Published August 8, 2011
The National Oceanographic and Atmospheric Administration (NOAA) updated its official forecast for the 2011 hurricane season last week, saying that the number and intensity of storms this year could be somewhat greater than the agency’s National Hurricane Center predicted in May.
Why is a Hurricane Forecast Update Needed?
Exceptionally high sea-surface temperatures (the third-warmest on record) and a variety of atmospheric conditions that can combine to cause hurricanes, including the possibility of La Niña conditions, led NOAA to upgrade its earlier forecast.
"We expect considerable activity," said Gerry Bell, lead seasonal hurricane forecaster at NOAA's Climate Prediction Center in Washington, D.C., in an interview with the Associated Press. "There is absolutely no reason that people should be complacent. Now is the time people really need to make sure they have their hurricane preparedness plans in place."
NOAA now says there is an 85 percent chance of an above-normal hurricane season this year, and a 15 percent chance of a near-normal season. The agency says there is no expectation of a below-normal season. When NOAA issued its pre-season outlook in May, it said there was only a 65 percent chance of an above-normal hurricane season.
If the prediction proves accurate, 2011 would be the twelfth above-normal hurricane season since 1995.
The possibility of La Niña conditions developing could complicate things even more. La Niña is an unusual cooling of waters in the Pacific Ocean near the equator, which cuts wind shear over the Caribbean and the tropical waters of the Atlantic Ocean, making it easier for tropical storms to develop and grow in force.
According to hurricane forecasters at NOAA, La Niña conditions helped make the 2010 hurricane season one of the busiest on record with 19 names storms, including a dozen hurricanes.
The opposite El Niño effect, which warms Pacific waters near the equator and increases wind shear over the Atlantic and the Caribbean, impedes storm development and can help prevent hurricanes from forming.
What is the New Hurricane Forecast for 2011?
The new forecast calls for 14 to 19 named tropical storms (including the five that have already occurred), up from the 12 to 18 that were predicted in May. Tropical storms are named when their winds reach speeds of 39 mph (62 kph) or higher.
NOAA now expects seven to 10 of those named tropical storms to become hurricanes, with winds of 74 mph (119 kph) or higher, up from six to 10 in May. Three to five of those hurricanes could become major storms, with top winds of 111 mph (178 kph) or higher.
NOAA estimates a 70-percent probability for each of those ranges in 2011.
When is the Greatest Hurricane Danger?
The official hurricane season begins each year on June 1 and ends November 30, but the peak months for hurricanes are August through October.
"The atmosphere and Atlantic Ocean are primed for high hurricane activity during August through October," Bell told the AP. "Storms through October will form more frequently and become more intense than we've seen so far this season."
Hurricane Katrina, which devastated New Orleans and did considerable economic and environmental damage along the Gulf Coast in 2005, occurred in September. So did Hurricane Ike in 2008, the third-costliest hurricane ever to make landfall in the United States. Hurricane Wilma, the most intense tropical cyclone ever recorded in the Atlantic basin, occurred in October 2005. And Hurricane Andrew, the costliest hurricane in U.S. history prior to Hurricane Katrina, occurred in August 1992.
How Many Hurricanes Will Strike Land in 2011?
NOAA doesn’t offer a seasonal hurricane landfall forecast, because there is simply no way to accurately make such predictions. Where and when hurricanes strike land depends on daily weather patterns, which can’t be predicted far in advance.
“But remember that it only takes one storm hitting your area to cause a disaster, regardless of the overall activity predicted in this outlook,” the NOAA update says. “Therefore, residents, businesses, and government agencies, of coastal and near-coastal regions are urged to prepare every hurricane season regardless of this, or any other, seasonal outlook.”