Atmospheric Circulation over the East Pacific and Caribbean Tropical Cyclogenesis

Tropical cyclone (TC) genesis in the Caribbean (July–October) is examined using composites of 44 storms (1979–2025) from model-assimilated in situ and satellite observations. Results identify how the atmospheric circulation over the East Pacific affects Atlantic TC activity. A zonal overturning cell over the Amazon is linked to a conveyor of tropical 150–200 hPa easterly winds (U 200), supported by a sea surface temperature dipole pattern. Convective activity over the Eastern Caribbean is significantly correlated with accumulated cyclone energy (ACE) and U 200 airflow (7–17° N 45–80° W). Upper easterlies in late summer precede cool-phase El Niño–Southern Oscillation (ENSO) and show a long-term trend of −0.08 m s−1/yr favoring TC genesis during the satellite era. Lag correlations reveal that daily upper winds lead convection by four days, reflecting westward-intensifying tropical waves. Composites of the 10 most active summers exhibit low-level westerly anomalies (~2 m/s) across Central America, a northward shift in salinity fluxes and the equatorial trough, and meridional overturning cells ascending over the Caribbean and subsiding over the Amazon. Oceanic responses include a weakening of the Caribbean Current and enhanced upwelling in the East Pacific and Atlantic. Global composite analyses reveal a westward-propagating Walker circulation moving at ~0.26 m/s, associated with an ocean Rossby wave during La Niña onset. The pulling effect of upper winds over the East Pacific ‘ride’ above negative sensible heat fluxes (−1011 W) from an expanding cold tongue. The downstream winds enhance upstream divergence at 150–200 hPa, while the surface fluxes create a deep thermodynamic ‘sink’. Together these statistical commonalities offer diagnostic guidance on TC genesis in the Caribbean.