Monthly Archives: July 2018

July 31, 2018

Alert20180731 – Downgrade of Alert Level 2 to Alert Level 1 for the southern ASEAN region

Downgrade of Alert Level from 2 to 1 for the southern ASEAN region

In recent days, increased shower activities have helped to subdue hotspot activities in Sumatra and Kalimantan. Based on surveillance by the NOAA-19 satellite, 6 and 0 hotspots were detected in Sumatra, and 9 and 10 hotspots were detected in Kalimantan on 29 and 30 July 2018 respectively. No significant smoke haze was observed in the region.

In the next two weeks, shower activities are forecast for most parts of the southern ASEAN region, and this will help subdue hotspot activities in the region

July 25, 2018

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

1.1 During the review period, hotspot activities in the northern ASEAN region remained subdued due to the prevailing wet weather conditions.

1.2 In the southern ASEAN region, there were increased hotspot activities observed in Sarawak and West Kalimantan in the latter half of the fortnight, as dry weather conditions set in over the region. Smoke plumes were observed emanating from some of the hotspots.

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

Figure 1: Himawari-8 satellite image on 8 Jul 2018 shows hotspot activities in the northern ASEAN region subdued by wet weather conditions.

Figure 2: NOAA-19 satellite image on 14 Jul 2018 shows isolated hotspots and smoke plumes detected in Sarawak and West Kalimantan.

Review of Regional Weather Conditions for First Fortnight of July 2018

Print Version

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

1.1 The Southwest Monsoon conditions prevailed in the first fortnight of July 2018. During the period, the equatorial region received more rainfall than the other parts of the Southeast Asia in the first week of July. In the second week of the month, with the strengthening of the monsoon winds and movement of the monsoon rain band away from the equatorial region, wetter weather was felt in the northern ASEAN region while the southern ASEAN region transitioned from wet to dry weather conditions by the end of the fortnight. These conditions were consistent with model forecasts, as indicated in the subseasonal outlook for 2 – 16 July 2018.

1.2 During the review period, parts of the Mekong sub-region, including Myanmar, Lao PDR and Viet Nam, received above-normal rainfall. Rainfall was below normal over most parts of the western equatorial Maritime Continent, particularly over Peninsular Malaysia, Sumatra, Java, and West and Central Kalimantan. The rainfall distribution and the percent of normal rainfall for the first fortnight of July 2018 are shown in Figures 1 and 2.

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

Figure 2: Percentage of Normal Rainfall for 1 – 15 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 Stronger-than-usual southwesterly winds prevailed over the northern ASEAN region and the South China Sea. In areas south of the Equator, winds generally blew from the southeast or south, typical of the wind flow for this time of the year. Figure 3 shows the average and anomalous winds at 5000 feet.

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Figure 3: 5000 ft average winds (left) and anomaly (right) for 1 – 15 July 2018. (Source: JMA)

1.4 The El Niño-Southern Oscillation (ENSO) remained in the neutral state (neither El Niño nor La Niña). While there were signs of further increase in sea surface temperatures in the eastern Pacific Ocean, other atmospheric indicators continued to show neutral conditions.

1.5 In the second week of July 2018, the Madden Julian Oscillation (MJO) strengthened and progressed through Phases 4 and 5 . While its strength was stronger than expected, its movement was largely in line with model forecasts. This was consistent with the increased rainfall activities and a strengthening of south-westerly or westerly winds observed over the northern ASEAN region, and the transition from wet to dry conditions over the southern ASEAN region.

Figure 4: The MJO phase diagram for June-July 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).

July 17, 2018

Outlook for Land Fires and Smoke Haze Situation (16 – 31 Jul 2018)

Issued 17 Jul 2018

Hotspot activities in the northern ASEAN region are expected to remain subdued due to the prevailing wet weather conditions. In the southern ASEAN region, with dry conditions forecast to persist for the rest of the month, there is an increased risk of hotspot activities in the region, in particular in southern Sumatra, western and central Kalimantan. Further escalation of hotspot activities could lead to the occurrence of transboundary smoke haze.

Subseasonal Weather Outlook (16 Jul – 31 Jul 2018)

Issued 17 Jul 2018
valid for weeks 3 and 4: 16 Jul – 31 Jul 2018

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Above-average rainfall is expected for the northern ASEAN region. Towards the end of the fortnight, a return to average conditions can be expected, initially over the southern areas and gradually moving northwards to affect all parts of the region.

For the southern ASEAN region, prevailing dry conditions are expected to persist for the rest of the month.

As a result of the dry conditions, temperatures in the southern ASEAN region are expected to be warm, in particular over the inland areas. Below-average temperatures are expected in the eastern part of Mekong sub-region.

There are indications of an MJO developing over the Maritime Continent (Phase 4) and is forecast to move slowly eastwards (Phases 5 and 6), which is consistent with the rainfall and temperature outlooks.

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.

Alert20180717 – Activation of Alert Level 2 for the southern ASEAN region

Activation of Alert Level 2 for the southern ASEAN region

Increased hotspot activities were observed in Kalimantan and Sumatra recently due to drier weather prevailing over the region last week. Isolated hotspots and localised smoke plumes were detected in Sarawak, West, Central and South Kalimantan in the past few days. In Sumatra, a cluster of hotspots was observed in northern Riau. The smoke plumes were being blown northward by the prevailing winds over the Strait of Malacca. Based on surveillance by the NOAA-19 satellite, 6 and 12 hotspots were detected in Sumatra, and 11 and 1 hotspots were detected in Sarawak and Kalimantan on 15 and 16 July 2018 respectively.

Dry weather conditions are expected to persist for most parts of the southern ASEAN region in the coming weeks, and this could lead to further escalation of hotspot activities in the fire-prone areas.

July 12, 2018

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

1.1 During the review period, there were isolated hotspots detected in the ASEAN region, but the overall hotspot activities were generally subdued due to the wet weather.

1.2 During the brief periods of drier weather, there were a few hotspots with thin smoke plumes observed on one or two days in central Sumatra. However, the smoke plumes were localised and short-lived.

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

Figure 1: Himawari-8 satellite image on 16 Jun 2018 shows a thin smoke plume over central Sumatra.

Figure 2: Himawari-8 satellite image on 29 Jun 2018 shows wet weather prevailed over most parts of the region.

Review of Regional Weather Conditions for Second Fortnight of June 2018

Print Version

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

1.1 The southwest monsoon conditions prevailed in the second fortnight of June 2018. Shower activities were observed over many parts of the region.

1.2 During this period, there were isolated showers over parts of the northern ASEAN region but wetter weather was observed over coastal areas of Myanmar. In southern Myanmar, heavy rains reportedly triggered floods and landslides during the beginning of the second fortnight. Based on climatology, the wet conditions over coastal Myanmar is typical during this period of the season. Most parts of the Mekong sub-region experienced below-normal to near-normal rainfall, while northern and coastal areas of Myanmar, eastern Cambodia and southern Vietnam received above-normal rainfall.

1.3 In the southern ASEAN region, large scale convergence of winds caused by a circulation west of Borneo brought widespread shower activities over the region. Most areas experienced wetter than usual conditions, except for central Sumatra, central Kalimantan and Java where below-normal rainfall were received.

1.4 The rainfall distribution and the percentage of normal rainfall for the second fortnight of June 2018 are shown in Figures 1 and 2.

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

Figure 2: Percentage of Normal Rainfall for 15 – 30 June 2018. The rainfall data may be less representative for areas with a less dense rainfall network. (Source: IRI NOAA/NCEP CPC Unified Precipitation Analyses)

1.5 During the second fortnight of June 2018, weather in the region was influenced by Tropical Storm “Gaemi” and Typhoon “Prapiroon” as well. Rainbands associated with “Gaemi” brought widespread showers over parts of the northern ASEAN region, and persistent wet weather over Sumatra, Peninsular Malaysia and Singapore in the southern ASEAN region. Toward the end of June 2018, rain bands from “Prapiroon” also brought widespread showers over most parts of the ASEAN region.

Figure 3: Historical storm track for Tropical Storm Gaemi and Typhoon Prapiroon. (Source: JAXA)

1.6 Prevailing winds over the northern ASEAN region and the South China Sea were weaker than usual and blew predominantly from the southwest or west. Over the southern ASEAN region, easterly to southeasterly winds prevailed. Figure 4 shows the average and anomalous winds at 5000 feet.

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Figure 4: 5000 ft average winds (left) and anomaly (right) for 15 – 30 June 2018. (Source: JMA)

1.7 The El Niño-Southern Oscillation (ENSO) remained in the neutral state (neither El Niño nor La Niña). The atmospheric and oceanic indicators of ENSO such as sea surface temperature and trade winds were also indicative of neutral conditions, although the sea surface temperatures in the eastern Pacific Ocean have been observed to be warming slowly.

1.8 The Madden Julian Oscillation (MJO) progressed from Phase 1 to Phase 2 before the signal weakened toward the end of the month. Typically, the MJO in Phases 1 and 2 brings less rainfall over the coastal Myanmar region and the South China Sea, and the MJO in Phase 2 would bring slightly enhanced rainfall around Sumatra and Borneo. In the second fortnight of June 2018, an increase in rainfall was observed along the belt between the Equator and 5°S.

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

July 5, 2018

ASMC Bulletin (Issue #1, Feb 2018)

Subseasonal Weather Outlook (2 Jul – 16 Jul 2018)

Issued 5 Jul 2018
valid for weeks 1 and 2: 2 Jul – 16 Jul 2018

The Madden-Julian Oscillation (MJO) is currently weak but active over the western Indian Ocean. Over the first two weeks of July 2018, some models predict the eastward propagation of the weak MJO while other models project the MJO to become indiscernible as it moves over the Maritime Continent. Thus for the first fortnight of July 2018, the MJO is not expected to have a large impact on the region.

In terms of the weekly rainfall for the Southeast Asia region, the eastern Maritime Continent can expect above-average rainfall in the first week of July 2018. However, as the second week approaches, the wet weather conditions in the southern ASEAN region is expected to gradually ease due to a northward shift of the rain band associated with the strengthening of monsoon winds. Drier weather conditions can be expected over most parts of the southern ASEAN region in the second week of July.

In the northern ASEAN region, rainfall is expected to be above-average rainfall in the second week of July 2018, associated with a strengthening of mid-level westerly winds in the region. Areas around the Philippines, coasts of the Mekong sub-region and parts of the South China Sea have a higher likelihood of receiving above-average rainfall.

During this two-week period, the temperature over much of Southeast Asia is expected to be near-average. In parts of the Mekong sub-region, warmer temperatures are expected in week 1 than in week 2 where a gradually return to average conditions is expected.

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.