An Analysis of Central American Gyres

Monsoon gyres, commonly found over the western Pacific Ocean, are characterized by broad low-level cyclonic circulations that occur at a variety of spatial scales ranging from 1500-3000 km. Low-level cyclonic gyre circulations, although much less frequent than their western Pacific counterparts, have also been observed over Central America during the latter half of the tropical cyclone (TC) season when TC genesis is favored over the western Caribbean and Gulf of Mexico. A noteworthy gyre observed during the 2010 PREDICT field project served as a “collector” of TC Matthew and a source for TC Nicole. Another gyre during October 2011 was associated with devastating flooding in Guatemala and El Salvador when TD 12-E made landfall on the Pacific coast of Central America. These gyre occurrences, their apparent links to TC activity, and their association with high-impact weather motivates this presentation.

A limited analysis of Central American gyres suggests that their spatial scales vary between 1500-2000 km. These gyres also tend to be co-located with reservoirs of deep moisture that are characterized by high precipitable water values (>50 mm) and embedded deep convection on their southern and eastern sides. Catastrophic flooding can occur when the gyre circulation, containing this deep reservoir of tropical moisture and convection, interacts with the high and rugged terrain of Central America.

The purpose of this presentation will be to present a Central American gyre climatology to include gyre frequency, duration, and intensity. The climatology will include an evaluation of how TC genesis occurs in gyre environments. Emphasis will also be placed on documenting and understanding gyre formation and evolution, including the role of tropical and mid-latitude circulations in the process. The impact of local and regional Central American topography in enhancing cyclonic vorticity within a gyre will also be considered. Gyre development and evolution will also be analyzed within the context of synoptic, intraseasonal, and interannual circulations in the tropics to include convectively coupled Kelvin waves, the Madden-Julian Oscillation, and the El Nino-Southern Oscillation (ENSO).