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CSU Forecast: Plenty of Hurricanes This Year

The U.S. Atlantic basin will likely experience a well above-average hurricane season this year and odds are nearly even that a major hurricane will make landfall on the Gulf Coast, according to weather forecasters at Colorado State University (CSU).

"Current oceanic and atmospheric trends indicate that we will likely have an active Atlantic basin hurricane season," said CSU forecaster William Gray.

The CSU team's forecast calls for 15 named storms forming in the Atlantic basin between June 1 and Nov. 30, with eight of the storms predicted to become hurricanes. Four of those hurricanes are expected to develop into intense or major hurricanes (Category 3 or greater) with sustained winds of 111 mph or greater. Long-term averages are 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.

Conditions in the Atlantic basin are "quite favorable for an active hurricane season," according to the CSU forecasters. The current sea surface temperature (SST) pattern in the Atlantic is typically observed before very active seasons. Warm SSTs are likely to continue in the tropical and North Atlantic during 2008 because of a positive phase of the Atlantic Multidecadal Oscillation, and the current weak Azores High will likely promote weaker-than-normal trade winds over the next few months, enhancing warm SST anomalies in the tropical and subtropical Atlantic, they said. The CSU team also expects neutral or weak La Nina conditions in the tropical Pacific -- cooling ocean surface temperatures off the western coast of South America -- which, combined with a predicted warm North and tropical Atlantic, is a recipe for enhanced Atlantic basin hurricane activity.

These factors are similar to conditions that occurred during the 1950, 1989, 1999 and 2000 seasons, which all had well above-average hurricane activity.

The hurricane forecast team predicts hurricane activity this year will be 160% of the average season. In 2005 hurricane activity was about 275% of the average season, and oil and natural gas production in the Gulf of Mexico were hit hard by Hurricanes Katrina and Rita. Last year 15 named storms, six hurricanes and two intense hurricanes, Dean and Felix, were created during the Atlantic hurricane season. Humberto was a Category 1 hurricane when it hit the west Louisiana area and a series of tropical depressions came ashore at various points, but none caused the kind of damage created by the hurricanes of 2005.

There is a 69% chance that a major hurricane will make landfall on the U.S. coastline in 2008; a 45% chance that a major hurricane will make landfall on the U.S. East Coast, including the Florida Peninsula; and a 44% chance that a major hurricane will make landfall on the Gulf Coast from the Florida Panhandle west to Brownsville, TX. The team also predicted above-average major hurricane landfall risk in the Caribbean.

If current trends in the Atlantic persist, there is a possibility that the forecast could be increased by the time of their first seasonal update in early June, the forecasters said.

A moderate to strong La Nina event occurred during the winter, but it has weakened considerably over the past few weeks, the CSU team said. Fairly strong cold anomalies still exist in the central tropical Pacific, while warm anomalies are now present in the eastern tropical Pacific. "We believe that this La Nina event will likely continue to moderate over the next couple of months," the forecasters said.

The latest forecast from CSU calls for more hurricanes than did its preliminary forecast, released in December, which had predicted a somewhat above-average 2008 hurricane season, with 13 named storms and seven hurricanes, including three major hurricanes (see NGI, Dec. 10, 2007).

The CSU hurricane team's prediction is in line with one made in January by WSI Corp. forecasters, who 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 La Nina event would bring an active 2008 Atlantic hurricane season (see NGI, Jan. 7). WSI's forecast called for 14 named storms and seven hurricanes, including three intense hurricanes, during the coming Atlantic hurricane season.

The CSU and WSI forecasts are at odds with findings by climate scientists at the National Oceanic and Atmospheric Administration (NOAA), who have said warmer ocean waters could mean fewer Atlantic hurricanes striking the United States this year (see NGI, Jan. 28). In a report published in Geophysical Research Letters, the NOAA scientists said warming of global SSTs is associated with a sustained long-term increase of vertical wind shear in the main development region for Atlantic hurricanes.

The CSU hurricane team's forecasts are based on the premise that global oceanic and atmospheric conditions -- such as El Nino, SSTs and sea level pressures -- that preceded active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons.

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