Note to Editors: The following information was gathered in a May 25 interview with Colorado State University hurricane forecaster William Gray. Tape is being supplied to ABC, CBS, CNN, Fox and NBC May 27 (please check with your network for availability), and an audio feed will be available at approximately 8 a.m. MDT May 27 at (970) 491-1525. Gray’s regularly scheduled June update on the hurricane season forecast will be placed on the Web June 4 at http://tropical.atmos.colostate.edu/forecasts.
As the official June 1 start of the 1999 hurricane season approaches, Colorado State University hurricane forecaster William Gray foresees "a very active season."
Gray and his colleagues, whose most recent updated forecast in early April called for 14 tropical storms, 10 hurricanes and four intense hurricanes during the official June 1-Nov. 30 season, anticipate little change at this point.
"The odds favor an active year because the climate signals that we’ve seen out there are similar to the precursor climate signals of rather active years" in the past, Gray said. The April numbers compare with last year’s actual total of 14 tropical storms, 10 hurricanes and three intense hurricanes and with long-term (1950-1990) averages of 9.3 tropical storms, 5.8 hurricanes and 2.2 intense hurricanes annually.
What argues for another active season, Gray said, are a number of climate signals that favor the development of hurricanes. They include:
- The persistence of La Niña, an upwelling of cold water in the eastern equatorial Pacific.
- Stratospheric westerly winds.
- North Atlantic water temperatures on the warm side and generally higher sea-surface temperatures for the entire Atlantic.
- Existing and projected sea-surface barometric pressures for the Caribbean Basin and western Atlantic somewhat below average.
"An important factor with all this, I think, is that we believe we’ve entered this new era for storm activity," Gray said. "There was a big change in the climate signals between 1994 and 1995, when the North Atlantic temperatures changed a lot and climate signals began to alter, not just in the Atlantic but around the globe.
"We think these changes are normal, natural changes that are not due to anything humankind has imposed, such as a warming effect from greenhouse gases."
Gray warns that the four projected intense hurricanes, with wind speeds of 111 mph or higher, pose a particular threat should they approach land, since Gray’s calculations, based on other studies, have indicated that intense (Saffir-Simpson category 3-5) hurricanes make up only 25 percent of all storms but cause some 85 percent of all damage.
"The problem with that is that we’ve had such an increase in property and population along the southeast U.S. coast and the Florida peninsula," he said. The past quarter century (1970-1994) has been relatively quiescent. While exceptions such as Andrew in 1992 and Mitch last year caused massive damage, U.S. coastal areas generally haven’t experienced the cycle of intense, landfalling storms that lashed the East Coast from the late 1920s through the late 1960s.
Gray is now in his 16th year of forecasting the number of hurricanes in the Atlantic Basin (the North Atlantic, Caribbean Sea and Gulf of Mexico). Ten of his forecasts have been on or close to the actual numbers for the season and five others have been less accurate but have beaten the long-term averages. The forecasts predict only numbers, not dates, points of origin or ensuing tracks.
After studying the influence of El Niño and later La Niña on his forecasts since the early 1970s, Gray warned against oversimplifying the impact of these phenomena despite La Niña’s presence this year.
"A lot of people feel El Niño-La Niña is the factor that causes hurricane activity to go up or down, but it’s only one among many," he said. "Stratospheric winds, West African rains, Atlantic sea-surface temperatures, Atlantic barometric pressures and other factors around the globe also affect hurricanes.
"Given the precursor climate and oceanic signals we have now, it’s hard to see how this could be an inactive year."