Local Minimum of Tropical Cyclogenesis in the Eastern Caribbean
Owen H. Shieh, Cornell University, Ithaca, NY; and S. J. Colucci
The study has determined that a local, climatological minimum of tropical cyclogenesis exists over the eastern Caribbean Sea. This area, known colloquially by forecasters as the “hurricane graveyard,” is located within the belt of tropical easterlies during most of the Atlantic hurricane season, which lasts from June through November. Tropical easterly waves emerging from the African continent usually follow a path through the Lesser Antilles and into the eastern Caribbean. GOES infrared satellite imagery shows that easterly waves frequently exhibit warming cloud tops and decreasing convection in an area bounded by the islands to the north and east, Venezuela to the south, and roughly 75 degrees longitude to the west. QuikSCAT derived surface winds during clear-sky conditions frequently show the presence of accelerating easterlies in the central Caribbean as part of the Caribbean Low-Level Jet (CLLJ). Analysis of the NCEP global reanalysis wind fields suggests the presence of an area of persistent low-level mass divergence in the eastern Caribbean. This implies a subsident regime that would weaken convection. Climatologically, this phenomenon reaches peak intensity in July, then shifts towards the east and weakens in the latter half of the Atlantic hurricane season. This is reflected by the local minimum of tropical cyclogenesis points in the National Hurricane Center's best track data in the early part of the season. El Niño directly affects the strength of the CLLJ, and hence, is related to the intensity of the low-level divergence in the eastern Caribbean. The local minimum of tropical cyclogenesis in this region has important implications to operational forecasting, since the vast majority of tropical cyclones in the Caribbean eventually affect surrounding landmasses.
Poster Session 1, Student Conference General Poster Session
Sunday, 20 January 2008, 5:30 PM-7:00 PM, Exhibit Hall B
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