CONTACT:  Frank Lepore             FOR IMMEDIATE RELEASE:
          Stephanie Kenitzer       11/25/97
 

The El Nino phenomenon influenced hurricane activity in the Atlantic and eastern North Pacific oceans, placing the region's 1997 hurricane season somewhat out of character, according to scientists at the Commerce Department's National Oceanic and Atmospheric Administration.

In the Atlantic, hurricanes were fewer and less in intensity. The eastern Pacific experienced about an average number of hurricanes but had more storms threaten the coastal southwestern United States.

"An Atlantic-eastern Pacific seesaw effect was evident this year," said Gerry Bell of Climate Prediction Center. "El Nino, the abnormal warming of ocean temperatures across the central and eastern Pacific, influenced hurricane activity in both ocean basins."

Jerry Jarrell, acting director of the National Hurricane Center noted that "the Atlantic season, which runs from June 1 to Nov. 30, featured seven tropical storms and three hurricanes. The average is 10 storms and six hurricanes. Only one Atlantic hurricane reached major' strength with sustained wind speeds in excess of 110 mph. The average is two."

Of these seven tropical storms, three developed into hurricanes, Bill, Danny and Erika. Hurricane Danny, which occurred between July 16-26, was the Atlantic season's only land-falling hurricane. Danny's 80-mph winds and about 40-inches of rain caused an estimated $100-million of damage, mostly in Alabama. Only Hurricane Erika, which occurred between Sept. 3-15, was classified as "major," with sustained winds of 125 mph. Fortunately, Erika stayed well out to sea. Hurricane forecasters went the entire month of August with no tropical storm or hurricane activity of any kind in the Atlantic basin. A similar lull last occurred in 1961.

"The eastern Pacific hurricane season was near normal, although some unusual features,were influenced by El Nino," Jarrell notes. "A somewhat expanded region of the east and north Pacific experienced tropical cyclone activity during 1997, as four systems moved into the central Pacific, when one is average."

"Overall, the eastern Pacific season totaled 17 named storms, producing nine hurricanes, with seven classified as major," Jarrell said. Typically, 16 named storms, nine hurricanes and five hurricanes classified as major is considered normal. Hurricane Linda was the most intense hurricane ever measured in the eastern Pacific, with sustained winds of 185 mph. Also, two storm systems affected locations well north of their climatological normal area: Hurricane Ignacio, whose remnants brought record August rains into central California, and Nora, which hit the southern Arizona-California border area as a tropical storm.

El Nino has already affected a large area of the eastern tropical Pacific. More than 9.5-million square miles of the Pacific ocean were as much as 8 degrees Fahrenheit above normal, said Gerry Bell of NOAA's Climate Prediction Center.

"Yearly variability in tropical storm and hurricane activity over both the North Atlantic and eastern North Pacific Ocean basins is strongly related to changes in the vertical wind shear (the variation of winds with altitude)," Bell said. During El Nino years hurricane activity is suppressed across the North Atlantic and occasionally enhanced across the eastern North Pacific. Strong vertical shear typically inhibits tropical storm intensification, while weak vertical shear aids tropical storm development.

Research by Professor William Gray and his colleagues at Colorado State University suggests that one of the consequences of El Nino is a strengthening of westerly winds, which cause increased shear over the low latitudes of the Atlantic basin.

"Yearly variations in hurricane activity have been particularly prominent during the 1990's consistent with the very active El Nino cycle throughout the period," Bell said. "For example, the prolonged Pacific warm episode of 1991-1994 was accompanied by extremely low Atlantic tropical storm and hurricane activity, with only three to four hurricanes observed for four consecutive years. The transition to cold-episodes (La Nina) of 1995 and 1996 contributed to very active Atlantic hurricane seasons and suppressed eastern Pacific seasons in both years, with the 1995 Atlantic season featuring 19 tropical storms, 11 of which reached hurricane status. This count of 19 tropical storms was more than twice that observed in the Atlantic basin during each of the 1991-1994 seasons, averaging six to eight events."

"Scientists generally accept that the changes in vertical wind shear between 1995 and 1997 is linked to the El Nino cycle. However, the full impact and relationship between El Nino and tropical cyclones is still not completely understood," Bell said.

National Hurricane Center's Jarrell summarized the season this way. "Vulnerable coastal populations can't count on more than occasional suppression of Atlantic hurricane activity, given El Nino's limited life. Folks must stay focused and prepared for the one' hurricane -- that Andrew-type storm-- which can occur in any given year, El Nino, or not. Remember, Andrew devastated south Florida in an El Nino year."

NOTE TO EDITORS; For more information on hurricanes, consult the NHC home page at http://www.nhc.noaa.gov

For more information on current "El Nino forecasts and outlooks" and "Special Climate Summaries" which include this year's hurricane activity, check http://nic.fb4.noaa.gov (and click on El Nino)