2015 Atlantic hurricane season still well-below average

Colorado State University researchers continue to predict a well below-average hurricane season for the Atlantic basin in 2015, citing the development of a strong El Niño event as well as continued unfavorable hurricane formation conditions in the tropical Atlantic.

The CSU Tropical Meteorology Project team is calling for eight named storms during the Atlantic hurricane season, which officially runs from June 1 to Nov. 30. The eight named storms that are predicted include Ana, Bill and Claudette, which have already formed. Of those eight named storms, researchers expect two to become hurricanes and one to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 miles per hour or greater.

The team bases its forecasts on over 60 years of historical data that include Atlantic sea surface temperatures, sea level pressures, vertical wind shear (the change in wind direction and speed with height in the atmosphere), El Niño (warming of waters in the central and eastern tropical Pacific), and other factors.

Other quiet years

So far, the 2015 season is exhibiting characteristics similar to the 1965, 1972, 1982, 1987 and 1997 hurricane seasons, all of which had below-normal activity, said Phil Klotzbach, lead author of the report.

“The tropical Atlantic continues to exhibit conditions that are less conducive for tropical cyclone formation, and a strong El Niño event has already developed,” Klotzbach said. “Historical data indicate fewer storms form in these conditions.” Caribbean vertical shear is at record high levels through the end of July (based on a dataset that starts in 1979).

The team predicts that 2015 tropical cyclone activity will be about 40 percent of the average season. By comparison, 2014’s tropical cyclone activity was about 75 percent of the average season.

The CSU team will issue two-week forecasts beginning Aug. 4 and continuing every other Tuesday through the remainder of the peak of the Atlantic hurricane season.

This is the 32nd year that CSU researchers have issued the Atlantic basin season hurricane forecast. William Gray launched the report in 1984. The CSU forecast is intended to provide a best estimate of activity to be experienced during the upcoming season, not an exact measure.

Probability of landfall

Klotzbach cautioned coastal residents to take the proper precautions, regardless of the below-average basin-wide forecast. Inactive Atlantic hurricane seasons can still have major US hurricane damage, with three relatively recent notable examples being 1965 (Hurricane Betsy), 1983 (Hurricane Alicia) and 1992 (Hurricane Andrew).

“It takes only one landfall event near you to make this an active season,” he said.

The report also includes the post-31 July probability of major hurricanes making landfall on U.S. soil:

  • 23 percent for the entire U.S. coastline (full-season average for the last century is 52 percent)
  • 12 percent for the U.S. East Coast including the Florida peninsula (full-season average for the last century is 31 percent)
  • 12 percent for the Gulf Coast from the Florida panhandle westward to Brownsville (full-season average for the last century is 30 percent)
  • 12 percent for the Caribbean (full-season average for the last century is 42 percent)

The forecast team also tracks the likelihood of tropical storm-force, hurricane-force and major hurricane-force winds occurring at specific locations along the coastal United States, the Caribbean and Central America through its Landfall Probability website.

The site provides information for all coastal states as well as 11 regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. Landfall probabilities for regions and counties are adjusted based on the current climate and its projected effects on the upcoming hurricane season.

Klotzbach and Gray update the site regularly with assistance from the GeoGraphics Laboratory at Bridgewater State University in Massachusetts. Funding for this year’s report has been provided by Interstate Restoration, Ironshore Insurance, Macquarie Group and a grant from the G. Unger Vetlesen Foundation.

The full report is available at the Tropical Meteorology Project website.