Influence of the Caribbean Low-Level Jet and Topography on the Pre-Genesis Environment of Hurricane Ida (2021)

Even though many Caribbean tropical cyclones (TCs) impact land, the formation and amplification of easterly waves in the Caribbean basin and the resulting influence on Caribbean TC genesis is a relatively understudied phenomenon. One factor in Caribbean TC genesis is the Caribbean Low Level Jet (CLLJ). Previous research has shown that the reversal of the meridional PV gradient associated with the CLLJ can lead to the formation or amplification of easterly waves, and a strong CLLJ is correlated with increased TC genesis in the East Pacific. Conversely, a strong CLLJ is often associated with decreased TC genesis in the Caribbean basin due to increased vertical wind shear and low-level moisture divergence, but research on its effects below seasonal timescales is lacking.

In 2021, the NASA CPEX-AW field experiment observed the environment in and around a weak easterly wave in the central Caribbean. In less than two days, the wave intensified and underwent TC genesis in the Northwest Caribbean much sooner and further northward than previously anticipated. An evaluation of the pre-genesis environment of this wave, which eventually intensified into Hurricane Ida, revealed two main genesis factors: the northward propagation of a topographically induced mesoscale convective system (MCS) and associated relative vorticity from just offshore of South America, and a breakdown of the CLLJ from anomalously strong to weak occurring concurrently with the amplification of the easterly wave. In this study, we examined the potential impact of the CLLJ and the topographic environment of the Caribbean on the observed wave amplification event that preceded the genesis of Hurricane Ida, and show how a deeper understanding of the dynamics surrounding such events are important for future predictability of Caribbean TC genesis.