Review of Regional Weather for June 2022
1.1 During June 2022, below-average rainfall was recorded over northeast Maritime Continent and coastal parts of southern Mainland Southeast Asia, while near- to above-average rainfall was recorded elsewhere (Figure 1). The largest positive anomalies in rainfall (wetter conditions) were recorded over northern Myanmar, while the largest negative anomalies in rainfall (drier conditions) was recorded over southern Myanmar and Papua for both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). The two datasets agree well over most of the ASEAN region. However, there are some discrepancies over western coast of Myanmar where GSMaP-NRT recorded below-average rainfall whereas CMORPH-Blended recorded near- to above-average rainfall, and over Cambodia where GSMaP-NRT recorded near- to above-average rainfall whereas CMORPH-Blended recorded below- to near- average rainfall.
1.2 The observed rainfall anomaly pattern of above-average rainfall for parts of the Maritime Continent and below-average rainfall for southern Mainland Southeast Asia is broadly consistent with the predictions from the subseasonal weather outlooks for June 2022 (30 May – 12 June and 13 – 26 June).
1.3 The western Maritime Continent recorded below-average temperature, while the southeastern Maritime Continent and eastern Mainland Southeast Asia recorded above-average temperature in June 2022 (Figure 2). The largest positive anomalies (more than 1°C warmer than normal conditions for June) were over Papua and northern Viet Nam.
2. Climate Drivers
2.1 A Madden-Julian Oscillation (MJO) signal was present mostly over the Western Hemisphere (Phases 8 and 1) and the Indian Ocean (Phases 2 and 3) in June 2022 based on the MJO phase diagram below (Figure 3). In the first week of June, the MJO signal propagated eastward over the Western Hemisphere (from Phase 8 to Phase 1). For the second and third week of May, the MJO signal weakened and remained relatively stationary over the Western Hemisphere (Phase 1), with also the influence from other tropical waves. This signal then strengthened again and propagated rapidly eastwards over the Indian Ocean (Phase 2 and 3) in the last week of June. Typically, Phases 1 and 2 bring drier conditions in northern Southeast Asia while Phases 2 and 3 tend to bring wetter conditions to the western Maritime Continent in June. Therefore, the MJO may have contributed to the drier conditions over southern Mainland Southeast Asia and wetter conditions over the western Maritime Continent in June.
2.2 Over the tropical Pacific Ocean, La Niña conditions were present but show signs of weakening. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean were weakening, indicating weak La Niña conditions in June. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the June to August period. Over the Indian Ocean, there were signs of negative Indian Ocean Dipole development as the Dipole Mode Index (DMI), which is used to measure the Indian Ocean Dipole (IOD) signal, became increasingly negative and had transited into the negative phase in June. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.