856 Late Season Tropical Cyclogenesis in the Western Caribbean Sea

Wednesday, 9 January 2013
Exhibit Hall 3 (Austin Convention Center)
Thomas J. Galarneau Jr., NCAR, Boulder, CO; and L. F. Bosart

The focus of this presentation will be on late season (October and November) North Atlantic tropical cyclogenesis events in the western Caribbean Sea, Gulf of Mexico, and Bay of Campeche. Tropical cyclogenesis events in these regions can pose a difficult forecast challenge since they occur i) in close proximity to landmasses, and 2) in conjunction with a wide variety of precursor disturbances. Examples of late season tropical cyclones (TCs) that formed in these regions during recent TC seasons include Wilma (2005), Lorenzo (2007), Paloma (2008) and Ida (2009). This presentation will focus on the rich spectrum of pre-genesis environments and will document the tropical and extratropical processes that are associated with the formation of late season TCs in the aforementioned regions.

A brief climatology of late-season TC events will be presented for the purpose of introducing selected pre-genesis environments and genesis physical mechanisms. These physical mechanisms include storm spin-up in regions of ambient low-level vorticity associated with: 1) the equatorward ends of decaying weak cold fronts, 2) ITCZ breakdowns, 3) trade-wind surges and gap winds, 4) upper-level potential vorticity streamers, and 5) convergence of monsoon westerlies with trade-wind easterlies. The results from one or two illustrative case studies drawn from the above-mentioned sample of TCs will be presented.

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