Tropical Depression	Category 1	Category 3	Category 5
Tropical Storm	Category 2	Category 4

2009 Atlantic Basin Tropical Summary (continued)

2009 Atlantic Basin Hurricane Season Summary

2009 will go into the record books as a very uneventful hurricane season, except for late season Ida. The question "why was it so quiet" always arises as a season like this one comes to an end, especially after a series of very active years. Hindsight is sometimes 20/20 so I will give my hindsight "opinion" of what happened. But the prediction of the occurrence of the following features is not at all easy to forecast or extrapolate before it happens! There are two primary reasons for the quiet season in my opinion;

1) The mid-latitude westerly winds were much farther south than normal and this southward displacement caused three upper level wind features across the Gulf Caribbean and Atlantic to also be shifted south. The diagram below shows the three upper level circulation features, only one is readily conducive to tropical cyclone formation (the Subequatorial Ridge) and it was displaced south of the typical genesis area and where tropical waves normally track.

Average position of upper level weather features in summer/early fall across the tropical and subtropical Atlantic. Black: non-tropical west winds. Yellow: Subtropical Ridge. Red: Tropical Upper Tropospheric Trough (TUTT). Green: Subequatorial Ridge.


As in the figure above, except for summer/early fall 2009

The TUTT caused shear, and the Subtropical Ridge, although typically a region of light wind shear, caused sinking air. Neither of these circulations typically favors tropical cyclone formation, and they did not in 2009.

2) El Nino unfolded and became more prominent through summer and fall. The basic result was to increase west wind shear across the Caribbean Sea and southwest tropical Atlantic and also to cause anomalous sinking motion across the same area. Neither favored tropical cyclone development.

The combination of these two ingredients made for many atmospheric snares for the tropical cyclones that did develop and hence they were for the most part very short-lived. This combination also routinely formed snares that prevented tropical cyclone formation on many days during the peak of hurricane season.

The predictive skill of seasonal outlooks varies from one year to the next and this year is no exception. Bill Gray and Phil Klotzbach started with a forecast of 14 named storms in December, but that number shrank to 12 in April, 11 in June and 10 by August. The hurricane forecast was no different shrinking from 7 in December to 6 in April, 5 in June and finally to only 4 in August. The trend was correct but the initial forecast was well above what has occurred so far and time is running out.

The 2009 Atlantic Basin hurricane season, at least on paper, does not seem as quiet as it appeared to most of our viewers and coastal residents. There were 9 named storms (the average is 10), but only 3 became hurricanes (the average is 6). Two of the hurricanes became major hurricanes (the average is 2); Bill reached Category 4 intensity and Fred reached Category 3 intensity, while Ida reached Category 2 intensity. The list of nine named storms and two tropical depressions is shown below.

Only Tropical Storms Claudette and Ida made landfall in the U.S. thus far (1 in the Florida Panhandle and the other in southern Alabama near the Florida border). There have been no U.S. hurricane strikes. 8 of the 11 tropical cyclones lasted less than four days and 5 of these lasted two days or less. Only Ana and Bill lasted more than 5 days; Bill being the only true "long-track" Atlantic hurricane of 2009 lasted about 9 days.

Tropical storm Grace formed in the NE Atlantic and goes into the record books as the farthest north tropical storm formation (without first being a subtropical storm). From the track map below it is obvious all named storms, except Claudette, have thus far formed in the Atlantic. Only Anna and Erika have briefly entered the NE Caribbean Sea. So based on tropical storm duration and track behavior it was a very quiet hurricane season for most land areas, including the U.S. This was the quietest hurricane season since 1997 (7 named storms and 3 hurricanes) and the second quietest in the 1995 to 2009 "active era" in terms of storms and hurricanes. The last time there were only 2 hurricanes was back in 1992. There remains a small portion of hurricane season yet to come, so we say always be prepared just in case.

This 2009 hurricane season (tracks above) has thus far been very kind to the U.S. with only minor damage from Claudette and moderate damage from Ida after it turned into a Nor'easter along the East Coast. This allowed insurance coffers to refill without any major Hurricane hits. This is generally a good thing, because when insurance companies lose money rates go up!