Coming off of yet another hurricane season that never quite lived up to the forecasts for overly active storm development, weather forecasters at Colorado State University (CSU) late last week predicted that the Gulf of Mexico and other areas surrounding the Atlantic Ocean’s storm breeding grounds can expect a somewhat above-average 2008 hurricane season.
CSU’s first extended-range forecast for 2008 anticipates 13 named storms forming in the Atlantic basin between June 1 and Nov. 30, with seven of the 13 storms predicted to become hurricanes, including three major hurricanes (Category 3 or higher) with sustained winds of at least 111 mph. The forecasters said their analysis was based on a new statistical forecast technique that explains a considerable amount of hurricane variability in hindcasts issued from 1950-2007.
“Despite fairly inactive 2006 and 2007 hurricane seasons, we believe that the Atlantic basin is still in an active hurricane cycle,” said CSU forecaster William Gray. “This active cycle is expected to continue at least for another decade or two. After that, we’re likely to enter a quieter Atlantic major hurricane period like we experienced during the quarter-century periods of 1970-1994 and 1901-1925.”
Oil and natural gas production in the Gulf of Mexico, which was hit hard by hurricanes Katrina and Rita in 2005, was widely spared during the last two years. According to energy consultant IHS, the average annual impact from hurricanes on Gulf production is “relatively modest,” and the impact on supply is “typically short-lived” (see NGI, Oct. 22).
The CSU hurricane forecast team also predicted a 60% chance that at least one major hurricane will make landfall on the U.S. coastline next year. The long-term average probability is 52%. For the U.S. East Coast, including the Florida peninsula, the probability of an intense hurricane making landfall is 37 %; for the Gulf Coast from the Florida panhandle west to Brownsville, in southernmost Texas, the probability is 36%, they said.
The CSU team’s forecasts are based on the premise that global oceanic and atmospheric conditions — such as El Nino, sea surface temperatures and sea level pressure — that preceded active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons. Gray said he expects to see continued fairly warm tropical and north Atlantic sea-surface temperatures, prevalent in most years since 1995, as well as neutral or weak La Nina conditions — “a recipe for enhanced Atlantic basin hurricane activity.” The factors are similar to conditions that occurred during the 1953, 1956, 1989, 1999 and 2000 seasons, which had above-average activity, he said.
The CSU team — like most forecasters — had predicted above average activity during the hurricane season, which closed at the end of November. But the season turned out to be weaker than predicted, with one hurricane, one tropical storm and three tropical depressions hitting the United States — an average season. Tropical Depression Barry came ashore near Tampa Bay, FL, on June 2; Tropical Depression Erin hit southeast Texas on Aug. 16; Tropical Depression Ten came ashore along the western Florida panhandle on Sept. 21; Tropical Storm Gabrielle hit east-central North Carolina on Sept. 9 and Hurricane Humberto hit the upper Texas coast on Sept. 13.
A total of 14 named storms, six hurricanes and two major hurricanes developed in the Atlantic in 2007, a typical season when compared with the 1950-2000 average. The CSU hurricane forecast team had predicted 17 named storms, nine hurricanes and five major hurricanes with their April and June forecasts, lowering their forecast to 15 named storms, eight hurricanes and four major hurricanes in an August update. The team has over-predicted hurricane activity in each of the past two seasons but has been on target in seven of the last nine years, Gray said.
At the beginning of October CSU forecasters said the growing strength of the current La Nina event — the cooling of ocean surface temperatures off the west coast of South America — would cause above-average activity during the final two months of the 2007 Atlantic hurricane season and might extend the season as well (see NGI, Oct. 8).
A variety of factors, including cooler ocean water and wind shear in the central tropical Atlantic, contributed to what turned out to be an average hurricane season, the forecast team said.
“The reasons for this year’s average season are challenging to explain,” said CSU forecaster Phil Klotzbach. “It is impossible to understand how all these processes interact with each other to 100% certainty. Continued research should help us better understand these complicated atmospheric/oceanic interactions.”
Late last month scientists with the National Oceanic and Atmospheric Administration (NOAA) said they were reviewing a set of dynamic weather patterns to understand why there was lower-than-expected hurricane activity in the Atlantic Basin this year (see NGI, Dec. 3). The United States was “largely spared” from significant landfalling storms, but “several noteworthy events took place, including two back-to-back Category 5 hurricanes hitting Central America and the rapid near-shore intensification of the single U.S. landfalling hurricane,” NOAA noted. Like the CSU team, NOAA had forecast above-average hurricane activity at the beginning of the season (see NGI, May 28) before eventually trimming its storm prediction.
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