Influence of the Madden-Julian oscillation on Costa Rican mid-summer drought timing

The Central American mid‐summer drought (MSD) is the decline of precipitation during the middle of the wet season (July and August) over Central America and southern Mexico. It affects agriculture and favours the initiation of bushfires in Costa Rica's national parks, particularly during El Niño years. The MSD is a seasonal phenomenon that varies in intensity and timing inter‐annually. The Madden–Julian oscillation (MJO) has been shown to influence Costa Rican rainfall on intra‐seasonal time scales, and therefore may be important to the MSD. In this study we use rainfall data from seven stations in Costa Rica to analyse the MJO's influence on the timing of the onset and end of the MSD. We find that the MSD is more likely to start and end in MJO Phases 1 and 8, respectively. Our findings indicate enhanced MSD predictability on intra‐seasonal time scales, which could be beneficial to agricultural planning in Costa Rica.