Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 4:45 PM GMT on May 22, 2007
It's going to be a very active 2007 hurricane season in the Atlantic, according to NOAA's seasonal forecast issued today. The NOAA team predicts a very high (75% chance) of an above-normal hurricane season, a 20% chance of a near-normal season, and only a 5% chance of a below-normal season. They expect 13-17 named storms, 7-10 hurricanes, and 3-5 major hurricanes (a normal season has 10-11 named storm, 6 hurricanes, and 2 intense hurricanes). Most of these storms are expected during the usual August-October peak of hurricane season, but NOAA does not give any breakdown of which portions of the coast are more likely to be affected. They give two reasons for predicting an above-normal hurricane season:
1) A continuation of conditions since 1995 that have put us in an active hurricane period (in particular, the fact that sea surface temperatures in the Atlantic Main Development Region for hurricanes are currently about 0.6 C above normal, Figure 1).
2) The strong likelihood of either neutral or La Niña conditions in the tropical Pacific Ocean.
Figure 1. Top: Tropical Atlantic Ocean temperatures in the Main Development Region for hurricanes (green box) were 0.6 C above average during March and April 2007. This anomalous warmth is expected to persist though hurricane season. Bottom: The 0.6 C above average temperatures are consistent with the exceptionally warm temperatures seen since 2003. Image credit: NOAA.
How good are these forecasts?
NOAA's long lead hurricane outlook team, which consists of scientists from NOAA's Climate Prediction Center (lead: Gerry Bell), National Hurricane center (NHC), and the Hurricane Research Division (HRD), have been making seasonal hurricane forecasts since 1998. If one grades their May forecasts based on predictions of a below average, average, or above average season, NOAA has done pretty well. Seven of their nine forecasts have been correct. Their only failures occurred last year, when they called for a very active season (it was a normal year, with 10 named storms, 5 hurricanes, and 2 intense hurricanes), and 2001, when they called for a normal year (it was a very active year, with 15 named storms, 9 hurricanes, and 4 intense hurricanes).
Steering currents for June
It's now possible to say something about the steering currents for the upcoming Atlantic hurricane season, which officially begins June 1. A hyperactive Atlantic hurricane season is no big deal if the steering currents are your friend! The forecast jet stream pattern for the next two weeks from the GFS model is similar to last year's pattern. I expect we'll see a series of troughs of low pressure marching across the Atlantic Ocean through early June, which is typical for this time of year. The Bermuda High is in its usual location, and there are no signs of the unusual steering pattern of 2005 that brought so many hurricanes over the U.S.. It is still to early to say what the steering patterns will do during peak hurricane season, August through October, though.
The Dr. Bill Gray/Phil Klotzbach's team at Colorado State University issues their updated Atlantic hurricane season forecast on May 31 next week, and I'll be sure to make a post about that forecast.
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