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  sci-tech > space > story pagecorner  

Conditions ripe for more hurricanes, satellites show

An artist representation of the SeaWinds satellite  

September 27, 1999
Web posted at: 4:06 p.m. EDT (2006 GMT)

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) -- Weather satellites operated by NASA and other agencies show conditions this fall that point to a hurricane alley in the Atlantic Ocean.

Now that communities from the Caribbean to the Gulf and East coasts of the United States have girded for, and sometimes been pounded by, tropical storms Harvey and Hurricanes Gert and Floyd, scientists are looking down the pipeline for the remainder of this hurricane season.

What they see is the meteorological equivalent of airplanes stacked on the runway waiting for take-off -- warmer than usual ocean temperatures with sea surface winds ready to suck up moisture and bring it down in a torrent of hurricane-strength rain and wind.

High wind speeds for Hurricane Gert and tropical storms Hilary and Harvey are shown in yellow in this Quicktime Video.
Quicktime Movie 576k
Nature's wrath

Timothy Liu, project scientist for a weather-watching NASA satellite called SeaWinds, said it was Floyd that finally prompted him to look for an explanation for this season's train of storms. Bathtub conditions at the surface of the Atlantic Ocean gave him his answer.

"As of a week ago, the ocean surface temperature was a few degrees higher than usual," Liu said, referring to data collected by a National Oceanic and Atmospheric Agency satellite.

"A temperature increase of 2 degrees is a big departure," he said. "The temperature of the ocean doesn't change much. Two degrees is a really big signal of the conditions."

Meteorologists believe the strength of Floyd, for instance, came from the warmth of the water below.

And the unusual sea temperatures will continue to create a clear corridor in the Atlantic Ocean for more storms to come.

Hurricanes thrive on water and wind -- specifically, warm ocean temperatures and vapor swirled up into the atmosphere by ocean surface winds.

The wind gains strength from the thermal energy of the ocean, eventually condensing vapors and circulating air fast enough to form high-speed wind and heavy rain.

The SeaWinds satellite, managed by NASA for the Jet Propulsion Laboratory, carries a scatterometer instrument that has measured those sea winds via microwaves bounced off the ocean's surface since the satellite's launch in June.

SeaWinds data combined with other weather-watching data, like NOAA's Advanced Very High Resolution Radiometer, paint a picture favorable to hurricanes this season, Liu said.

Warm conditions in the Atlantic and cooler conditions than normal in the Pacific Ocean also have forced the jet stream farther north and created a corridor for newly born hurricanes to move unimpeded from the ocean waters up the Atlantic coast, Liu said.

La Nina's influence

Colorado State University meteorologist William Gray said other factors played a part in Floyd's success.

Those factors include swings between El Nino -- abnormally warm waters in the Pacific Ocean -- and La Nina conditions in the equatorial Pacific Ocean.

This year's persistence of La Nina -- cool Pacific waters -- has worked in favor of hurricanes this season, he said.

El Nino enhances winds that work against Atlantic hurricanes. La Nina favors the growth of clouds that allow hurricane power to build.

Liu was more cautious about predicting hurricanes, saying the study of meteorology has far to go. Scientists still lack good models needed to make predictions, he said.

Models will come in part from data generated by SeaWinds and a satellite run jointly since 1997 by NASA and Japan's quasi-governmental space agency that can measure rain and temperatures inside storms.

The Tropical Rain Measuring Mission can see through clouds to the rain and wind inside a hurricane, unlike its predecessors, Liu said.

For now, the QuikScat instrument aboard SeaWinds remains inaccurate at extreme conditions until scientists finish calibrating it -- matching its readings against combined readings from other instruments, Liu said.

Liu's advice is for those on land is to prepare for more storms, especially since the Atlantic hurricane season got a late start this year. "The hurricane season still has one or two months to go," he said.

Time magazine contributed to this report.

Inland flooding -- not storm surge -- real killer, hurricane experts say
September 20, 1999
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September 19, 1999
Disaster declarations spread to New Jersey, Pennsylvania
September 18, 1999
Floyd's U.S. death toll at 34; floods may claim more
September 17, 1999
Weakened Floyd lashes New York, Northeast
September 16, 1999
Floyd spawns tornadoes en route to Carolinas
September 15, 1999
Floyd bashes Bahamas, takes aim at Florida
September 14, 1999

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