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Busy Atlantic Hurricane Season Brings Review of Forecasting Skills - 2004-09-17

It has been a rough weather week in the Caribbean and Eastern United States. Hurricane Ivan - the third major hurricane to strike the region in the past several weeks - tore across several island states, and battered the west end of Cuba on its way into the Gulf of Mexico packing 260 kilometer-per-hour winds. Early Thursday, Ivan slammed into the Alabama and Florida coasts of the southern United States, where it wreaked havoc on coastal communities. By week's end, the once-powerful hurricane had weakened to a tropical depression, but not before dumping torrential rains and spawning tornadoes across the American south. And more severe storms are on the way.

Ivan is the 10th tropical storm or hurricane this year to roar out of the Atlantic. A tropical storm is assigned a name when it has sustained winds of greater than 63 kilometers per hour; it becomes a hurricane at around double that speed. And with hurricane season at its midpoint, more storms are expected through November.

The convention of naming storms began in the 1950s, at first using only women's names. In 1979, the United States and 24 other countries agreed on an international system of identification, which alternates male and female names in alphabetical order using the Roman alphabet. The list is maintained and operated by the World Meteorological Organization, with lists prepared ahead of time and used in a six-year rotation.

The fact that we give names to these ocean-born storms suggests how we sometimes think they have minds of their own. Names also suggest our respect for the hurricanes' power and scale. Hurricanes are huge. Ivan at one point stretched more than 480 kilometers from Florida to Louisiana.

"You see we aren't taking any chances. We will be in another state when [the storm] gets here," said one man from the Florida coast, who took the warnings seriously and boarded up his house before heading inland.

People living on or near the coast are always most vulnerable to hurricanes. Ivan's powerful winds ripped off roofs, flattened mobile homes, uprooted trees and brought down power lines serving tens of thousands of people. William Gray is a professor of atmospheric science at Colorado State University. He looks at weather conditions on a global scale to make a series of hurricane forecasts prior to the start of the season. Professor Gray's team accurately predicted that 2004 would be a more active Atlantic hurricane season than in past years. To understand why, Professor Gray says, we need to look closely at the storm incubation area, thousands of kilometers away. "It you look at West Africa and the Sahara Desert to the North. And, it is very warm there and we have special conditions. As you go pole-ward it gets warmer. In most places of the globe you go pole ward and it gets colder. So, the winds and the wind sheer and things there are favorable for forming these disturbances or waves that move off West Africa. Now as they move into the Central Atlantic if the vertical wind sheers and the sea surface temperatures and the surface pressures are favorable, you will tend to get these systems forming into storms," he says.

On average, 60 of these waves originate in the West African Atlantic each hurricane season. Higher water temperatures and circulating air turn the waves into storms and hurricanes. And experts are predicting a gradual rise in storm intensity and rainfall from global warming. William Gray says there is no way to stop or slow a hurricane once it begins its journey. "You just adjust. There is really nothing we can do now to alter these storms or change them. You just have to have warnings out and encourage people that build homes along the coast to spend a little more money to make [their homes] a little bit more wind resistant. And [we should] not have people living in such low-lying lands that can be flooded.

Discussing how far scientists come in the prediction of hurricanes, he says "there has been great improvement, especially with the satellite. The satellite has been a marvelous thing in that it sees the weaker storms as they begin to form. So, we don't miss some of these weaker systems as we did in the pre-satellite days. Now, once they are formed, the satellite gives a good estimate on how intense the storm is and they have a new jet plane that tries to fly around these storms [that can] get the steering currents to determine where the storm is going. So there has been an improvement in the last decade or two in the track prediction, where the storm goes. But in terms of telling what the intensity of the storm whether it is going to be one, two or three days in the future, there hasn't been much improvement there."

I think that one of the things that could be done [to improve forecasting] that isn't being done now is to fly jet planes through the center of storm in the upper troposphere. We don't have upper tropospheric measurements around the center. We used to, back in the late [1950s], with some Airforce B-47s that used to fly into the center, but that was discontinued long ago."

William Gray and a team of scientists at Colorado State University make advanced seasonal predictions based on ocean temperatures and atmospheric conditions. These studies alert planners that a powerful storm may be on the way. Such early warnings can and do help save lives and loss of property.