Review of Regional Weather for April 2023
1.1 During April 2023, below- to near-average rainfall was recorded over Mainland Southeast Asia, with a mix of below- to above-average rainfall over the Maritime Continent. Over Mainland Southeast Asia, below-average rainfall was recorded over most of the central and southern part of the region with the largest negative anomalies (drier conditions) over southern Thailand. Elsewhere in Mainland Southeast Asia, the rainfall was near-average. Over the Maritime Continent, the largest positive anomalies (wetter conditions) were recorded over southern Sumatra with the largest negative anomalies over parts of Borneo for both the GSMaP-NRT (Figure 1, left) and CMORPH-Blended (Figure 1, right) satellite-derived rainfall estimates.
1.2 The observed rainfall anomaly pattern of below- to near-average rainfall over Mainland Southeast Asia, below-average rainfall over central Maritime Continent , and no widespread regional anomalies elsewhere over the Maritime Continent, is broadly consistent with the predictions from the subseasonal weather outlooks for April 2023 (3 – 16 April 2023 and 17 – 30 April 2023).
1.3 Above-average temperatures were recorded over most of Mainland Southeast Asia, with near- to above-average temperature over most of the Maritime Continent. The warmest anomalies (more than 2 °C above-average) were recorded over parts of Lao PDR and northern Thailand.
2. Climate Drivers
2.1 The Madden-Julian Oscillation (MJO) was active during April 2023. An MJO signal propagated eastwards from the Maritime Continent (Phase 5), reaching the Western Hemisphere (Phases 8 and 1) during third week of April, and then just entering again the Maritime Continent (Phase 4) at the end of the month. Typically for April, Phases 7, 8, and 1 bring drier conditions to the Southeast Asia, while Phases 3 to 5 bring wetter conditions, particularly in southern Southeast Asia.
2.2 The tropical Pacific was in an ENSO neutral state during April. Overall, sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean indicated neutral conditions.