The Colorado State University team of Phil Klotzbach and William Gray on Friday continued to predict an above-average 2013 Atlantic basin hurricane season, although the forecast numbers have been reduced slightly due to some anomalous cooling in the eastern tropical and subtropical Atlantic.
“While the tropical Atlantic remains warmer than normal, it has cooled somewhat in the eastern portion of the basin,” Klotzbach said. “However,” he continued, “it appears that the chances of an El Niño event this summer and fall are unlikely.”
“Typically El Niño is associated with stronger vertical shear across the tropical Atlantic, creating conditions less conducive for storm formation.”
The team calls for 18 named storms during the hurricane season that runs June 1 to Nov. 30. Eight of those are expected to become hurricanes and three of those are expected to become major hurricanes with sustained winds of 111 mph or greater. This is a slight reduction from the early April and early June forecasts when the team called for 18 named storms, nine hurricanes and four major hurricanes.
So far, four named storms have formed in the Atlantic basin but none have intensified into hurricanes.
For the next week, the layer of Sahara dust currently in the area will keep storm formation at bay, meteorologist Luis Rosa at the National Weather Service in San Juan said Friday.
“The very dry, very stable environment will suppress thunderstorm formation,” he said.
Rosa said the Saharan air mass is pretty warm and will likely cause some record high temperatures on Saturday.
According to Rosa, the territory won’t have any chance of rain till Wednesday when another tropical wave arrives. He said it would then dry out again through the weekend that begins Aug. 9.
However, he and Gray urged residents to remain vigilant because the most active part of hurricane season is still a couple of weeks away. Rosa said the busiest time for hurricanes is Aug. 20 through Sept. 15.
“All vulnerable coastal residents should make the same hurricane preparations every year, regardless of how active or inactive the seasonal forecast is,” Gray said. “It takes only one landfall event near you to make this an active season.”
The Colorado State team’s probabilities for a major hurricane making landfall on U.S. soil during the remainder of the hurricane season stand at 53 percent for the entire Caribbean. The average for last century is 42 percent.
The team predicts that tropical cyclone activity in 2013 will be about 150 percent of the average season. By comparison, 2012 witnessed tropical cyclone activity that was 131 percent of the average season.
According to Gray and Klotzbach’s press release, four hurricane seasons since 1950 exhibited oceanic and atmospheric characteristics most similar to those observed in June-July 2013 and expected during this year’s hurricane season: 1952, 1996, 2007, and 2008. The activity over these four years was above average.
The forecasts are based on the premise that global oceanic and atmospheric conditions – such as El Niño, Atlantic basin sea surface temperatures and sea level pressures – that preceded active or inactive hurricane seasons in the past provide meaningful information about similar conditions that will likely occur in the current year.
The team does not give credence to the hypothesis that rises in carbon dioxide may have a significant impact on this year’s hurricane activity.
Colorado State is in its 30th year of issuing Atlantic basin seasonal hurricane forecasts. The team’s annual predictions are intended to provide a best estimate of activity to be experienced during the upcoming season, not an exact measure.
The Atlantic basin has been in an active period for hurricane activity since 1995, due to an active phase of the Atlantic Multi-Decadal Oscillation, which fluctuates on a 25- to 35-year timescale.
Other than the very active landfall years of 2004 and 2005, the United States has not experienced as many landfalling major hurricanes as would be expected given this active cycle. There has never been a period in the historical record dating back to 1851 where seven years have passed without a major hurricane making landfall. These fortunate conditions should not be expected to continue.