Abstract
Prior to tropical cyclogenesis events in the western Caribbean region, low-level jets in the Caribbean and eastern North Pacific (EPAC) exhibit differences from climatology. Combined with local topography, the Caribbean Low-Level Jet (CLLJ) and Choco low-level jet modulate low-level convergence and precipitation. Using reanalysis and satellite data, low-level wind and outgoing longwave radiation (OLR) are analyzed in the pre-genesis environment of 85 western Caribbean genesis cases. A significant westerly zonal wind anomaly extends from the southwestern Caribbean into the EPAC, corresponding to a weaker CLLJ and a stronger westerly component of the Choco jet. Concurrently, a significant southerly meridional wind anomaly centered around Panama indicates a northward extension of the Choco jet with a stronger southerly component, resulting in moisture transport into the southwestern Caribbean. Combined with a weaker western branch of the CLLJ, this leads to enhanced convection in the western Caribbean prior to genesis. These significant low-level wind and OLR anomalies are still evident after excluding genesis cases preceded by the westerly phases of the Madden–Julian Oscillation (MJO), albeit developing closer to genesis than westerly MJO cases. A westward-propagating negative OLR anomaly indicates these cases are also frequently associated with African easterly waves (AEWs). A case study of pre-Hurricane Ida (2021) supports these findings, in which a rapidly weakening western branch of the CLLJ and enhanced cross-Panama flow from a strong Choco jet helped initiate and sustain a mesoscale convective system in the southwestern Caribbean, later undergoing genesis after becoming embedded within a passing AEW.