A Cooler Atlantic Leads Colorado State’s Forecast Team to Lower Hurricane Prediction and Call for an Average Storm Season

Note to Editors: Forecast totals are in the attached chart. The complete hurricane forecast, a detailed description of forecast factors, press releases and downloadable audio clips are available on the World Wide Web at www.colostate.edu or at http://typhoon.atmos.colostate.edu.

Cooler than expected April and May Atlantic sea surface temperatures have led atmospheric scientist William Gray and his Colorado State University hurricane forecasting team to decrease their Atlantic basin hurricane forecast numbers. However, Gray and his colleagues still predict an average Atlantic 2002 hurricane storm season.

"We still anticipate this year’s hurricane season to be reasonably active," Gray said. "We lowered our April forecast by one named storm, one hurricane and one major hurricane primarily because Atlantic surface temperatures have become cooler than expected over the past few months. We foresee activity to be typical of the average hurricane seasons between 1950-2001, but the probability of United States hurricane landfall will be above average."

In a report released today (May 31), Gray and his colleagues updated their predictions for the 2002 season, which extends from June 1-Nov. 30, and call for 11 named storms, six hurricanes and two major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater. Today’s forecast reduces early April’s predictions of 12 named storms, seven hurricanes and three major hurricanes. The average per year is 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes.

Gray and his team believe the weak El Nino event in the eastern equatorial Pacific is another inhibiting factor to this season’s Atlantic storm activity. However, this year’s El Nino is not expected to play as dominant a role in weakening Atlantic storm activity as occurred in the greatly reduced hurricane seasons of 1997, 1986-87 and 1982-83.

As part of today’s updated report, the Colorado State team also reduced their assessments of the probabilities of hurricanes making landfall in the United States. Gray warns that landfall probabilities still remain higher than the long-term average due to the current multi-decadal era for more active hurricane activity that began in 1995.

The Colorado State team forecasts a 63 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 42 percent. For the U.S. Gulf of Mexico, the probability is 35 percent.

"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," said Gray. "With the exploding growth in coastal populations, people living on the southeastern U.S. coastline, especially along the southern half of the Florida Peninsula, must be prepared in the next few decades for landfalling hurricanes and levels of destruction many, many times greater than anything that has been witnessed in the past 35 years."

The storm seasons spanning 1995-2001 comprised the most active seven consecutive hurricane years on record, with the Atlantic basin witnessing 94 named storms, 58 hurricanes and 27 major hurricanes. During that period, only three of the 27 Atlantic basin major hurricanes (Opal, Bret and Fran) crossed the U.S. coastline. Based on historical averages (which show that one in every three major hurricanes come ashore in the United States), Gray said that the United States should have experienced eight or nine major hurricane landfall events since 1995 but did not because of a combination of an upper-level air trough off of the East Coast and just plain luck.

The United States has observed 19 consecutive Atlantic basin hurricanes within the last two-and-a-half years without one crossing the U.S. coastline, a record for consecutive Atlantic basin hurricanes not making landfall. Additionally, over the past three-and-a-half decades, the United States has seen an overall decrease in major hurricane landfalls. According to Gray, this has been due to a rare combination of multi-decadal global ocean circulation changes, but this downward cycle cannot be expected to continue.

"The storms have been out there, but they have just not come ashore," said Gray. "Climatological averages will eventually correct themselves, and when that happens, we will see a significant increase in the number of major hurricanes making landfall in the United States."

Major hurricanes make up about a quarter of all named storms, but when accounting for population, inflation and wealth per capita, those storms cause approximately 85 percent of all tropical cyclone-spawned destruction.

Gray and his team do not attribute recent and projected Atlantic hurricane increases to human-induced global warming. 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 and his research colleagues employed a new forecast strategy this year that places increased emphasis on circulation features of the middle latitudes while removing previously relied-upon African rainfall information. The new strategy uses Quasi-Biennial Oscillation (QBO, the equatorial east-west stratospheric winds that vary with a period of 26-30 months), a measure of Atlantic sea surface temperature, sea-surface pressure anomalies, a prediction of El Nino conditions, and other global atmospheric and oceanic signals.

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, including Chris Landsea, John Sheaffer and Phil Klotzbach, search for global atmospheric and oceanic parameters which in the past have provided information that distinguishes between active vs. inactive hurricane seasons at various time lags. Based on this data, the team makes an assumption that the atmosphere in the future will behave like it has in the past.

Gray and his research team issue seasonal Atlantic basin hurricane forecasts annually in early December, early April, late May and early August. Their next and last seasonal update will be issued on Aug. 7 just before the start of the most active portion of the hurricane season. The team also will issue separate individual monthly forecasts for August and September with the August seasonal update.


Tropical Cyclone Parameters and 1950-2000 Climatology (in parentheses) 7 Dec. Forecast for 2002 5 April 2002 Forecast Updated May 31 Forecast
Named Storms (9.6)* 13 12 11
Named Storm Days (49.1) 70 65 55
Hurricanes (5.9) 8 7 6
Hurricane Days (24.5) 35 30 25
Intense Hurricanes (2.3) 4 3 2
Intense Hurricane Days (5.0) 7 6 5
Hurricane Destruction Potential (72.7)** 90 85 75
Net Tropical Cyclone Activity (100%) 140 125 100

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

** Hurricane Destruction Potential measures a hurricane’s potential for wind and ocean surge damage. Tropical Storm, Hurricane and Intense Hurricane Days are four six hour-long periods where storms attain wind speeds appropriate to their category on the Saffir/Simpson scale.