The Inactive 2009 Hurricane Season In the North Atlantic Basin: An Analysis of Environmental Conditions

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The 2009 North Atlantic hurricane season was below normal when considering overall hurricane activity; however, activity was seen to vary sharply from month to month. All activity in 2009 occurred from August through early November with the highest activity in August, less activity in September and October, and only one tropical cyclone in November. Therefore, the 2009 hurricane season had a late start with no storms occurring in June and July. For the 2009 season, it is shown that large scale environmental factors forced by the El Niño event, such as increased vertical wind shear across the Caribbean and decreased mid-tropospheric relative humidity in the Main Development Region (10° N to 20° N and 20° W to 60° W), contributed strongly to the observed patterns of tropical cyclone activity across the basin. Lastly, the activity in the Atlantic in 2009 is compared to that in the Eastern North Pacific Western Development Region (10° N to 20° N and 116° W to 180°), and the potential for long-range seasonal forecasting of Atlantic tropical cyclones is noted.

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National Weather Digest, v. 34, issue 2, p. 117-128