Storm-watch tool goes public

Jul 23, 2008

Watch hurricane center’s Web site as tropical waves grow stronger

Florida Today--July 23, 2008

Before 2004, few would have paid much attention to tropical waves peeling off Africa’s west coast.

Thirty hurricanes later, such disturbances elicit a bit more worry.

And this year, these early seeds of potential destruction grace the most prominent spot on the National Hurricane Center’s Web site, via a new tropical weather forecast graphic.

The center’s new tool for the first time gives the public the probability a tropical wave will develop into a cyclone. The outlook showed a 20 percent chance Tuesday that a tropical wave off Africa could grow into Edouard, the next name on the center’s list.

"I think this is a good step forward. This is actually our first time doing quantitative genesis forecasting for the general public," said Chris Landsea, science and operations officer for the National Hurricane Center in Miami.

About 60 to 70 tropical waves develop in the Atlantic region each hurricane season. Of those, only 10 percent become named storms. Storms get named when winds reach about 39 miles per hour. Hurricanes have winds at least 74 mph.

Still, these days, as hurricane season heats up, the curious and concerned home in on satellite images of disorganized cloud blobs in skies thousands of miles away.

On Tuesday, Tropical Storm Dolly was about 265 miles southeast of Brownsville, Texas. The storm was expected to strengthen and make landfall near the Texas-Mexico border late Tuesday or early today as a Category 1 hurricane.

The center issued a hurricane warning for Brownsville north to Port O’Connor, Texas, and a tropical storm warning from Port O’Connor to south of Galveston.

Also Tuesday, forecasters issued advisories on Tropical Storm Cristobal, centered about 450 miles south-southwest of Halifax, Nova Scotia.

The storm was not expected to make landfall, but officials issued high surf advisories and small craft advisories for coastal Rhode Island and Massachusetts.

Atlantic hurricanes typically start as weak tropical disturbances off Africa’s west coast. From the ocean surface to about three miles up, low-pressure air off Africa creates these "seedling" circulations.

Tropical waves, also known as African easterly waves, typically stretch north to south and travel east to west through the tropics, causing cloudiness and thunderstorms.

NOAA’s new experimental tropical wave tool measures cyclone probability as "low" (less than 20 percent), "medium" (20 percent to 50 percent) and "high" (greater than 50 percent). It looks ahead 48 hours and is updated three times daily.

The analysis looks at wind shear, atmospheric circulation and other factors that determine whether a storm will intensify.

Experts at the Hurricane Center are not afraid of being accused of crying wolf by drawing too much public attention to weak waves that so often peter out.

"There is the possibility that something could get over-hyped. But what we’re trying to provide is the best meteorological information possible," Landsea said.

Meanwhile, more than 3,000 miles from Florida, Edouard tries to get organized.

"Something that far east, of course, is not a threat at all for quite a long time," Landsea continued. "Of course, it would be of much more interest to the maritime community."