds react to the "normal" air at its sides. The rotation of the Earth begins to whip the storm in a circular pattern, said Le Pore, and the storm begins to bloom as it spins and builds vertically and horizontally.

The strength of a tropical storm or hurricane can depend on how tightly the rotating storm clouds are formed around the center, or eye, of the storm.

"Spinning is one of the factors that makes a storm more vicious," he said.

Le Pore likens hurricanes to ice-skaters. When a skater spins with outstretched arms, the spin tends to be slow, even sloppy. If a skater keeps his arms tucked close to his body, the spin tends to be fast and sharp, he said. The same principle is true of a burgeoning storm system.