Review of Regional Weather Conditions for Second Fortnight of August 2018

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1. Review of Regional Weather Conditions for Second Fortnight of August 2018

1.1 Southwest Monsoon conditions prevailed in the second fortnight of August 2018. During the period, rainy weather persisted over most parts of the northern ASEAN region. For the northern parts of Myanmar, Lao PDR and Vietnam and parts of the Philippines, above-average rainfall was recorded.

1.2 In the southern ASEAN region, Sumatra and Kalimantan experienced drier conditions during the first half of the fortnight. This was followed by a gradual increase of shower activities in the latter half of the fortnight. The Java region remained generally dry throughout the period.

1.3 The daily average rainfall and the percentage normal of rainfall for the second fortnight of August 2018 are shown in Figure 1 and Figure 2.

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Figure 1: Daily average rainfall for the ASEAN region in the second fortnight of August 2018. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 2: Percentage of Normal Rainfall for 16 – 31 August 2018. The rainfall data may be less representative for areas with a less dense rainfall network. (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.4 Stronger-than-usual southwesterly winds prevailed over the northern ASEAN region. In the southern ASEAN region, there were no significant wind anomalies observed, and the prevailing winds generally blew from the southeast or southwest. Figure 3 shows the average and anomalous winds at 5000 feet.

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Figure 3: 5000 ft average winds (left) and anomalies (right) for 16 – 31 August 2018. (Source: JMA)

1.6 The El-Southern Oscillation (ENSO) remained in the neutral state(neither El Niño nor La Niña), and other atmospheric indicators continued to show neutral conditions.

1.7 The Madden Julian Oscillation (MJO), which started in Phase 6, weakened and became non-discernible throughout the review period. The weakening of the MJO Phase 6 partly contributed to the cessation of drier conditions over the southern ASEAN region in the second fortnight of August 2018.

Figure 4: The MJO phase diagram for August 2018 (green for August). 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)