Monday, November 30, 2009

Hurricane Season 2009 Ends

November 30th marks the official end of the 2009 Atlantic Hurricane Season, which began June 1st. Here's a recap of this year's storms:

Tropical Depression One
Tropical Storm Ana
Hurricane Bill (max Category: 4)
Tropical Storm Claudette
Tropical Storm Danny
Tropical Storm Erika
Hurricane Fred
(max Category: 3)
Tropical Depression Eight
Tropical Storm Grace
Tropical Storm Henri
Hurricane Ida (max Category: 2)

That's nine named storms, three of which became hurricanes, two of which were major hurricanes. An "average" tropical season has 10.1 named storms, 5.9 hurricanes, with 2.5 of those becoming major hurricanes at Category 3 strength or greater.

So that means 2009 was slightly below-average for the number of named storms, with only half the average number of hurricanes. Still, of those few hurricanes that did form this year, two of them became major, which is about average.

We've talked about this previously on the blog, but El Nino is possibly one of the factors impacting the reduced number of tropical cyclones able to strengthen to hurricane status. The El Nino in the equatorial Pacific has been strengthening through the Summer and Fall months, which alters the upper-level wind patterns globally. This led to more wind shear (different wind speeds at different heights and directions) in the Atlantic, Caribbean, and Gulf, which disrupted cyclone organization. Shear prevents cyclones from strengthening uninhibited. Instead, the shear acts to "rip apart" the cyclone circulations, keeping most of this year's storms below hurricane status.

You can get the weekly update (Mondays) on El Nino here.

1 comment:

Anonymous said...

Thanks a lot for the post and the link to NOAA.