Monthly Archives: August 2022

1.1 During July 2022, most of the southeastern Maritime Continent region and central/eastern parts of Mainland Southeast Asia experienced above-average rainfall (Figure 1). The largest positive anomalies (wetter conditions) were recorded over the southern coastal parts of Mainland Southeast Asia, eastern Sulawesi, western Papua, and the Maluku Islands based on both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). In contrast, most of the northern/central Philippines recorded below-average rainfall. The rest of regions either experienced near-average rainfall for this time of year, or a mix between above- and below-average. The two datasets agree well over most of the ASEAN region. However, there are some discrepancies over the western parts of Peninsular Malaysia where GSMaP-NRT recorded near-average rainfall whereas CMORPH-Blended recorded below-average rainfall, and over southern Sumatra where GSMaP-NRT recorded near- to above-average rainfall whereas CMORPH-Blended recorded near-average rainfall.

1.2 The observed rainfall anomaly pattern of above-average rainfall for southeastern Maritime Continent region and central/eastern parts of the Mainland Southeast Asia is broadly consistent with the predictions from the subseasonal weather outlooks for July 2022 (27 June – 10 July, 11 – 24 July and 25 July – 7 August).

Figure 1: Rainfall anomalies for July 2022 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2021. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 Much of the ASEAN region experienced above-average temperatures during July 2022 (Figure 2). The warmest anomalies were recorded over western/northern Myanmar and northern Lao PDR, followed by northern Viet Nam, Peninsular Malaysia, parts of the Philippines, and southeastern parts of the Maritime Continent. Elsewhere, near-average temperatures were generally recorded.

 

Figure 2: Temperature anomalies for July 2022 based on ERA-5 reanalysis. The climatological reference period is 2001-2021. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 A Madden-Julian Oscillation (MJO) signal was present mostly over eastern Indian Ocean (Phase 3) and the Maritime Continent (Phases 4 and 5) in the first week of July 2022, based on the MJO phase diagram below (Figure 3). In the second and third week of July, the MJO signal weakened and became indiscernible. This signal then re-emerged over the Western Hemisphere (Phase 1) towards the end of the third week, propagated eastwards and weakened over the western Indian Ocean (Phase 2) in the last week of July. 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 July. Also for July, Phase 4 bring wetter conditions in northern Southeast Asia while Phase 5 bring wetter conditions to the southeastern Maritime Continent. Therefore, the MJO may have contributed to the drier conditions over northern half of the Philippines, and wetter conditions over southern coastal parts of Mainland Southeast Asia and southeastern Maritime Continent region in July.

 

Figure 3: The MJO phase diagram. The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator (denoted in the text with the first day of the month in blue and the last day of the month in red). The distance of the index from the centre of the diagram is related to the strength of the MJO. Values within the grey circle are considered weak or indiscernible (data from the Bureau of Meteorology, Australia).

 

2.2 Over the tropical Pacific Ocean, weak La Niña conditions were present for much of July 2022. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean remain consistent with weakening La Niña conditions. 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 continuing signs of a developing negative Indian Ocean Dipole (IOD) in July. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.