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CSU Team: 2012 Hurricane Season One of the Most Unusual

The 2012 hurricane season was one of the most unusual on record with a significant number of weaker cyclones combined with a general lack of major hurricane activity, according to a report issued Thursday from the Colorado State University hurricane forecast team. Hurricane season ends Friday.

“The 2012 hurricane season had more activity than predicted in our seasonal forecasts. It was notable for having a very large number of weak, high-latitude tropical cyclones but only one major hurricane that lasted for a mere six hours,” said Phil Klotzbach, lead author of the forecast.

The season saw 19 named storms with 10 becoming hurricanes. There was only one major hurricane.

“Superstorm Sandy was a very atypical system that caused some of the most economic damage ever associated with a single storm in U.S. history,” Klotzbach said. “Its destruction was the result of a combination of a mid-latitude cyclone and tropical cyclone whose northwesterly track brought major flooding to the New York City and New Jersey coastal areas.”

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The how-we-did report summarizes tropical cyclone activity in the Atlantic basin during the 2012 hurricane season and compares the team’s forecasts to what actually occurred. The Colorado State team of Klotzbach and William Gray made long-range seasonal forecasts, which called for a slightly below-average hurricane season, on April 4 and June 1. An update issued Aug. 3 called for average activity.

Just as hurricane season began in June, the team forecast 13 named storms, five hurricanes and two major hurricanes with winds over 111 mph. They updated that in August, calling for 14 named storms, six hurricanes and two major hurricanes.

The anticipated El Niño discussed in the seasonal forecasts did not develop as predicted for a number of reasons, Klotzbach said, while anomalous sinking motion at mid-levels in the atmosphere was the primary reason why 2012 was not more active in the tropical Atlantic.

Klotzbach and Gray issued a slew of statistics with their report.

Only 2005 and 1933 had more named storms than the 19 in 2012. In 2005, 28 named storms developed followed by 21 in 1933. They said this was most unusual for a season which only accrued 0.25 major hurricane days and had only one hurricane – Sandy – with a central pressure below 964 millibars.

A total of 10 hurricanes occurred in 2012. Only five other years have had more than 10 hurricanes occur in a single season since 1944.

Additionally the team said that only one major hurricane formed in 2012. This is the least number of major hurricanes to occur in the Atlantic basin since 1997.

No Category 5 hurricanes developed in 2012. This is the fifth consecutive year with no Category 5 hurricanes. The last time that five or more years occurred in a row with no Category 5 hurricanes was 1993 to 1997.

No tropical cyclones reached Category 4 or 5 hurricane strength in 2012. The last time that this occurred was in 2006.

No major hurricanes made landfall on the United States in 2012. The last major hurricane to make U.S. landfall was Wilma in 2005, so the U.S. has now gone seven years without a major hurricane landfall. Since 1878, the U.S. has never had a seven-year period without a major hurricane landfall.

The maximum intensity reached by any tropical cyclone this year was 115 mph with Michael. This is the weakest maximum intensity achieved by the most intense tropical cyclone of a season since 1994 when Florence reached 109 mph.

Beryl became the strongest off-season tropical cyclone on record to make U.S. landfall, when it made landfall on May 28 at 69 mph near Jacksonville, Fla.

Post-tropical Cyclone Sandy, called Superstorm Sandy, generated the lowest pressure ever recorded in the northeast United States at landfall at 943 millibars, breaking the record set by the Great New England Hurricane or Long Island Express in 1938.

The Atlantic has seen a very large increase in major hurricanes during the 18-year period of 1995 to 2012 with an average 3.6 per year in comparison with the prior 25-year period of 1970 to 1994 with its average of 1.5 per year. However, few major hurricanes have made U.S. landfall except for the two very damaging years of 2004 and 2005.

Klotzbach and Gray attribute this upturn in Atlantic major hurricanes to natural multi-decadal variability in the strength of the Atlantic thermohaline circulation and a concomitant increase in tropical Atlantic sea surface temperatures.

Although some scientists have indicated that global warming is a factor in storms such as Sandy, Gray said that although such storms are extremely rare, these types of tropical cyclones are well within natural variability and should not be attributed to increases in human-induced greenhouse gases.

The team bases its annual forecasts on 60 years of historical data and includes factors such as Atlantic sea surface temperatures and sea level pressure and levels of vertical wind shear, which is the change in wind direction with height. They also take into account the impact of an El Niño, which is an unusual warming of waters in the central and eastern tropical Pacific as well as other factors.

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