A climatology of Kelvin waves in the Eastern Pacific and its role in extreme precipitation events in Southern Mexico and Central America

Considering the limited area and seasonality of occurrence, the eastern tropical north Pacific is one of the most prolific regions for tropical cyclones. These tropical cyclones are important for rainfall over the western coast of Mexico. Traditionally, the genesis of tropical cyclones have been linked to precursor easterly waves. After further analysis, there is strong evidence that convectively coupled atmospheric equatorial Kelvin waves (CCKWs) play an important role in such events.

A May-October climatology of CCKWs over the tropical eastern Pacific shows a relationship between CCKW passages and extreme precipitation events over southern Mexico. In addition to increased intense rainfall events over southern Mexico, CCKWs modulate tropical cyclogenesis activity over the eastern tropical Pacific.

A case study during late May 2008 is investigated to highlight the role of a CCKW passage resulting in increased precipitation over the eastern tropical Pacific. Low-level westerly winds were amplified over the tropical eastern Pacific and extended eastward over the western Caribbean after the passage of the CCKW. This westerly wind burst aided in the genesis of Tropical Storm Alma over the eastern Pacific and Tropical Storm Arthur over the western Caribbean