Weather related stories were big news in 2007, with heat and drought scorching the South and Southeast, wildfires burning their way through southern California and global warming worries worldwide, but perhaps the biggest weather story of the year was the Atlantic hurricane season that wasn't.
Colorado State University weather forecaster William Gray told NGI that storm activity during the 2007 hurricane season, which included 15 named storms, was about 95% of the average year. "But we only had six hurricanes, and some of those were very short-lived and were not that strong," Gray said. "As we characterize the season, we had these two very intense storms, Dean and Felix, that were Category 5s, and we say we had two major, intense storms and 13 pieces of junk. We all thought that we'd have more storms than we did. We didn't have those long-lasting storms, those storms in the tropics that are on the map for 10 days or so."
"But what made this season seem so inactive is that we had so few landfalls...we only had a very minor one, Humberto, that hit in the west Louisiana area as a Category 1, so people said 'it was a huge bust.' In terms of landfalling storms it was a bust, yes, but in terms of numbers it wasn't quite as inactive as many seasons in the past."
In addition to Humberto, 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; and Tropical Storm Gabrielle hit east-central North Carolina on Sept. 9. The final named storm of the season, hurricane Olga, formed from the interaction of a cold front and a small area of disturbed weather in the north Atlantic in late November and roamed across the ocean for several days before dissipating east of the Bahamas Dec. 5.
Most forecasters initially predicted conditions would be right to produce more than the usual number of hurricanes but, as the season went on and few storms made landfall, lower revised numbers were released. 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.
In late November 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 (see NGI, Dec. 3, 2007). 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, 2007) before eventually trimming its storm prediction.
Looking at data going back nearly a century, Gray said 2007's season-long La Nina event -- the cooling of ocean surface temperatures off the west coast of South America -- has historically been a recipe for hurricane production. But in October an unexpected stationary trough -- an upper air low pressure system -- off the east coast and a half degree centigrade cooling of water temperatures off the West coast of Africa blunted La Nina's effects.
"Those were the two things that we really just hadn't expected to happen, and I think explains why instead of having a season at about 150% of the previous year we only had about 100% overall," Gray said.
Looking ahead, Gray and his CSU forecasting team have 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 (see NGI, Dec. 10, 2007). CSU's first extended-range forecast for 2008 anticipated 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 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 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."
Similarly, WSI Corp. forecasters last week said a continuation of warmer-than-normal Atlantic Ocean temperature anomalies into the summer and fall and the likelihood of a favorable or neutral wind shear environment on the heels of the current La Nina event will bring an active 2008 Atlantic hurricane season (see related story). WSI's forecast called for 14 named storms and seven hurricanes, including three intense hurricanes (Category 3 or greater) during the coming Atlantic hurricane season. The forecast numbers are all larger than the 1950-2007 averages of 9.7 named storms, 5.9 hurricanes and 2.3 intense hurricanes. Hurricane season runs from June 1 to Nov. 30.
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 an October report from 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, 2007).
Some forecasters say global warming could produce more strong storms, and 2007 was one of the 10 warmest years the contiguous United States has experienced since national records began in 1895, according to preliminary data from NOAA's National Climatic Data Center (see NGI, Dec. 17, 2007). The global surface temperature for 2007 is expected to be the fifth warmest since worldwide records began in 1880, NOAA said.
When all data is evaluated later this month, the average temperature for 2007 across the United States is expected to be near 54.3 degrees Fahrenheit, 1.5 degrees above the 20th century mean of 52.8 degrees and the eighth warmest year on record, NOAA said. Only one March and one August in the last 113 years were warmer than those months were in 2007, and only two months this year -- February and April -- were cooler-than-average. During a severe heat wave across much of the central and southeastern U.S. more than 2,500 new daily record high temperatures were recorded.
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