Subseasonal Prediction of the Rainy Season and the Midsummer Drought in Mesoamerica

The seasonal cycle of rainfall in Mesoamerica exhibits complex features such as the Midsummer Drought (MSD) that greatly influence local agriculture and motivate diagnosing the potential of its subseasonal prediction. This study evaluates state-of-the-art S2S forecast systems for their representation of the rainy season through their climatology and forecast skill. These models reasonably capture the main features of the rainy season, such as onset and retreat dates, as well as the MSD characteristics. However, they overestimate the MSD duration by 5–10 days. Forecast skill for weekly precipitation is low beyond week 2, whereas rainy season onset and retreat remain predictable past 25 days, especially for the European Center for Medium-Range Weather Forecasts and United Kingdom Met Office forecasts. MSD onset forecasts are more skillful than MSD end forecasts, suggesting different modulating processes for each date. Because of the significant influence of the El Niño-Southern Oscillation (ENSO) on the variability of MSD, we evaluate its effects on predictability and forecast skill. La Niña increases precipitation and enhances predictability and prediction skill of precipitation from June to September, whereas El Niño reduces mean rainfall and forecasts are more skillful during the MSD-periods. These results highlight ENSO’s role in subseasonal forecasting and suggest that ENSO phase information could help improve decision-making in planning sowing dates and regional water resource management.