The Development and Breakdown of a Central American Gyre: A Precursor to Hurricane Patricia

Central American Gyres (CAG) are large cyclonic circulations which develop over Central America during the early and late period of tropical cyclone season in the Western Hemisphere. These convectively active features often lead to significant rainfall across Central America and Southern Mexico, resulting in societal disruption. CAG's can also act as precursors to tropical cyclone (TC) development over the Caribbean Sea, Gulf of Mexico, or the Eastern North Pacific. The goal of this study is to document the formation and breakdown of a CAG which influenced the development of Hurricane Patricia, one of the most intense hurricanes in the history of the western hemisphere.

Preliminary evaluation suggests that a CAG was classifiable from 0600 UTC 16 October – 0600 UTC 19 October, 2015. Potential features related to the development of the CAG to be examined include: building surface high pressure over the southeast United States which contributed to gale force gap winds over the Gulf of Tehuantepec, the accumulation of easterly wave energy propagating into Central America, and the active phase of the Madden Julian Oscillation aiding convection over Central America. Preliminary examination suggests that gale force gap winds over the Gulf of Tehuantepec interacted with the eastern North Pacific monsoon trough and aided in the development of a low pressure circulation southeast of the Gulf of Tehuantepec on 18 October, 2015. This low pressure circulation was initially embedded within the larger scale CAG circulation. As the CAG circulation broke down on 19 October, 2015, this low pressure circulation southeast of the Gulf of Tehuantepec continued to gradually develop. Ultimately, this low pressure center was classified as a TC on 20 October, 2015. While the ongoing gap wind event initially contributed to increased low level vorticity near the TC, it also resulted in dry air entrainment that inhibited additional development while TC Patricia was still east of the Gulf of Tehuantepec. Once TC Patricia moved west of the Gulf of Tehuantepec, the negative influence of dry air was no longer a factor and the TC rapidly intensified while moving into a more favorable environment characterized by moist mid levels, low vertical wind shear, warm sea surface temperatures in excess of 30° C, and anomalously high oceanic heat content.