Sea-Surface Temperature and Deep Convection as a Paired Predator-Prey System in the Caribbean Sea and Gulf of Mexico Prior to and During Tropical Storm Cindy in June 2017 Using GHRSST MUR Level 4 Global Foundation SST Analysis, A-Train and Geostationary Satellite, and ECMWF-Interim Reanalysis Data

Abstract:

Tropical ocean-atmosphere interactions, particularly the interplay between sea-surface temperature (SST) and convection, are critical not only for characterizing large-scale oscillations, but even for finer spatial and temporal time scales such as individual convective events, including tropical cyclones (TCs). Here, using the field campaign period of the Convective Processes Experiment (CPEX) as an impetus for study, this analysis provides insights on possible precursors to the development of Tropical Storm (TS) Cindy, which became a named storm on 19 June 2017 over the Gulf of Mexico, following an enhanced period of convection for more than one week in much of the Caribbean Sea. The warm waters of the Caribbean, as shown by the high resolution GHRSST MUR Level 4 Global Foundation SST Analysis (MUR hereafter), are transported northward into the Gulf of Mexico (GoM), several days prior to the emergence of a tropical low and then TS Cindy into the GoM. Hovmoller diagrams indicate that the axis of maximum SSTs longitudinally averaged between 265° and 280° leads the axis of maximum deep convection as observed by MODIS by several days.

A Predator-Prey (Lotka-Volterra) nonlinear system of equations, with SST the prey and deep convection the predator, is tested on the synoptic timescale of the tropical cyclone development. The main source term of convection, (-dSST/dt), maximizes during the onset of Cindy, and the Predator-Prey system qualitatively explains the high cloud field which is most prolific to the north, east, and south of the minimum sea-level pressure. Minimum dSST/dt is observed just north of the center of Cindy on 20 June, the day of greatest deepening of the tropical storm.

Prior to, during, and after TS Cindy, we also compare the Predator-Prey calculated convection using SSTs from MUR against the SSTs from reanalysis data, whose SST maxima occur approximately 1-2 days later. While enhanced upward surface latent heat fluxes are present up to 10 days prior to the formation of TS Cindy over the Caribbean Sea, enhanced upward surface sensible heat fluxes only emerge just prior to and during the strengthening of TS Cindy. Finally, the horizontal structure of SST and dSST/dt within and adjacent to TS Cindy is assessed for its role in possible internal dynamics of the tropical storm, with potential implications for other TCs.