Review of Regional Weather for June 2023
1.1 During June 2023, a mix of below- to above-average rainfall was recorded over the ASEAN region. Over Mainland Southeast Asia, above-average rainfall was recorded in the eastern parts of the region, while a mix of below- to above-average rainfall was recorded over the rest of the region. Over the Maritime Continent, above-average rainfall was recorded over the western Maritime Continent, with a mix of below- to above-average rainfall elsewhere. The largest positive anomalies were over northeastern 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 the ASEAN region is broadly consistent with the predictions from the subseasonal weather outlooks for June 2023 (29 May – 11 June 2023, 12 – 25 June 2023 and 26 June – 9 July 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. Near- to below-average temperatures were recorded over the southern Maritime Continent. The warmest anomalies (more than 2 °C above-average) were recorded over southern parts of the Malay Peninsula, Lao PDR and northeast Thailand.
2. Climate Drivers
2.1 A Madden-Julian Oscillation (MJO) was active at the start of June 2023. An MJO signal propagated eastwards from the Western Hemisphere and Africa (Phase 1) and to the Indian Ocean (Phases 2 and 3) in the first half of June. In Week 3, the MJO signal weakened and became insignificant. An MJO signal re-emerged in Week 4 over the Western Hemisphere and Africa (Phase 1) and propagated eastwards to the Indian Ocean (Phase 2). Typically for June, Phases 1 and 2 tends to bring drier conditions in northern Southeast Asia while Phases 2 and 3 tend to bring wetter conditions to the western Maritime Continent.
2.2 Over the past month, there have been signs of El Niño-like conditions. El Niño sea surfaces temperatures indices are near or exceeding El Niño thresholds, whereas key atmospheric indicators (cloudiness and wind anomalies) displayed neutral conditions for most of June.