People urged to prepare as they normally would
The anomalous cooling of ocean waters in the tropical Atlantic Ocean and the warming of sea surface temperatures in the equatorial Pacific Ocean are key factors for an Atlantic Basin hurricane season forecast calling for reduced activity compared with the median during the past 30 years.
Colorado State University scientists Philip Klotzbach and William Gray issued their annual extended range hurricane season forecast Wednesday, calling for 10 named storms, four hurricanes and two major hurricanes this year. The median between 1981 and 2010 is 12 named storms, 6.5 hurricanes and two major hurricanes.
The scientists switched from using a 1950-2000 average as a benchmark this year to the 1981 to 2010 median. Their previous benchmark cited an average of 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes.
Despite the prediction of less activity, the forecasters warned those who are most at risk of being affected by a hurricane not to let down their guard.
Speaking at the National Hurricane Conference in Orlando, Florida last week, Mr. Gray noted that it only takes one hurricane making landfall for it to be an active season for a particular location.
“We want everyone to prepare the same way every year, whether we or anyone else is forecasting an active or inactive year,” he said.
This year, the April report is the only quantitative long range forecast the Colorado State scientists will issue. The duo abandoned issuing a report that predicted exact numbers in early December because the forecast showed no skill, Mr. Klotzbach said.
“If you have a forecast that doesn’t show any skill, it’s probably a good idea to get rid of it,” he said, noting that one of the big problems with a December forecast is that the El Niño/La Niña-Southern Oscillation in the Pacific Ocean – a phenomenon known to have a significant impact on the Atlantic Basin hurricane season – is difficult to predict that far in advance. Mr. Klotzbach said that until there is more skill in forecasting El Niño/La Niña conditions in advance, they were suspending issuing a quantitative forecast in December.
Although forecasting models still have some difficulty in forecasting El Niño/La Niña conditions in early spring, there was a general consensus forming on the topic.
“We’re looking for an El Niño at this point,” he said.
El Niños, which are caused by a cyclical warming of the equatorial Pacific Ocean sea surface temperatures, create more thunderstorms in that part of the world. The outflow from these thunderstorms travels eastward into the Atlantic Basin, creating more variance – or vertical wind shear – between winds in the upper atmosphere and the surface. Wind shear in turn inhibits the formation and strengthening of tropical cyclones.
Chances of land-fall
Part of Mr. Klotzbach and Mr. Gray’s report forecasts the chances of a tropical storm, hurricane or major hurricane hitting particular coastlines.
“We anticipate a below-average probability for major hurricanes making landfall along the United States coastline and in the Caribbean,” the report stated.
The duo calculated the probabilities for at least one major hurricane making landfall along the entire US coastline at 42 per cent, less than the average of 52 per cent for the last century. For the Caribbean, the probability of at least one land-falling major hurricane was put at 34 per cent, down from the average of 42 per cent for the last century.
For the Cayman Islands specifically, the scientists calculated only a 6 per cent chance of a major hurricane tracking within 50 miles this season. The probability for a hurricane of any strength tracking within 50 miles of the Cayman Islands was calculated at 16 per cent. The probability was 28 per cent for a named storm.
Despite the reduced probability of a major hurricane making landfall in the US, Mr. Gray noted last week during the National Hurricane Conference that the US had not had a major hurricane make landfall since Hurricane Wilma in October 2005, even though several of the hurricane seasons since then have been active.
“It’s rare to go that many years without a major hurricane landfall,” he said. “We’ve been lucky, but this can’t keep going on.”
Mr. Klotzbach said that even in a hurricane season with reduced activity, major hurricanes can and have made landfall. He noted that in 1992, Mr. Gray correctly predicted a hurricane season with less activity and only one major hurricane. However, that major hurricane, Hurricane Andrew, made two US landfalls as a major hurricane as was one of the costliest and most destructive hurricanes ever to affect the US.