Colorado State Team Reduces Their 2002 Hurricane Season Forecast, Issues New Monthly Storm Predicitions for August and September

Note to Editors: Forecast totals are in the attached chart. The complete hurricane forecast including the new August and September monthly forecasts, a detailed description of forecast factors, press releases, and access to downloadable audio and video clips are available on the World Wide Web at www.colostate.edu or at http://typhoon.atmos.colostate.edu. A new follow-up September forecast and seasonal update will be issued on Sep. 2.

Although the past few weeks have witnessed two Atlantic basin tropical storms (Arthur and Bertha), overall ocean and atmospheric fluctuations since the June 1 start of the 2002 hurricane season have convinced William Gray and the Colorado State University hurricane forecast team that this year will not be nearly as active as they had anticipated in earlier forecasts.

"The fact that we have witnessed two weak early season high latitude named storms does not mean we will have an active hurricane season," said Gray. "In fact, due to recent changes in climate signals, we now believe the 2002 Atlantic basic hurricane season will be considerably below the long term average and much below what has been experienced in six of the last seven years. The primary decrease is expected to occur in the most intense storms and in the frequency of low latitude storms."

Today’s forecast reduces the May 31 prediction of 11 named storms, six hurricanes and two major hurricanes to nine named storms, four hurricanes and only one major hurricane. The long-term average is 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes per year.

"We have rarely witnessed the rapid and simultaneous types of Atlantic basin hurricane inhibiting conditions that have taken place between April and July of this year," said Gray. "The inhibiting changes include a cooling of Atlantic basin sea surface temperatures, a large increase in Atlantic sea surface pressures, and a strengthening of tropical Atlantic easterly trade winds and upper level tropospheric westerly winds."

According to Gray, each of these factors can reduce Atlantic hurricane activity. The forecast team additionally credits a strengthening El Nino in the equatorial Pacific to be another inhibiting factor to this season’s Atlantic storm activity.

"This year’s El Nino does not play nearly as important a role as the extremely strong El Nino event of 1997, the last year the United States witnessed a below average hurricane season," said Gray. "This year, it is the Atlantic basin which is experiencing the major hurricane inhibiting conditions."

As part of today’s updated report, the Colorado State team reduced their assessment of hurricane landfall probability. For the first time in five years, landfall probabilities are predicted to be below the long-term average.

"This is good news for coastal residents. However, this does not mean that there will not be significant United States and Caribbean hurricane spawned destruction," said Gray. "For example, 1992’s Hurricane Andrew was the only major storm in a very inactive year but came ashore in south Florida and Louisiana and caused extensive damage."

The Colorado State team forecasts a 49 percent probability of one or more major hurricanes hitting somewhere along the United States coastline in 2002 (the last century’s average probability was 52 percent). For the U.S. East Coast and Florida Peninsula, the probability of one or more major hurricanes making landfall this year is 28 percent. For the U.S. Gulf of Mexico, the probability is 29 percent.

The last seven years have witnessed 94 named storms, 58 hurricanes and 27 major hurricanes in the Atlantic basin. During that period, only three of the 27 (or one in nine) Atlantic basin major hurricanes (Opal, Bret and Fran) crossed the U.S. coastline. Based on historical averages, one in every three major hurricanes come ashore in the United States.

"We have been very fortunate over the past seven years in having only three major hurricanes make landfall in the United States, but we cannot expect this luck to continue indefinitely," said Gray. "Even in below-average storm seasons such as this one is expected to be, people living along the southeastern U.S. coastline and in the Caribbean basin must remain alert and prepared."

A new aspect to the team’s research is the issuing of storm activity forecasts for specific months. Along with today’s seasonal forecast, Gray and his colleagues issued individual monthly forecasts for August and September. The monthly forecasts use different parameters than the seasonal forecasts to predict storm activity within shorter time periods. The individual monthly forecasts aid with the seasonal predictions and can be found included in the updated forecast report on the research team’s Web site at http://typhoon.atmos.colostate.edu.

"The same factors that can make August an active or inactive storm month are often not the same factors that can make the entire season active or inactive," said Gray. "We hope to continue to improve our forecasts to provide people with specific monthly hurricane forecasts and specific landfall probability forecasts throughout future seasons."

Also new this year, the research team will issue a follow-up September forecast and seasonal update on Sep. 2.

The storm seasons spanning 1995-2001 comprised the most active seven consecutive hurricane years on record and the Colorado State forecasting team believes that we are in a new multi-decadal era for increased storm activity such as occurred in the 1940s and 1950s. They add that in this new era, as in the past, there will be individual years with below-average numbers of hurricanes. This year is expected to be one of these temporary deviations from the long-period average.

The Colorado State forecast team does not attribute changes in recent and projected Atlantic hurricane activity to human-induced global warming or any other human-caused phenomenon. They believe the changes are a natural consequence of climate variability that has been a continuing feature of atmosphere-ocean changes since the last Ice Age.

Gray, in his 19th year of forecasting Atlantic basin storms, believes that recent improvements in the gathering, archival and data analysis techniques of global atmospheric and oceanic signals can be used to improve forecasts of Atlantic basin hurricane activity and landfall probability. He and his team search for global atmospheric and oceanic parameters which have provided information that distinguishes between past active vs. inactive hurricane seasons at various time lags. They assume that past atmosphere-ocean lag relationships that have occurred in the past will also occur in the future. Team members other than Gray include Chris Landsea, Eric Blake, Philip Klotzbach and John Sheaffer.

GRAY RESEARCH TEAM
ATLANTIC BASIN HURRICANE FORECAST FOR THE 2002 SEASON

Tropical Cyclone Parametersand 1950-2000 Climatology(in parentheses)	7 Dec. Forecastfor 2002	5 April 2002 Forecast	31 May 2002 Forecast	Updated 7 August Forecast
Named Storms (9.6)*	13	12	11	9
Named Storm Days (49.1)	70	65	55	35
Hurricanes (5.9)	8	7	6	4
Hurricane Days (24.5)	35	30	25	12
Intense Hurricanes (2.3)	4	3	2	1
Intense Hurricane Days (5.0)	7	6	5	2
Net Tropical Cyclone Activity (100%)	140	125	100	65

* Number in ( ) represents average year totals based on 1950-2000 data.