The start of hurricane season is 6 weeks away, and four independent forecast outlets unanimously agree it will be a busy one.
Colorado State’s Bill Gray and protege Philip Klotzbach, the pioneers of seasonal hurricane forecasting, predict a blockbuster hurricane season, with 18 named storms, 9 hurricanes and 4 major hurricanes. (The 1981-2010 30-year averages are 12.1 named storms, 6.4 hurricanes, and 2.7 major hurricanes.)
“We anticipate an above-average Atlantic basin hurricane season due to the combination of an anomalously warm tropical Atlantic and a relatively low likelihood of El Niño,” Klotzbach and Gray write in their outlook, released last week.
(El Niño events typically suppress hurricane activity in the Atlantic by increasing wind shear that is hostile to storm development.)
The Colorado State duo not only predict a large number of storms, but also a high likelihood that a hurricane and, perhaps, major hurricane will make landfall along the Atlantic and/or Gulf coast. They say there’s a 72 percent chance a hurricane will strike the coast and a 61 percent chance of a major hurricane coming ashore.
“The probability of U.S. major hurricane landfall is estimated to be about 140 percent of the long-period average,” Klotzbach and Gray write.
The U.S. has avoided the landfall of a major hurricane in 7 consecutive seasons, the longest such period on record. Hurricane Wilma was the last major hurricane to strike the U.S. coast back on October 24, 2005.
“A wild season is on the way, and the ‘major hit drought’ on the U.S. coast should end,” meteorologist Joe Bastardi writes in the hurricane season outlook from WeatherBell, a private forecasting comapny.
Bastardi predicts 16 named storms, 12 hurricanes and 5 major hurricanes.
“I am very impressed with the pre-season set up,” Bastadi says in his outlook video. “The deep tropics this year are going to be much more active than last year.”
Although Bastardi predicts 3 fewer named storms than the 19 that formed in the 2012 Atlantic hurricane season, he expects the storms on average to be stronger and more energetic.
Bastardi forecasts the Accumulated Cyclone Energy (ACE) index – a metric of storm energy and longevity totaled across an entire hurricane season – to reach 165, well above 2012’s season total of 126. Interestingly, Klotzbach and Gray also predict an ACE of 165 for the 2013 Atlantic season. The median value over the period 1951-2010 is 92.4.
Above average tropical activity in the 2013 Atlantic hurricane season is also predicted by researchers at N.C. State University and forecasters at TropicalStormRisk.com, a private company in the United Kingdom. Here are their specific forecasts:
Number of named storms: N.C. State: 13 to 17, TropicalStormRisk.com: 15
Number of hurricanes: N.C. State: 7-10, TropicalStormRisk.com: 7.5
Number of major hurricanes: N.C. State: 3-6, TropicalStormRisk.com: 3.4
Taking the average of all four of these forecasts together, we get 16 named storms, 9 hurricanes, and 4 major hurricanes.
Four other organizations have yet to release their outlooks: NOAA, the UK Met Office, Penn State and Florida State. NOAA’s seasonal hurricane outlook is scheduled to be released May 23. Last year, the UK Met Office, Penn State and Florida State released their outlooks in late May or early June.
Are April hurricane outlooks skillful?
It’s reasonable to wonder whether these April hurricane forecasts are accurate. Last year, forecasters in April called for an average to quieter than normal season, and it turned out to be a busy year with 19-named storms, tied for the third most on record.
Seasonal forecasters emphasize the difficulties in predicting hurricane activity in April but say they have made progress in developing these predictions.
“Everyone should realize that it is impossible to precisely predict this season’s hurricane activity in early April,” Klotzbach and Gray write. “Our new early April statistical forecast methodology shows strong evidence over 29 past years that significant improvement over climatology can be attained.”
TropicalStormRisk.com says there is “no skill” in December forecasts for the hurricane season but that “[s]kill climbs slowly as the hurricane season approaches with moderate to good skill levels being achieved from early August.”
Hurricane season begins June 1 and ends November 30.