Category Archives: Fortnightly Weather Outlook

Subseasonal Weather Outlook (16 Jan – 31 Jan 2019)

Issued 26 Jan 2019
valid for weeks 3 and 4: 16 Jan – 31 Jan

 
Under the prevailing Northeast Monsoon condition, weather over the northern ASEAN region is expected to remain dry while scattered rain showers are expected over the southern ASEAN region.

No significant regional-scale rainfall anomaly is expected for most parts of the region, but coastal Viet Nam may experience wetter-than-normal weather in Week 3 due to a strengthening of northeasterly winds. Warmer temperatures experienced in many parts of western Southeast Asia region are expected to ease.

The MJO that has been active in the Pacific Ocean is expected to rapidly weaken by the start of the fortnight. However, it may re-emerge in the Indian Ocean or the western Maritime Continent during Week 4.

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.

Subseasonal Weather Outlook (1 Jan – 15 Jan 2019)

Issued 2 Jan 2019
valid for weeks 1 and 2: 1 Jan – 15 Jan

 
In the first week of the fortnight, a northeast monsoon surge is expected to bring wetter conditions over the South China Sea and over coastal Thailand and Viet Nam. Elsewhere in the Mekong sub-region, cooler conditions can be expected. The stronger monsoonal winds are likely to bring wetter weather to areas around the Java Sea as well. Conversely drier conditions are expected over the Philippines.

By week 2, the wetter conditions over the South China Sea are likely to spread southward to affect the north-eastern coast of Peninsular Malaysia and southern Thailand. Areas around the Java Sea are likely to become drier during the week.

The MJO is currently active in the western Pacific Ocean and is expected to continue propagating eastward. However, the strength and speed of the MJO are uncertain.

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.

Subseasonal Weather Outlook (16 Dec – 31 Dec 2018)

Issued 14 Dec 2018
valid for weeks 3 and 4: 16 Dec – 31 Dec

For the first week of the fortnight, wetter-than-average conditions are forecast over southern Thailand and along coastal Myanmar due to possible tropical cyclone formation over the Bay of Bengal.

Meanwhile, the Madden-Julian Oscillation (MJO) is forecast to propagate eastwards from Phase 3 to Phase 5 and possibly further in the coming fortnight. The MJO, together with a possible Northeast Monsoon surge, is expected to bring above-average rainfall over southern Viet Nam, Cambodia, southern Thailand and northern Peninsular Malaysia in the last week of December.

In the southern ASEAN region, drier-than-average conditions are likely over Java and its surrounding vicinity in the second half of the month.

Above-average temperatures are expected in parts of Thailand, northern Lao PDR, northern Viet Nam and western Cambodia for the second half of December. Elsewhere, temperatures are likely to be near-average.

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.

Subseasonal Weather Outlook (1 Dec – 15 Dec 2018)

Issued 3 Dec 2018
valid for weeks 1 and 2: 1 Dec – 15 Dec

 
The Northeast Monsoon season will bring the traditional dry season to the northern ASEAN region, and more shower activities to the southern ASEAN region.

Drier-than-usual conditions that have persisted over much of the Philippines and northern Borneo are forecast to continue.

There are signs of MJO strengthening in the Pacific Ocean. The MJO is expected to further develop and propagate through Phase 2 in the latter part of fortnight. This may bring more rainfall than average to the equatorial South China Sea region, with the highest likelihood over southern Thailand and northern Peninsular Malaysia towards the second week of December.

Temperatures in the Mekong sub-region are expected to be slightly warmer.

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.

Subseasonal Weather Outlook (16 Nov – 30 Nov 2018)

Issued 14 Nov 2018
valid for weeks 3 and 4: 16 Nov – 30 Nov

Climatologically, the northern ASEAN region experiences drier weather in the second half of November compared to the southern ASEAN region, where there would typically be more shower activities during this period. For the coming fortnight, drier-than-average conditions are expected over parts of Malaysia, Sumatra and Kalimantan. This is particularly so in the first week of the fortnight when the MJO is forecast to propagate eastwards through Phases 5 and 6. However, models’ predictions of the MJO development differ, with some models forecasting a weakening of the MJO during this period.

Slightly warmer temperatures are expected for the Mekong sub-region except for Myanmar. Near normal temperatures are predicted elsewhere.

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.

Subseasonal Weather Outlook (16 Oct – 31 Oct 2018)

Issued 15 Oct 2018
valid for weeks 3 and 4: 16 Oct – 31 Oct

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

From mid-October, wetter conditions may develop over Myanmar, especially over the coastal areas, due to an increase in rain showers that may be brought by tropical cyclones developing over the Bay of Bengal. The drier than normal conditions experienced by much of the Mekong sub-region in the first half of the month are likely to rescind, and a return to normal conditions can be expected for parts of the sub-region. Conditions are likely to be drier than normal in Viet Nam and the Philippines.

For the southern ASEAN region, drier conditions around the Java Sea area, including southern parts of Sumatra and Kalimantan, can be expected.

Warmer temperatures are forecast for the Mekong sub-region, and in Java and southern Sumatra.

The MJO signal is active in Phase 2 and may contribute to the development of tropical lows over the Bay of Bengal and the wet anomaly over coastal Myanmar. Most models predict the weakening of the MJO as it moves into the Maritime Continent.

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.

Subseasonal Weather Outlook (1 Oct – 15 Oct 2018)

Issued 3 Oct 2018
valid for weeks 1 and 2: 1 Oct – 15 Oct

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Prevailing drier conditions are expected to persist over the northern ASEAN region, although the extent and magnitude of the conditions around the South China Sea could be influenced by the presence of typhoons in the surrounding region.

A band of above-average rainfall is predicted to develop around the equator and is expected to persist until the end of the first fortnight in October.

During the outlook period, the drier-than-average conditions surrounding Java are expected to continue. These conditions are in part related to cooler sea surface temperatures in the southeast tropical Indian Ocean.

Slightly warmer temperatures are expected over the northern and central ASEAN region, including Thailand, parts of Laos and Vietnam, Cambodia, Malaysia, and the southern Philippines.

An MJO signal has developed in Phase 8. The MJO is expected to strengthen and propagate eastward during the first fortnight of October and contribute to the above-average rainfall around the equator.

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.

Subseasonal Weather Outlook (16 Sep – 30 Sep 2018)

Issued 14 Sep 2018
valid for weeks 3 and 4: 16 Sep – 30 Sep 2018

In the second half of September 2018, wet weather conditions and above-average rainfall are expected in the region around 10⁰ N in the third week of the month. This region is likely to return to normal conditions in the last week of September with the weakening of the Southwest Monsoon winds. For most of the southern ASEAN region, slightly drier conditions are expected.

No significant regional temperature anomalies are expected during the second half of September 2018.

No significant MJO signal is currently present. Most models predict no coherent MJO to develop during the second half of September.

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.

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.

Subseasonal Weather Outlook (1 Aug – 15 Aug 2018)

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

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 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.

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.