Central America exhibits a distinct seasonal cycle of rainfall, which is objectively defined 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 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 timeseries to obtain robust probabilistic estimates. We show 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. We demonstrate 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.