Posted: 11:16 am Wednesday, December 7th, 2011
By Eliot Kleinberg
Posted 10:15 a.m. Dec. 7, 2011
Just days after the Nov. 30 end of the 2011 hurricane season, the soothsayers at Colorado State University are out with their forecast for next year.
But, for the first time in its 29 years, the team is limiting its December guess to just probabilities, rather than suggesting the number of tropical storms that will form, which will become hurricanes, and which of those will be major hurricanes.
That’s because guesses this far out “have not proved skillful in real-time over the last 20 years,” the team of Philip Klotzbach and William Gray said Wednesday.
It’s too early to know what El Niño — the warm water phenomenon that tends to hinder hurricane activity — will do between now and next summer, “so we’re going to look instead at analyzing factors that influence the hurricane season rather than actually predicting the number of hurricanes,” Klotzbach said in a release.
“There is significant uncertainty with this earliest outlook, issued six months prior to the start of the hurricane season, so we’re looking more at a range of different potential outcomes which might occur,” Gray said. He said the team still believes the tropics are still in a multi-decade period of above-normal hurricane activity.
The team looked at both El Niño and “Atlantic thermohaline circulation,” or THC, the phenomenon of warm surface water flowing northward and cold deep water flowing southward. When it’s stronger than normal, water temperatures tend to be warmer, vertical wind shear tends to be reduced, sea level pressures tend to be lower, and mid-levels of the atmosphere tend to be moister, all of which favor a more active season.
The team predicted:
• A 45 percent chance of an above-average THC and no El Niño development, raising hurricane activity to about 140 percent of the average season, with 12-15 named storms, seven to nine hurricanes, and three to four major hurricanes.
• A 30 percent chance of an above-average THC and a “significant” El Niño, reducing hurricane activity to about 75 percent of the average hurricane season — eight to 11, three to five, and one to two.
• A 15 percent chance of an “unusually strong” THC and no El Niño, bringing activity nearly double the average — 14 to 17, nine to 11, and four to five.
• A 10 percent chance of a weak THC and a a significant El Niño, bringing activity at 40 percent of the average season, or five to seven named storms, two to three hurricanes, and zero to one major hurricane
The team plans to return to posting hard numbers with its April 4 forecast. It issues another on June 1, the official start of the hurricane season, and on Aug. 3. The season runs from June 1 through Nov. 30.
The Gray-Klotzbach team, and other season prognosticators, continually stress that season forecasts are of interest mostly as mental exercises and should have no impact on how people prepare for hurricane season.
They cite as examples this past year, which tied with 2010, 1995 and 1887 for third busiest on record, but which got little attention because only Irene was a newsmaker. And the 1992 season, which produced only seven named storms, among them the catastrophic Andrew.
They remind people in hurricane zones that there’s no magic number above which the world is going to end and below which they are completely safe. Residents are urged to prepare every year as if at least one hurricane will hit them, which of course could happen in either a busy year or a quiet one.