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Hurricane Season forecasts updated: extreme weather-or-not

  AP Photo

All the various global weather sources that  make long-range predictions of the Atlantic and Caribbean hurricane season have updated their forecasts, the UK Met Office which waits until July to issue a forecast predicts 6 named systems. The season runs June 1st through November 30th.

The average or consensus of those 8 predictions is for a much quieter season than last year’s very active season, and on the low end of the long-term historical normal or climate average.

The mean of those forecasts is for 10 named systems, 6 hurricanes, and 2 major.

Those that attempt to figure out if and where any of those 10 storms will hit SOMEWHERE in the USA, agree that 3 will impact the United States.

I have not found any agreement on what part or parts of our coastline is favored over another, if any. But they feel there will be AT LEAST 1 major hurricane strike on the U.S. this season, how bad the impact will be on the affected area can’t be predicted this far in advance.

Last year was a very active season in the Atlantic tropical basin. There were 16 named storms, 8 hurricanes and 5 major hurricanes (Category 3 or above). Normally there are 11 named storms, 6 hurricanes and 2 major ones. The United States was impacted by 7 of the storms from July into September. Hurricane Gustav, which moved into Louisiana, was the highest rated storm at a Category 3. It was closely followed in September by Hurricane Ike, which moved inland near Galveston Texas. Although Ike was rated at a Category 2, it had a very large circulation that generated a large storm surge. The surge produced significant flooding along the coasts of Louisiana and Texas.

Looking ahead at the 2009 season we expect it to behave closer to the long-term averages. Last year there were two favorable ocean patterns that were in phase that contributed to higher storm numbers. First, the Atlantic Ocean was warmer than the long-term average sea surface temperatures. The warmer water helped to fuel thunderstorms, which are the initial building blocks of tropical storms. The warmer water along the tracks of tropical cyclones also helped any of the developing systems to grow or maintain their intensity.

Over the past winter and early spring seasons the Atlantic water in the tropical region has cooled off from the warm levels of last year. Some areas are colder than average, especially off the west coast of Africa. Although the water may return to warmer than normal values during the course of the summer and early fall, the season may start off more slowly than last year.

Another area that we monitor for seasonal tropical influence is the central Pacific area along the Equator. Last year this water was colder than normal and produced a weak La Nina episode. La Nina’s typically produce weaker winds aloft downstream in the tropical Atlantic area. Weaker winds aloft usually mean less wind shear is present to inhibit storm development.

This year the water in the Pacific has warmed to a Neutral or near normal phase. It is likely to remain in this Neutral phase during the summer, but some models are projecting that an El Nino will develop late this summer through the autumn. Should an El Nino phase develop as I expect (with warmer than normal water along the Equator in the Pacific), more wind shear would become likely over the tropical Atlantic area.

Based on these two ocean water influences, we expect that this tropical season will yield storm numbers close to the long term averages of 11 named storms, 6 hurricanes and 2 major hurricanes. Again the actual forecast for the 2009 season is 10, 6 and 2. The season should favor a lesser impact to the U.S. compared to last year’s heightened scenario. The cooler Atlantic waters will lower the threat while the potential for an El Nino forming by autumn could reduce the latter part of the season as more wind shear develops.

As we enter the active part of the tropical season in the months ahead, I will keep you up to date on any changes. Keep in mind it only takes one bad storm to make a devastating season for someone – no matter what the seasonal numbers turn out to be. And if storms hit outside the U.S. and/or don’t make headlines, people will think it was a quiet season even if the number total is high.


For more info: www.nhc.noaa.gov