Atlantic Hurricane Factory Primed

Aug. 22, 2006 — The latest space-based measurements of Atlantic Ocean surface temperatures have revealed a wide swath of hot water ready to supercharge any storms that form there — if a few other things line up as well.

In recent weeks the water temperatures have risen significantly from the Cape Verde Islands off northern Africa, all the way west to the Gulf of Mexico.

A broad expanse of surface waters have hit the magic 82 degrees Fahrenheit (28 C) mark, which hurricane experts say is prerequisite for the hurricane factory to kick on.

"We’re a little bit cooler than this time last year, but it’s still warm enough," said NASA oceanographer David Adamec.

Satellite microwave images of Earth’s oceans from this year and last show differences that might lead to a less stormy Atlantic hurricane season, he said. Or not. That’s because Mother Nature still has to flip on a few more switches to get the factory churning out storms.

One thing that always helps a fledgling hurricane is for the layer of warm surface water to be relatively deep, said Adamec. Greater volume of that bath-like water means more actual heat is stored there – which can be tapped by storms.

More warm water existed this time last year, especially off North Carolina's Cape Hatteras where the Gulf Stream veers out to sea. Adamec pointed out the differences in images collected by Japan’s Advanced Microwave Scanning Radiometer flying onboard NASA's Aqua satellite.

"There’s a deep dome of warm water under this," explained Adamec, pointing to a region of false-colored red, warmer Gulf Stream water.

A switch that needs to be flipped "off" for the hurricane factory to function is wind shear. That’s the differences in the speed and direction of winds at different elevations.

If wind shear is high in the atmosphere over the equatorial Atlantic, off come the heads of tropical storms and they die. That’s what happened to tropical storm Chris — the first big storm out of the factory this season — said NASA hurricane researcher Scott Braun.

"The precipitation moved to the south, and strong north winds at upper levels basically tore the storm apart," said Braun of Chris’ demise.

Still, with all these clues to what makes the hurricane factory work, neither Braun or Adamec are ready to say what’s in store this season.

"All this changes with day-to-day weather," Adamec said. And historically the most rapid increase in storm number is the two weeks leading up to September 10 – the peak of the hurricane season. They then usually taper just as fast.

In 2005 and 2004 the hurricane season got an early start, said Braun. That might give people a false sense of a quieter storm season this year, he said. This year the factory is revving up at a more normal rate, he said.

"It’s still early," said Braun. "Things are just getting started."