Active 2013 hurricane season foreseen
The strange weather of 2012 continued when the Cayman Islands National Weather Service recorded a monthly record low rainfall accumulation of 0.58 inches for the month of November.
Chief Meteorologist John Tibbetts said the total was some 5.47 inches below the normal rainfall total of 6.05 inches.
“This total represents the second straight year where a new record low rainfall amount [for November] was recorded and the third straight year in which the November rainfall total was significantly below normal,” Mr. Tibbetts said.
November became the third month of the year in Grand Cayman in which a new record for either the most or the least rainfall occurred. New records for the most rainfall in a particular month were set in both April and May. In April, 7.4 inches of rain fell, much more than the monthly 30-year average of 1.27 inches and more than the previous record of 6.41 inches that fell in 1985.
In May, 17.72 inches of rain fell during the month, including 8.5 inches on the morning of 21 May. This amount was not only much higher than the average of 5.96 inches of rain for the month, it broke the previous record of 16.14 inches set in 2002.
But after the exceptionally wet spring, June and July received less than half the average rainfall, August then received considerably more than average before September, October and November all received less than the 30-year average.
Despite the very dry autumn, Mr. Tibbetts said the National Weather Service has recorded 58.76 inches of rain through the end of November, already 2.56 inches above Grand Cayman’s average annual rainfall of 56.18 inches. Another 1.55 inches of rain – unconfirmed – had already fallen over the first nine days of December, meaning Grand Cayman will top 60 inches of rain for the year. However, that is far short of the record of 84.5 inches that fell in 1979.
Strange rainfall patterns in Grand Cayman occurred during the same year as a hurricane season that had what has been called “highly anomalous tropical cyclone activity” by Colorado State University scientists William Gray and Phil Klotzbach. Even though there were 19 named storms this year – tied for the third most in recorded history – only one became a major hurricane and most were weak, high latitude cyclones.
Although Mr. Gray and Mr. Klotzbach no longer make quantitative extended-range hurricane season forecasts in December for the following year, the duo issued a qualitative discussion about the 2013 hurricane season last Friday.
“One of the big uncertainties for the 2013 Atlantic basin hurricane season is whether or not El Niño will develop,” the scientists wrote, later noting that several forecasting models, and one key model in particular, are showing the onset of an El Niño, a cyclical warming of sea surface temperatures in the equatorial Pacific Ocean. When El Niño events occur, they are known to produce higher wind shear in the Atlantic basin, which inhibits the formation and strengthening of tropical cyclones.
Based on several variable criteria, Mr. Klotzbach and Mr. Gray see at this point a 20 per cent chance of a very active hurricane season; a 40 per cent chance of a slightly more active than normal season; a 35 per cent chance of normally active hurricane season; and a 5 per cent chance of a hurricane season with less than normal activity.
United Kingdom-based Tropical Storm Risk issued its extended-range forecast for the 2013 Atlantic Hurricane Season last week as well, predicting more tropical cyclone activity than normal with 15.4 storms, 7.7 hurricanes and 3.4 major hurricanes, all higher than the 63-year norm of 10.8 named storms, 6.3 hurricanes and 2.7 major hurricanes with sustained wind speeds of 111 miles per hour or above.
“There is a 59 per cent probability that the 2013 Atlantic hurricane … will be above average … a 27 per cent likelihood it will be near normal … and a 14 per cent chance it will be below normal …” the forecast report stated.