Seasonal Climatology and Dynamical Mechanisms of Rainfall in the Caribbean

The Caribbean is a complex region that heavily relies on its rainfall cycle for its economic and societal needs. Its high reliance on rainfall makes the Caribbean especially susceptible to hydro-meteorological disasters (i.e. droughts and floods). Numerous studies have investigated the seasonal-cycle of rainfall in the Caribbean with temporal resolutions that can mask the seasonal transitions and regional differences of rainfall, which has resulted in inconsistent findings. In addition, the mechanisms that shape the rainfall cycle are not fully understood. To address these problems, this study conducts a principal component analysis across 38 Caribbean stations using higher time resolution data from the Caribbean Institute of Climatology and Hydrology and National Oceanic and Atmospheric Administration Global Historical Climatology Network datasets. This study also uses the ERA-Interim Reanalysis to conduct the first-ever total moisture budget for the Caribbean. This study suggests that the seasonal cycle of rainfall in the Caribbean is hinged on three main sources of moisture convergence: the Eastern Pacific ITCZ, the Atlantic ITCZ, and one not identified in previous studies, the western flank of the North American Subtropical High (NASH). The Atlantic Warm Pool (AWP) and Caribbean Low-Level Jet (CLLJ) modify the extent of moisture by these main sources in the Caribbean. The zonal migration of the western flank of NASH due to the expansion and contraction of NASH results in the bimodal rainfall pattern seen in the NW Caribbean and most of the central Caribbean. The meridional migration of the Eastern Pacific ITCZ and its interactions with NASH results in the bimodal pattern of rainfall in the western Caribbean. This study is the first to define the Atlantic ITCZ as the major source of moisture for the central and southern Lesser Antilles and is responsible for their unimodal rainfall pattern. Transient convergence is marginal in the Caribbean; therefore, tropical cyclones and easterly waves are likely to have marginal contributions to the climatological rainfall cycle in the Caribbean. Transient divergence by U.S. mainland mid-latitude features is responsible for the early demise of the Late-Rainy Season (LRS) in the NW Caribbean. Finally, this study provides the framework to understand the variations of Caribbean rainfall patterns and dynamical processes on interannual to multi-decadal timescales, provides insight into the causes and how one might predict hydro-meteorological disasters in the Caribbean, and demonstrates the importance of using higher temporal data for the Caribbean.