Last May, the nation’s senior hurricane forecasters gathered in Bay St. Louis, Miss., to warn the nation that another active Atlantic tropical storm season was on the way. Less than four months later, Hurricane Katrina nearly washed the town away.
The long-range forecast issued by the National Oceanic and Atmospheric Administration in May called for up to 15 tropical storms, with as many as nine strengthening to hurricanes. Those numbers were updated in early August to 21 named storms, with as many as 11 reaching hurricane strength.
Even that outlook didn’t quite capture the scope of the season, nor were the forecasters able to know that the ground where they stood on May 16 would be under a 30-foot storm surge on Aug. 29.
“Driving along that beach road past those big yards and houses, it was impossible to imagine that the ocean could ever be over those houses,” said Gerry Bell, the lead meteorologist for hurricane outlooks at NOAA’s Climate Prediction Center. “Intellectually, you know it can happen, but I still couldn’t imagine what Katrina did.”
By mid-November, there would be a record-breaking 25 named tropical storms in the Atlantic basin _ including Delta, which formed Wednesday. The previous record was 21 in 1933. Thirteen of this season’s storms became hurricanes, and seven of those strengthened to “major” hurricane status with winds in excess of 111 mph.
“We had a very high confidence in our predictions for the level of activity for the season. We understand the climate patterns that control hurricane activity in the Atlantic very well, and we can monitor them and forecast from those patterns in a way that wasn’t possible even 10 years ago,” Bell said.
Those ingredients _ favorable winds carrying tropical waves off Africa, Atlantic sea-surface temperatures well above normal, lower vertical wind shear in the main hurricane development region across the tropics _ have all been in place fairly steadily every summer and fall since 1995, a season that brewed 19 tropical storms and marked the beginning of a new active period for hurricanes that forecasters say could go on for another 15 to 20 years. Nine of the past 11 hurricane seasons have seen above average activity.
The last time the climate of the Atlantic settled into such a pattern was during the 1950s and ’60s. That pattern was reversed from 1970 through 1994, which saw just three seasons with above-normal numbers of storms.
More storms don’t always mean more storms hitting the U.S. coastline, of course. Both the 2000 and 2001 seasons were above normal, but no hurricane-force winds affected the United States.
Yet as Colorado State University tropical forecasting expert William Gray started warning in 1996, “the lull will not continue indefinitely. The return of increased major landfalling hurricane activity should be expected within the next decade or so.”
Sure enough, the United States has returned to the hurricane crosshairs. Seven of the 13 major hurricanes that have formed in the past two seasons made U.S. landfall as major hurricanes.
Florida took hits from all three of the major hurricanes that came ashore last year, plus visits from two weaker storms. This year, the state endured two more tropical storms, plus hurricanes Dennis and Wilma.
Dennis first walloped Cuba before making landfall near Pensacola in July with winds in excess of 120 mph. Wilma, which crossed the state, struck Everglades City with winds in excess of 121 mph on Oct. 24 and may have actually gotten stronger as it moved over the Everglades.
Wilma made meteorological history as it rapidly intensified south of Cuba Oct. 18 into the strongest storm, in terms of atmospheric pressure (882 millibars), ever recorded in the Atlantic basin. Wilma, along with Rita and Katrina, also set a season record for Category 5 hurricanes _ those with winds above 155 mph. There had never been more than two storms that strong reported in any previous season.
But it was Katrina and the toll that hurricane inflicted from Louisiana to the Florida panhandle that did the most to reawaken the nation to the destructive power of tropical cyclones.
With an official death toll of 1,302 at last report and damage estimated at $100 billion, Katrina ranks as the most costly hurricane in U.S. history and the third deadliest, behind only the toll of the 1900 storm that killed an estimated 8,000 people at Galveston, Texas, and a 1928 hurricane that claimed 1,836 in south Florida.
Katrina produced some of the most specific, dire warnings ever issued by the National Weather Service. Even President Bush urged New Orleans and coastal residents to evacuate the day before the storm hit. Yet thousands remained in harm’s way, either because they thought they could ride out the storm, or because they lacked transportation to leave and clear plans on where to go.
Bell and other forecasters have some concern that when people heard reports that Katrina had “weakened” to top winds of 150 mph and was taking a track slightly east of New Orleans, they may have mistakenly thought they were dodging the bullet.
“A hurricane is not a point, and this one in particular was a huge storm with hurricane force winds extending out 120 miles, an eye wall that touched New Orleans on one side and Biloxi on the other. So the little changes that happen before landfall shouldn’t obscure the relevant information that this thing is about to clobber you,” Bell said.
Long-range forecasts, improved radar, buoys and instruments dropped from weather reconnaissance planes, and more sophisticated computer models have all boosted the ability of hurricane forecasters to plot the path and development of storms. But “knowing precisely where a hurricane will strike and at what intensity still cannot be determined even a few days in advance,” said Max Mayfield, director of the National Hurricane Center.
“The real message from this record season isn’t to fuss over the numbers or even how well we did on a particular forecast,” Bell said. “People need to know that they can be affected by hurricanes even if they live well inland, and they need to be prepared for not just one, but very possibly several storms in a season as long as we stay in this more active pattern.”
On the Net: http://www.nhc.noaa.gov
(Contact Lee Bowman at BowmanL(at)SHNS.com)