Characterization of the Variability of the Wet Season over Central America

Central America exhibits a distinct seasonal cycle of rainfall, which is objectively defined in this study as having an onset date and a demise date of the wet season on the first and the last day of the year when its daily rainfall exceeds and falls below the annual mean rainfall climatology. This is defined at both a regional scale and the granularity of the rainfall analysis dataset. Additionally, the methodology diagnoses the onset/demise dates of the wet season from an ensemble of 1000 members per season by perturbing the original time series to obtain robust probabilistic estimates. The variations in the onset date, demise date, seasonal length, and seasonal rain are considered with the variations of the El Niño Southern Oscillation, the Atlantic Warm Pool, and the Tropical East Pacific Warm Pool to better understand the influences of these large-scale climate variations. Our analysis reveals that these external factors have relatively less influence on the variations of the evolution of the wet season over Central America. It is shown that both onset and demise date variations have a bearing on the seasonal length and seasonal rainfall anomaly but impact them independently of each other. This study demonstrates that a seasonal outlook based solely on the onset date variations has useful prediction skills that portend for real-time monitoring of the onset date of the wet season.