Subseasonal Weather Outlook and Review

1.1 Northeast Monsoon conditions began to set in over the northern ASEAN region in mid November. Persistent north-easterly winds prevailed over the northern ASEAN region and the South China Sea. Winds to the south of the equator were light and blew mainly from the southeast.

Figure 1: 5000 ft average winds (left) and winds anomaly (right) for 16 – 30 November 2019. (Source: JMA)

1.2 Most of the rainfall fell over the equatorial region, including Brunei, Malaysia, Singapore, Sumatra and Kalimantan. Typhoon Kalmaegi, which developed over the sea areas east of the Philippines, brought heavy showers to the northern parts of Luzon between 18 – 20 November 2019. Dry weather prevailed over most parts of the Mekong sub-region during the review period.

Figure 2: Historical track of Typhoon Kalmaegi. (Source: JAXA)

1.3 Because of the dry weather in the northern ASEAN region, many parts of the Mekong sub-region experienced below-average rainfall during the review period. In the southern ASEAN region, rainfall was near-average to above-average over the equatorial region. Rainfall was below-average over the eastern archipelago of Indonesia.

Figure 3: Daily average rainfall for the ASEAN region in the second fortnight of November 2019. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 4: Percent of average rainfall for 16 – 30 November 2019. The rainfall data is less representative for areas with a less dense rainfall network. Hatched areas indicate climatology dry mask (average daily rainfall below 1 mm). (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.4 In the second half of November 2019, the Madden-Julian Oscillation (MJO) began to weaken but continued to propagate through Phase 8 – 1 into the Indian Ocean. The MJO although weak, could have contributed to the easterly wind anomalies observed over the Indian Ocean and Java Sea.

Figure 5: The MJO phase diagram for November 2019 (blue). 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)

1.5 The El-Niño Southern Oscillation (ENSO) continued to remain in the neutral state (i.e neither El Niño nor La Niña conditions). The Indian Ocean Dipole (IOD) remained in the positive phase, but was declining.

1.1 Northeast Monsoon conditions began to set in over the northern ASEAN region in mid November. Persistent north-easterly winds prevailed over the northern ASEAN region and the South China Sea. Winds to the south of the equator were light and blew mainly from the southeast.

Figure 1: 5000 ft average winds (left) and winds anomaly (right) for 16 – 30 November 2019. (Source: JMA)

1.2 Most of the rainfall fell over the equatorial region, including Brunei, Malaysia, Singapore, Sumatra and Kalimantan. Typhoon Kalmaegi, which developed over the sea areas east of the Philippines, brought heavy showers to the northern parts of Luzon between 18 – 20 November 2019. Dry weather prevailed over most parts of the Mekong sub-region during the review period.

Figure 2: Historical track of Typhoon Kalmaegi. (Source: JAXA)

1.3 Because of the dry weather in the northern ASEAN region, many parts of the Mekong sub-region experienced below-average rainfall during the review period. In the southern ASEAN region, rainfall was near-average to above-average over the equatorial region. Rainfall was below-average over the eastern archipelago of Indonesia.

Figure 3: Daily average rainfall for the ASEAN region in the second fortnight of November 2019. (Source: JAXA Global Satellite Mapping of Precipitation)

Figure 4: Percent of average rainfall for 16 – 30 November 2019. The rainfall data is less representative for areas with a less dense rainfall network. Hatched areas indicate climatology dry mask (average daily rainfall below 1 mm). (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.4 In the second half of November 2019, the Madden-Julian Oscillation (MJO) began to weaken but continued to propagate through Phase 8 – 1 into the Indian Ocean. The MJO although weak, could have contributed to the easterly wind anomalies observed over the Indian Ocean and Java Sea.

Figure 5: The MJO phase diagram for November 2019 (blue). 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)

1.5 The El-Niño Southern Oscillation (ENSO) continued to remain in the neutral state (i.e neither El Niño nor La Niña conditions). The Indian Ocean Dipole (IOD) remained in the positive phase, but was declining.