wpostServer: http://css.washingtonpost.com/wpost2

Most Read: Local

Posted at 11:26 AM ET, 04/06/2011

Colorado State team predicts very active hurricane season; heightened U.S. landfall risk


Colorado State’s hurricane forecasting team of Dr. Phil Klotzbach (left) and Dr. William Gray (right) (Colorado State University)
The team of hurricane forecasters at Colorado State University (CSU) announced today that they expect the upcoming Atlantic hurricane season (spanning June through November) to be nearly twice as active as the average season (175 percent of normal). Specifically, they are calling for 16 named storms, nine hurricanes and five major hurricanes with sustained winds of 111 mph or greater.

Significantly, the team - in its 28th year of making these predictions - is calling for markedly elevated chances for landfalls in the United States.

“Except for the very destructive hurricane seasons of 2004-2005, United States coastal residents have experienced no other major landfalling hurricanes since 1999,” said vet­eran CSU forecaster Dr. William Gray. “This recent 9 of 11-year period without any major landfall events should not be expected to continue.”

The team provided the following probabilities for a major hurricane landfall on U.S. soil:

- A 72 percent chance that at least one major hurricane will make landfall on the U.S. coastline in 2011 (the long-term average probability is 52 percent).

- A 48 percent chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida Peninsula (the long-term average is 31 percent).

- A 47 percent chance that a major hurricane will make landfall on the Gulf Coast from the Florida Panhandle west to Brownsville (the long-term average is 30 percent).

For the mid-Atlantic region (region 9 on this map ), spanning northeast North Carolina through northern New Jersey, the team projects a 14.9 percent chance of 1 or more named storms making landfall in the region compared to just an 8.6% chance in an average year. The probability of a hurricane is 5.6 percent (compared to 3.2 percent on average). The chance of a major hurricane striking the mid-Atlantic (which hasn’t happened since we’ve had reliable observations) is less than 0.1 percent.

Farther south, from the North Carolina outer banks into southern South Carolina, they indicate a 61% chance of a landfalling storm (and 45% chance of a hurricane), compared to 40% on average (29% for a hurricane).

You can explore landfall probabilities assessed by the CSU team at the Landfalling Hurricane Probability Project website.

The team’s forecast for heightened activity is based primarily on these two factors:

1) Unusually warm tropical Atlantic sea surface temperatures combined with near-average Pacific sea surface temperatures (related to a weakening La Nina)

2) That we are in a multi-decadal period (since 1995) of enhanced Atlantic hurricane activity, expected to continue another 10-15 years.

When looking back at past years with similar oceanic and atmospheric features to this year, the CSU team identified five years with similar characteristics: 1955, 1996, 1999, 2006, and 2008. All except 2006 were very active hurricane seasons.

Although far from perfect, CSU forecaster Dr. Phil Klotzbach says these April-issued outlooks have shown “marked improvement” in recent years, due to advances in predicting El Nino and La Nina.

“By April,ENSO [La Nina and El Nino] forecasts have gotten quite a lot better ... the last three years have been pretty good,” he said. “As we get new data, and new understanding of what’s going on, we see improvements.”

The biggest wild card in CSU’s outlook is what happens with La Nina, which is currently weakening. Klotzbach said CSU modestly downgraded its preliminary outlook (issued in December) in light of predictions that the La Nina, which favors storm activity in the Atlantic, will fade away.

CSU will revise its outlook again in June, by which time the forecasts have reasonably good skill, Klotzbach said.

CSU’s predictions for 2011 are very similar to AccuWeather’s which were released last week. AccuWeather is forecasting 15 named storms,eight hurricanes and three major hurricanes. AccuWeather also emphasized the elevated U.S. landfall risk in its outlook.

Last year, CSU’s prediction for Atlantic tropical activity came close to veryifying. It predicted an active season with 15 named storms and 19 occurred.

Irrespective of the seasonal forecast, the CSU team emphasized storm preparedness.

“It is recommended that all vulnerable coastal residents make the same hurricane preparations every year, regardless of how active or inactive the seasonal forecast is,” Klotzbach said. “It takes only one landfall event near you to make this an active season.”

By  |  11:26 AM ET, 04/06/2011

Categories:  Tropical Weather, Latest

 
Read what others are saying
     

    © 2011 The Washington Post Company