Contact: Frank Lepore FOR IMMEDIATE RELEASE Stephanie Kenitzer 8/7/98
There is an increased likelihood of above-average tropical storm and hurricane activity over the North Atlantic during August-October 1998 in response to ongoing La Nina conditions, according to an outlook issued today by the Commerce Department's National Weather Service, with an increased likelihood of more hurricanes reaching major hurricane status.
D. James Baker, director of the National Oceanic and Atmospheric Administration, provided the outlook to representatives from the Federal Emergency Management Agency and Florida business and civic leaders during a FEMA-sponsored "Hurricane Damage- Prevention Roundtable" at Deerfield Beach, Fla.
Vice President Gore, FEMA Director James Lee Witt and Florida Governor Lawton Chiles were among those whom Dr. Baker addressed at the hurricane preparedness event. "We are very confident that the La Nina conditions that began developing earlier this summer will increase hurricane activity at the height of the season," said Dr. Baker. "Regardless of the predictions, we encourage residents to always be prepared."
The average number of systems reaching tropical storms, hurricane and major hurricane status during August - October is seven, five and two, respectively. During La Nina episodes, the continental United States oftentimes experiences more than usual land falling hurricane activity. The Caribbean region is also far more at risk of experiencing a hurricane during La Nina episodes than at other times.
"This outlook represents our confidence in the current La Nina predictions and the impact on hurricane activity," said Gerald Bell, research meteorologist at the Climate Prediction Center. "This is the first step in developing official predictions of seasonal hurricane activity. Much work remains to refine these outlooks for more details to guide emergency managers and other users on preparedness efforts."
The outlook should be used as a guide of overall expected activity for the Atlantic basin and does not give any indication of whether a particular locality will be impacted by a tropical storm or hurricane.
La Nina refers to cooler than average sea-surface temperatures across the eastern tropical Pacific. La Nina conditions are expected to strengthen during the next few months, and to remain in place at least through the winter.
Research conducted at Colorado State University by Professor William Gray has shown a distinct link between extremes in sea surface temperature conditions in the central and eastern tropical Pacific Ocean and hurricane activity in the Atlantic.
La Nina episodes contribute to hurricane activity by replacing westerly winds aloft with easterly winds. Since low level winds are almost always easterly at the surface, like wind direction through the depth of the atmosphere reduces variation of wind with height, also called "wind shear." Wind shear is an important factor controlling the organization of tropical thunderstorm activity, which ultimately leads to tropical storm and hurricane development. Although there are a number of different factors that affect the overall tropical storm activity in a given hurricane season, reduced vertical wind shear is a necessary condition for enhanced hurricane activity.
The hurricane season for the Atlantic basin, which includes the North Atlantic Ocean, Caribbean Sea and Gulf of Mexico, officially runs from June 1 through November 30. However, the vast majority of tropical storm and hurricane activity typically occurs during August - October.
Major hurricanes tend to be the deadliest and costliest tropical systems, although disasters also occur due to flooding from less intense hurricanes and tropical storms. Hurricane-spawned disasters occur even in relatively inactive years from land falling systems. For example, in 1992 Hurricane Andrew, the only major hurricane to occur during that relatively inactive year, caused over $30 billion in damage to the United States.The outlook is available on the Internet on the Climate Prediction Center web site at http://nic.fb4.noaa.gov and the Tropical Prediction Center/National Hurricane Center web site at http://www.nhc.noaa.gov