Subseasonal Weather Outlook and Review

1.1 In the second fortnight of May 2019, prevailing winds were mostly from the southwest or west over the northern ASEAN region. In the southern ASEAN region, winds were generally weak and variable in direction over the equatorial region, but moderate to strong south-easterly winds prevailed over the Java Sea and Banda Sea areas.

1.2 In the second half of May 2019, there were shower activities on most days over many parts of the ASEAN region except over the Java Sea area where dry weather prevailed. This was brought about by the incursion of dry continental air mass from Australia, transported by the anomalously strong south-easterly winds over the Java Sea during the review period. Below-average rainfall was also observed in southern Sumatra, parts of Kalimantan, northern Myanmar and eastern Thailand.

1.3 The Madden-Julian Oscillation (MJO) propagated through Phases 8 – 1, and this could have contributed to the drier-than-average conditions over the Java Sea area. The MJO contributed to large-scale wind anomalies over the Indian Ocean and the Java Sea. Toward the end of May, the MJO reached the Indian Ocean (Phase 2).

1.4 Slightly warm sea-surface temperature (SST) anomalies over the Nino3.4 region were still observed. There was a slight weakening of the trade winds in the eastern Pacific Ocean towards the end of May 2019. Overall, there were no clear indications of El Nino conditions as the coupling of the SST and atmosphere over the tropical Pacific remained inconsistent.

Figure 4: The MJO phase diagram for April 2019-May 2019 (green for May). The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)

1.1 In the second fortnight of May 2019, prevailing winds were mostly from the southwest or west over the northern ASEAN region. In the southern ASEAN region, winds were generally weak and variable in direction over the equatorial region, but moderate to strong south-easterly winds prevailed over the Java Sea and Banda Sea areas.

1.2 In the second half of May 2019, there were shower activities on most days over many parts of the ASEAN region except over the Java Sea area where dry weather prevailed. This was brought about by the incursion of dry continental air mass from Australia, transported by the anomalously strong south-easterly winds over the Java Sea during the review period. Below-average rainfall was also observed in southern Sumatra, parts of Kalimantan, northern Myanmar and eastern Thailand.

1.3 The Madden-Julian Oscillation (MJO) propagated through Phases 8 – 1, and this could have contributed to the drier-than-average conditions over the Java Sea area. The MJO contributed to large-scale wind anomalies over the Indian Ocean and the Java Sea. Toward the end of May, the MJO reached the Indian Ocean (Phase 2).

1.4 Slightly warm sea-surface temperature (SST) anomalies over the Nino3.4 region were still observed. There was a slight weakening of the trade winds in the eastern Pacific Ocean towards the end of May 2019. Overall, there were no clear indications of El Nino conditions as the coupling of the SST and atmosphere over the tropical Pacific remained inconsistent.

Figure 4: The MJO phase diagram for April 2019-May 2019 (green for May). The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator. The distance of the index from the centre of the diagram is correlated with the strength of MJO. When the index falls within the circle, the MJO is considered weak or indiscernible. (Source: Bureau of Meteorology)