Update – 2011 Hurricane Season

10 08 2011

I know a lot of you are wishing for a Tropical Storm or a Hurricane.  The thought is that will provide us much needed rain and cool the temperatures.  That might be the case, but wishing for a tropical system to make a direct hit on the Houston-Galveston area sounds a bit dicey to me.  We are now about halfway through the 2011 Hurricane Season, and except for some excitement caused by Tropical Storm Don, not much has developed out in the Atlantic so far. 

However, the National Oceanic and Atmospheric Administration (NOAA), through its Climate Prediction Center, has recently published its 2011 Updated Atlantic Hurricane Season Outlook.   As issued on August 4th, a summary of the Outlook is found below:

NOAA’s updated 2011 Atlantic Hurricane Season Outlook calls for an 85% chance of an above-normal season, and a 15% chance of a near-normal season. There is no expectation for a below-normal season. Therefore, 2011 is expected to become the twelfth above-normal season since 1995. This updated outlook reflects a higher likelihood of an above-normal season compared to the pre-season outlook issued in May, which indicated a 65% chance of an above-normal season. See NOAA definitions of above-, near-, and below-normal seasons. The Atlantic hurricane region includes the North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico.

The higher confidence of an above-normal season is based on several factors. First, as predicted in May, conducive atmospheric and oceanic conditions are now in place over the tropical Atlantic Ocean and Caribbean Sea (called the Main Development Region- MDR). Second, these conditions are expected to persist throughout the peak months (August-October) of the hurricane season in association with the tropical multi-decadal signal, which has contributed to the high activity era that began in 1995. Third sea-surface temperatures in the MDR are the third warmest on record, and models predict a continuation of very warm SSTs through the hurricane season. Fourth, there is a possibility of La Niña re-developing.

Historically, this combination of conditions produces an active Atlantic hurricane season. In addition, several dynamical model forecasts of the number and strength of tropical cyclones indicate that an above normal season is likely.

The 2011 season is expected to be comparable to a number of active seasons since 1995. We estimate a 70% probability for each of the following ranges of activity during 2011:

  • 14-19 Named Storms
  • 7-10 Hurricanes
  • 3-5 Major Hurricanes

The official NHC seasonal averages are 11 named storms, 6 hurricanes, and 2 major hurricanes. To date, five tropical storms (Tropical Storms Arlene, Bret, Cindy, Don, and Emily) have formed in the Atlantic basin. Significant activity is expected for the remainder of the season, with an additional 9-14 named storms likely, of which 7-10 are expected to become hurricanes with 3-5 reaching major hurricane status.

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