LSU climatologists use historical records to put 2005 season in perspective
On Tuesday, Aug. 2, the National Oceanographic and Atmospheric Administration revised its previous hurricane forecast, predicting that there would be an additional 11-14 named storms in 2005. This brought the total projection for the year to 18-21 storms. Based on their research into hurricane season records dating back to 1851, two LSU climatologists believe that this new prediction is likely accurate and that 2005 could rival some of the busiest seasons ever recorded.
Kevin Robbins, associate professor of geography & anthropology at LSU and director of the Southern Regional Climate Center, and LSU Assistant Professor of Geography & Anthropology and State Climatologist Barry Keim, examined hurricane season records from 1851-2005. They concentrated on the top 10 seasons with the earliest occurrences of named storms: 1887, 1893, 1933, 1936, 1990, 1995, 1996, 2003, 2004 and 2005.
Robbins and Keim discovered that, in terms of the number of named storms, these seasons were more active than average. The average is 9.6 named storms per season, however, these "early start" seasons averaged 16.1 named storms over the complete season.
The 2005 season is off to a record start. As of Aug. 3, NOAA had observed and named eight tropical storms, of which two became Category 4 hurricanes with winds of at least 131 miles per hour. Based on the records going back to 1851, this season set records for the earliest occurrence of the fourth, fifth, sixth, seventh and eighth named storms. According to the historical record, 1936 set the record for the earliest occurrence of nine named storms. If another named storm occurs before Aug. 20, then 2005 will break this record as well.
"We are still very early in the hurricane season, which usually shows peak activity from mid-August through early October," said Robbins. "Storms during this period are usually more frequent, of longer duration and of higher intensity due to atmospheric and oceanic conditions that are favorable to storm development."
Robbins and Keim said that the likelihood of tropical storm and hurricane development is increased by warm sea surface temperature, known as "SST," and low wind shear in formation regions. According to their research, the period from the mid-1920s to the mid-1960s had warmer-than-normal SST and exhibited "very active hurricane seasons." This was followed by a period of cooler SST and relative calm that lasted until 1994. This changed again in 1995, which began a period of higher SST and heightened hurricane activity that is ongoing and likely to continue for several decades.
Keim's and Robbins' research also revealed another active period of storms from roughly 1870 to 1910, with some extremely active years evident in the late 1880s and early 1890s.
"We entered into a heightened period of Atlantic tropical activity, beginning in 1995 that is expected to be multi-decadal. Elevated SST in the tropical Atlantic, favorable upper air conditions in key storm formation regions and comparison to other years with early season activity all point to a very intense hurricane season for 2005," said Keim. "While no two seasons are totally alike, the 2005 hurricane season could rival historically significant years such as 1887, which had 19 named storms; 1933, which had 21 named storms; and 1995, which had 19 named storms."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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