Posted: 3:50 pm Sunday, August 2nd, 2009

August marks the real start of hurricane season 

By Eliot Kleinberg

August is here, and storm watchers know what that means. Now is when the hurricane season really starts.

Click on the image for full-sized infographic

Click on the image for full-sized infographic

The season runs from June 1 to Nov. 30, and hurricanes have formed in every month except February.

But the months of August, September and October have accounted for more than 8 in 10 of the 600-plus hurricanes recorded since 1866.

Those three months account for about 95 percent of all “major” hurricanes, those with top sustained winds of at least 111 mph.

And the six weeks starting around mid-August have generated more than half of all recorded hurricanes.

The misleading calm during the first two months of hurricane season is a period forecasters sometimes call the “preseason.” It averages only one hurricane every other year. Forecasters worry that will lull people in strike zones.

This is the first year since 2004 in which no storm developed somewhere in the Atlantic basin before the end of July. And the 2004 season had been only the third in 15 years.

But the tropics made up for lost time in 2004, generating 15 storms — the historical average is about 10 — with four slamming Florida between early August and late September.

That had never happened before in Florida, and not in any state since Texas in 1886.

Two of those, Frances and Jeanne, are well known to residents of Palm Beach County and the Treasure Coast.

The reasons we’re approaching the height of the season:

— Water in the Caribbean Sea and Atlantic Ocean, which provides the energy for storms, is at its warmest.

— Wind shear, the difference between high and low winds, which tends to “kneecap” storms, is at its weakest.

— Lower levels of the atmosphere are loaded with moist air.

— And conditions are best for the powerful tropical waves to form off the African coast and then have the warm water of the central Atlantic Ocean to fuel them as they move toward North America.

By late October, ocean temperatures are beginning to drop and cold fronts start pushing from the northern regions, increasing wind shear.

One encouraging sign for this year: El Niño has returned. Scientists say it tends to limit the formation of tropical storms and hurricanes in the Atlantic.

Limit, but not necessarily eliminate.

Relatively quiet seasons still can generate storms.

And as Tropical Storm Fay showed last year, inundating much of the Treasure Coast, a storm doesn’t need to be a monster to do a lot of damage.

Meanwhile, the bookies will get busy again later this week.

On Aug. 4, the Colorado State University team of William Gray and Phil Klotzbach will update its June 2 forecast, which had called for 11 named storms — tropical storm or greater — along with five hurricanes and two major hurricanes.

And on Aug. 6, the National Oceanic and Atmospheric Administration will update its May 21 prediction of nine to 14 named storms, four to seven hurricanes, and one to three major hurricanes.

The historical average is 11, six and two.

While the various prognosticators never try to guess how many storms, if any, will strike land, or where, the Colorado State team gives a 28 percent chance of one striking somewhere on the U.S. East Coast, including peninsular Florida, compared with a historical average of 31 percent. Not necessarily Florida, just somewhere between Maine and Key West.

What about the next month or so?

Hurricane forecasters say they can’t even be certain about next week.

While the arrival of El Niño provides hints about the rest of the season, “We can’t make any definitive statement that it will be a slow season or will start ramping up as soon as we get into August and September,” National Hurricane Center specialist Robbie Berg said Thursday. 

“Even sometimes the day before something happens, we’re not sure,” he said. “For us to make a forecast two or three weeks down the road about what’s going to happen, we just can’t say.”