Interannual Variability of the Early and Late Rainy Seasons in the Caribbean

An important understanding of the Caribbean rainfall cycle is its interannual variability. To address this issue, this study conducts: (i) a temporal composite of the annual cycle of precipitation during anomalously wet and dry years across 34 Caribbean stations using daily observed precipitation data; and, (ii) a spatial composite of SST, SLP, and mean flow convergence in the Caribbean using the NCEP/NCAR reanalysis, NOAA v5 Extended Reconstructed SST, and ERA-Interim Reanalysis datasets. This study finds that the Early-Rainy Season (ERS) and Late-Rainy Season (LRS) are predominantly independent of each other, highlighting that most wet or dry years in the rainfall cycle are a result of anomalous precipitation from only one component of the rainfall season. Dry (wet) ERS years are due to a preceding positive (negative) NAO induced cold (warm) SST persistence signal across the Caribbean that produces a wind-evaporation-SST (WES) feedback of enhanced easterlies (westerlies) and moisture divergence (convergence). Dry (wet) LRS years are due to the summertime onset of a positive (negative) ENSO phase which produces a WES feedback of anomalous cool (warm) SSTs, high (low) pressure, easterlies (westerlies), and moisture divergence (convergence) in the Caribbean. The seasonal evolution of the NAO-SST persistence signal and ENSO affect the climatological dynamical mechanisms that shape the Caribbean’s regional rainfall cycle. They also explain why the NW Caribbean has weaker rainfall variability signal than the rest of the Caribbean. Finally, mature ENSO phases in the preceding seasons weakly modify the Caribbean ERS, while a persistent NAO-SST signal can be a secondary influence on the duration of anomalous precipitation in the Caribbean LRS.