Subseasonal Weather Outlook and Review

1.1 In the first fortnight of July 2019, moderate to strong southwesterly or westerly winds prevailed over the northern ASEAN region. In particular, anomalously strong southwesterly winds were observed to the east of Viet Nam during the first half of the fortnight under the influence of Tropical Storm Mun (Figure 2). In the southern ASEAN region, the prevailing winds blew mainly from the southeast or southwest, with wind anomalies observed west of Sumatra. Figure 1 shows the average and anomalous winds at 5000 feet.

Figure 2: Track for Tropical Storm Mun (2-4 Jul 2019).

1.2 Southwest Monsoon conditions prevailed in the first half of July 2019. Much of the northern ASEAN region received above-average rainfall except for northern Philippines and Thailand. In the southern ASEAN region, below-average rainfall was observed over many areas (Figures 3 and 4).

1.3 Throughout the first fortnight of July 2019, the Madden-Julian Oscillation (MJO) was in the Western Hemisphere and Africa, and it did not significantly influence the weather over the ASEAN region (Figure 5).

Figure 5: The MJO phase diagram for Jul 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)

1.4 The state of the El Niño-Southern Oscillation (ENSO) is currently neutral (neither El Niño nor La Niña). While the sea-surface temperature (SST) anomalies were slightly above average across the tropical Pacific Ocean Nino 3.4 region, other atmospheric indicators continued to show neutral conditions.

1.1 In the first fortnight of July 2019, moderate to strong southwesterly or westerly winds prevailed over the northern ASEAN region. In particular, anomalously strong southwesterly winds were observed to the east of Viet Nam during the first half of the fortnight under the influence of Tropical Storm Mun (Figure 2). In the southern ASEAN region, the prevailing winds blew mainly from the southeast or southwest, with wind anomalies observed west of Sumatra. Figure 1 shows the average and anomalous winds at 5000 feet.

Figure 2: Track for Tropical Storm Mun (2-4 Jul 2019).

1.2 Southwest Monsoon conditions prevailed in the first half of July 2019. Much of the northern ASEAN region received above-average rainfall except for northern Philippines and Thailand. In the southern ASEAN region, below-average rainfall was observed over many areas (Figures 3 and 4).

1.3 Throughout the first fortnight of July 2019, the Madden-Julian Oscillation (MJO) was in the Western Hemisphere and Africa, and it did not significantly influence the weather over the ASEAN region (Figure 5).

Figure 5: The MJO phase diagram for Jul 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)

1.4 The state of the El Niño-Southern Oscillation (ENSO) is currently neutral (neither El Niño nor La Niña). While the sea-surface temperature (SST) anomalies were slightly above average across the tropical Pacific Ocean Nino 3.4 region, other atmospheric indicators continued to show neutral conditions.