Monthly Archives: August 2018

August 30, 2018

Subseasonal Weather Outlook (1 Sep – 15 Sep 2018)

Issued 30 Aug 2018
valid for weeks 1 and 2: 1 Sep – 15 Sep 2018

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

The traditional rainy season over the northern ASEAN region is forecast to persist in the first fortnight of September 2018. During this period there is expected to be less rainfall than average in the region around 10°N, particularly towards the end of the first week. Along with the drier conditions, warmer temperatures are also expected inland areas of northern Southeast Asia.

In the southern ASEAN region, rainfall and temperatures are generally expected to be near-average, but areas along the equatorial belt may experience slightly wetter conditions in the first fortnight of September.

Some models forecast the MJO to re-emerge in the ASEAN region during this outlook period, and this may lower the likelihood of drier conditions in the northern ASEAN region.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

Outlook for Land Fires and Smoke Haze Situation (1 – 15 Sep 2018)

Outlook for Land Fires and Smoke Haze Situation (1- 15 Sep 2018)

Issued 30 Aug 2018

No significant hotspot activities are expected in the northern ASEAN region due to the rainy weather. In the southern ASEAN region, brief periods of drier weather could lead to increased hotspot activities, particularly in southern Sumatra and some parts of Kalimantan, and increase the risk of transboundary haze occurrence in the region.

August 17, 2018

Review of Land Fires and Smoke Haze Situation for Second Fortnight of July 2018

1.1 In the northern ASEAN region, no significant hotspot activities were observed.

1.2 In mid-July, drier weather in the southern ASEAN region contributed to an increase in hotspot activities, particularly in northern Riau and West Kalimantan. Smoke haze from hotspots in northern Riau was observed to spread northward across the Strait of Malacca towards Peninsular Malaysia. Several clusters of hotspots with smoke plumes were also observed in West Kalimantan and western Sarawak. These hotspots were short-lived and shower activities toward the end of July 2018 helped to subdue the hotspot activities there.

1.3 Figures below show satellite images over the ASEAN region in the second fortnight of July 2018.

Figure 1: Smoke plumes from hotspot in northern Riau (marked by red dotted lines) that were blown across the Strait of Malacca

Figure 2: Smoke plumes (marked by red dotted lines) observed around hotspot clusters detected in Kalimantan and Sarawak

Review of Regional Weather Conditions for Second Fortnight of July 2018

Print Version

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

1.1 Southwest Monsoon conditions continued to prevail in the second fortnight of July 2018. The monsoonal rain band brought rainy weather to many parts of the northern ASEAN region. In general, there was above normal rainfall, except for southern Thailand and southern Viet Nam, where rainfall was below normal. In contrast, dry weather prevailed over the southern ASEAN region. Rainfall was below normal in southern Sumatra, southern Kalimantan, Sabah and Java. Nonetheless, there was a gradual increase in shower activities towards the end of July.

1.2 The daily average rainfall and the percent of normal rainfall for the second fortnight of July 2018 are shown in Figure 1 and Figure 2.

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

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

1.3 On 17 July 2018, Tropical Storm Son-Tinh developed over the South China Sea and tracked westwards before making landfall at northern Viet Nam on 19 July 2018. The tropical storm brought torrential rain to parts of Viet Nam and Lao PDR. The track of Tropical Storm Son-Tinh from 17 July 2018 to 19 July 2018 is shown in Figure 3.

Figure 3 Track for Tropical Storm Son-Tinh (17 – 19 July 2018)

1.4 Broad scale anomalous westerly winds were observed over the northern ASEAN region, brought about by the development of tropical low pressure systems over the South China Sea. Meanwhile, the winds over the southern ASEAN region were predominantly from the southeast or southwest.

figure3b

Figure 4: 5000 ft average winds (left) and anomaly (right) for 16 – 31 July 2018. (Source: JMA)

1.5 Neutral conditions of the El Niño-Southern Oscillation (ENSO) persisted, and the sea surface temperature over the tropical Pacific Ocean decreased slightly but continued to remain higher than average. Other atmospheric indicators were also indicative of neutral conditions.

1.6 The Madden Julian Oscillation (MJO) transitioned from Phase 5 to Phase 6 in the third week of July. The MJO subsequently weakened and became indiscernible by the end of July. MJO Phases 5 and 6 typically brought wetter weather over the Western Pacific Ocean and drier weather over the surrounding region of Java Sea. This was consistent with the regional rainfall patterns observed.

Figure 5: The MJO phase diagram for June-July-August 2018 (green for July). 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)

August 13, 2018

Alert20180813 – Activation of Alert Level 2 for the southern ASEAN region

Activation of Alert Level 2 for the southern ASEAN region

Dry weather over the weekend has led to some deterioration of the haze situation in Sumatra and Kalimantan. The latest daytime satellite images show slight to moderate smoke haze from clusters of hotspots over peatlands in northern Riau being blown by the prevailing southwesterly winds toward the Strait of Malacca. In West Kalimantan, moderate to dense smoke haze from persistent hotspots has been observed, and the prevailing winds could blow the haze toward western Sarawak. In central Sarawak, smoke plumes could also be observed in the vicinity of hotspots.

Based on surveillance by the NOAA-19 satellite, 29 hotspots were detected on 11 August 2018 and 62 on 12 August 2018 in Sumatra. In Kalimantan, 2 hotspots were detected on 11 August 2018 and 3 on 12 August 2018 (the low hotspot count on both days was due to a partial satellite pass). There has also been a deterioration in the air quality in parts of Kalimantan and visibility in Pontianak has been reduced to 4 km due to haze conditions since this morning.

In the next several days, the prevailing dry weather and winds are expected to persist over Sumatra and Borneo. Notwithstanding the current relatively low hotspot count in Sumatra and Kalimantan, the expected dry weather and wind conditions could lead to the occurrence of transboundary smoke haze in some parts of the region.

August 2, 2018

Outlook for Land Fires and Smoke Haze Situation (1 – 15 Aug 2018)

Issued 2 Aug 2018

The prevailing wet weather in the northern ASEAN region is likely to keep hotspot activities subdued. In the southern ASEAN region, a return of dry conditions in areas such as Kalimantan may contribute to an increase in hotspot activities.

Subseasonal Weather Outlook (1 Aug – 15 Aug 2018)

Issued 2 Aug 2018
valid for weeks 1 and 2: 1 Aug – 15 Aug 2018

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wet weather can be expected to prevail in most parts of the northern ASEAN region, with wetter conditions forecast for the first week.

In the southern ASEAN region, drier weather conditions with below average rainfall can be expected over Kalimantan, Sulawesi, Java and the Lesser Sunda Islands during the first fortnight of the month. For the rest of the southern ASEAN region, no significant wet or dry conditions are likely, and rainfall is forecast to be near-average (as in Figure 1).

With no significant regional temperature features expected in the first half of August 2018, temperatures are likely to be near-normal (as in Figure 2).
The MJO currently over the western Pacific Ocean is forecast to weaken over the coming days and re-emerging around mid-August. This is expected to influence the rainfall patterns in the Southeast Asia region.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.