Case Study Analysis of Easterly Wave Formation in the East Pacific

Easterly waves are weak troughs of low pressure that propagate westward across the Atlantic and East Pacific. These disturbances seed the majority of East Pacific and Atlantic tropical cyclones. Most easterly waves originate from Africa, although recent work indicates that they can also be locally generated in the East Pacific. This study analyzed the development and origins of the two precursor disturbances that eventually became Hurricanes Patricia and John in the East Pacific. Using TRMM precipitation and ERA-I reanalysis datasets, we investigate the local processes responsible for the organization of vorticity and precipitation in the initial disturbances from which these tropical cyclones formed. It is shown that although the easterly wave that formed Hurricane John originated from Africa, interactions with the Gulf of Papagayo jet influenced the intensification of the disturbance. The disturbance that formed Hurricane Patricia strengthened through complex interactions with the Gulf of Tehuantepec wind jet. Our results support the contention that both local and remote influences contribute to easterly wave formation in the East Pacific Ocean.