Colorado State’s Hurricane Update Reduces Storm Activity but Forecast Still Calls for Above-Average Hurricane Season

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In a report released today, Colorado State University’s hurricane forecasting team, led by atmospheric scientist William Gray, decreased its 2002 hurricane activity forecast numbers from their early December estimates but still predicts an above-average Atlantic basin hurricane season. Gray announced the updated forecast this morning at the National Hurricane Conference in Orlando, Fla.

"The upcoming June 1-Nov. 30 hurricane season continues to look like an above-average one," Gray said. "Although we have adjusted our forecast numbers down by one cyclone due to the development of a stronger El Niño than we anticipated in December, we still foresee an active 2002 hurricane season."

Gray and his colleagues’ updated predictions for 2002 call for 12 named storms, seven hurricanes and three major hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater. The average per year is 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes. Major hurricanes account for about a quarter of all named storms, but when normalized for population, inflation and wealth per capita, those storms cause about 85 percent of all tropical cyclone-spawned destruction.

The research team does not expect the currently forming El Niño to be strong enough to greatly reduce this year’s hurricane activity such as occurred in 1997, 1987, 1983 and 1972. Gray and his colleagues foresee hurricane activity in 2002 to be more typical of the seasons of 1951, 1953, 1957 and 1969 which had moderate El Niños and warm Atlantic sea surface temperatures similar to what is expected this year.

"A remarkable upturn in Atlantic Basin hurricane activity has occurred the past seven years," Gray said. "We believe we have entered a new, multi-decadal era for increased storm activity, particularly an increase in the number of major hurricanes, which will likely last another two or three decades."

Gray and his team also forecast an increase in United States hurricane landfall probability. The team predicts a 75 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 57 percent. For the U.S. Gulf of Mexico, the probability is 43 percent.

The recent period from 1995-2001 has constituted the most active seven consecutive years on record, with the Atlantic basin witnessing 94 named storms, 58 hurricanes and 27 major hurricanes. However, Gray pointed out that only three of the 27 major hurricanes (Opal, Bret and Fran) crossed the United States coastline. Over the last century, approximately one in every three major hurricanes made landfall in the United States.

According to the Colorado State research team, this nation should have experienced about nine major hurricane landfall events since 1995. Additionally, the United States has witnessed 19 consecutive Atlantic basin hurricanes within the last two-and-a-half years without one of the hurricanes making landfall.

"This has never happened before. We have been very lucky," Gray said. "The storms have been out there, but they have just not come ashore. By contrast, the Caribbean basin has seen a great increase in landfalling hurricanes since 1995."

Beyond the past seven years, the United States also has seen a significant decrease in major hurricane landfalls over the past three-and-a-half decades. According to Gray, this pattern has resulted from a rare combination of multi-decadal global circulation changes and pure luck and cannot be expected to continue.

"We should anticipate the century-long landfall climatology to eventually right itself and must expect a large increase in landfalling hurricanes in the coming years," Gray said. "With exploding growth in coastal populations and property values, we must be prepared for levels of hurricane damage many, many times greater than has occurred in the past three decades."

The team does 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 that has not been a skillful forecast tool in recent years. The new forecast scheme continues using quasi-biennial oscillation (the equatorial east-west stratospheric winds that vary with a period of 26-30 months), a measure of Atlantic sea surface temperature and sea-surface pressure anomalies, a prediction of El Niño conditions for 2002, and other global atmospheric and oceanic signals.

Now in his 19th year of forecasting Atlantic basin storms, Gray, along with colleagues Christopher Landsea, Eric Blake and Philip Klotzbach, continues to demonstrate that many global atmospheric and oceanic precursor signals can be used to estimate future Atlantic basin hurricane activity and landfall probability. The team searches for global atmospheric and oceanic parameters which, in the past, have shown the ability to distinguish between active vs. inactive hurricane seasons at various time lags, then applies this analysis to predict future year conditions.

Although the team consistently is improving its hurricane prediction skill, they believe there are yet more skillful precursor signals to be found by means of an empirical approach. Gray and his colleagues concede that their forecasts can fail in some years, but when applied over a period of several years, those forecasts show that the atmosphere and oceans have a long and reliable memory for future events.

Gray and his team will be issuing 2002 season update forecasts again on May 31 (to coincide with the official start of the hurricane season on June 1) and August 7. These later, updated forecasts should be more reliable, Gray said. The team also will be issuing separate monthly forecasts for August and September with their early August forecast.


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

* 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.