Monthly Archives: July 2022

July 22, 2022

Subseasonal Weather Outlook (25 July – 7 August 2022)

Issued: 22 July 2022
First forecast week: 25 July – 31 July
Second forecast week: 1 August – 7 August

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over most of the equatorial ASEAN region in the next fortnight (25 July – 7 August). The highest likelihood of wetter conditions are predicted over the western Maritime Continent and the central parts of equatorial region in Week 1 (25 – 31 July), and over the central-eastern parts of equatorial region in Week 2 (1 – 7 August).

Drier conditions are expected over Mainland Southeast Asia in Week 1 (25 – 31 July). These drier conditions are expected to ease in Week 2 (1 – 7 August), apart from over southern half of Myanmar.

Warmer than usual temperatures are expected over the northern half of Mainland Southeast Asia in the next fortnight (25 July – 7 August).

By the second week of July, the Madden-Julian Oscillation (MJO) signal had decayed over the eastern Maritime Continent (Phase 5) and became indiscernible based on the RMM index. Most models predict the MJO signal to emerge over the Western Hemisphere and Africa (Phase 1) during the start of the forecast period, and to propagate eastwards over the Indian Ocean (Phase 2) by Week 1.

The outlook is assessed for the region in general, where conditions are relative to the average conditions for the corresponding time of year. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

July 14, 2022

Review of Regional Weather for June 2022

1. Overview

1.1 During June 2022, below-average rainfall was recorded over northeast Maritime Continent and coastal parts of southern Mainland Southeast Asia, while near- to above-average rainfall was recorded elsewhere (Figure 1). The largest positive anomalies in rainfall (wetter conditions) were recorded over northern Myanmar, while the largest negative anomalies in rainfall (drier conditions) was recorded over southern Myanmar and Papua for both satellite-derived rainfall estimates datasets (GSMaP-NRT and CMORPH-Blended). The two datasets agree well over most of the ASEAN region. However, there are some discrepancies over western coast of Myanmar where GSMaP-NRT recorded below-average rainfall whereas CMORPH-Blended recorded near- to above-average rainfall, and over Cambodia where GSMaP-NRT recorded near- to above-average rainfall whereas CMORPH-Blended recorded below- to near- average rainfall.

1.2 The observed rainfall anomaly pattern of above-average rainfall for parts of the Maritime Continent and below-average rainfall for southern Mainland Southeast Asia is broadly consistent with the predictions from the subseasonal weather outlooks for June 2022 (30 May – 12 June and 13 – 26 June).

Figure 1: Rainfall anomalies for the month of June 2022 based on GSMaP-NRT data (left) and CMORPH-Blended data (right). The climatological reference period is 2001-2021. Green colour denotes above-average rainfall (wetter), while orange denotes below-average rainfall (drier).

1.3 The western Maritime Continent recorded below-average temperature, while the southeastern Maritime Continent and eastern Mainland Southeast Asia recorded above-average temperature in June 2022 (Figure 2). The largest positive anomalies (more than 1°C warmer than normal conditions for June) were over Papua and northern Viet Nam.

Figure 2: Temperature anomalies for the month of June 2022 based on ERA-5 reanalysis. The climatological reference period is 2001-2021. Red colour denotes above-average temperature (warmer), while blue denotes below-average temperature (colder).

2. Climate Drivers

2.1 A Madden-Julian Oscillation (MJO) signal was present mostly over the Western Hemisphere (Phases 8 and 1) and the Indian Ocean (Phases 2 and 3) in June 2022 based on the MJO phase diagram below (Figure 3). In the first week of June, the MJO signal propagated eastward over the Western Hemisphere (from Phase 8 to Phase 1). For the second and third week of May, the MJO signal weakened and remained relatively stationary over the Western Hemisphere (Phase 1), with also the influence from other tropical waves. This signal then strengthened again and propagated rapidly eastwards over the Indian Ocean (Phase 2 and 3) in the last week of June. Typically, Phases 1 and 2 bring drier conditions in northern Southeast Asia while Phases 2 and 3 tend to bring wetter conditions to the western Maritime Continent in June. Therefore, the MJO may have contributed to the drier conditions over southern Mainland Southeast Asia and wetter conditions over the western Maritime Continent in June.

Figure 3: The MJO phase diagram. The diagram illustrates the movement of the MJO through different phases, which correspond to different locations along the equator (denoted in the text with the first day of the month in blue and the last day of the month in red). The distance of the index from the centre of the diagram is related to the strength of the MJO. Values within the grey circle are considered weak or indiscernible (data from the Bureau of Meteorology, Australia).

2.2 Over the tropical Pacific Ocean, La Niña conditions were present but show signs of weakening. Sea surface temperatures in the Nino3.4 region (used to monitor ENSO) and the atmospheric indicators over the tropical Pacific Ocean were weakening, indicating weak La Niña conditions in June. La Niña events tend to bring wetter-than-average conditions to much of the Maritime Continent during the June to August period. Over the Indian Ocean, there were signs of negative Indian Ocean Dipole development as the Dipole Mode Index (DMI), which is used to measure the Indian Ocean Dipole (IOD) signal, became increasingly negative and had transited into the negative phase in June. Negative IOD tends to bring wetter-than-average conditions for much of Southeast Asia.

July 8, 2022

Subseasonal Weather Outlook (11 – 24 July 2022)

Issued: 8 July 2022
First forecast week: 11 July – 17 July
Second forecast week: 18 July – 24 July

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

Wetter conditions are expected over much of the southern and eastern Maritime Continent in the next fortnight (11 – 24 July). Wetter conditions are also expected over much of the central and eastern Mainland Southeast Asia in Week 1 (11 – 17 July) and predicted to ease over southern parts of Mainland Southeast Asia in Week 2 (18 – 24 July).

Warmer than usual temperatures are expected over most of Myanmar in the next fortnight (11 – 24 July).

Since early July, a moderate Madden-Julian Oscillation (MJO) was present over the western Maritime Continent (Phase 4). While some models predict this signal to continue propagating through the eastern Maritime Continent (Phase 5) and Western Pacific (Phase 6) by Week 2, others predict the MJO signal to decay.

Review of Regional Haze Situation for June 2022

1.1 Southwest Monsoon conditions persisted over the ASEAN region in June 2022. Over the Philippines and much of the southern ASEAN region, the prevailing winds blew mainly from the southeast. Regions close to the Equator experienced winds that were light and variable in direction. Over the Mekong sub-region, the prevailing winds were mostly southwesterly (Figure 1).

1.2 During the review period, rainy weather prevailed over most parts of the ASEAN region. In particular, moderate to heavy showers fell on several days over western Borneo, as well as central and northern Sumatra, southern Sulawesi, northern Viet Nam, and northern Philippines. Drier conditions were observed over the Lesser Sunda Islands, coastal Viet Nam, central Myanmar, as well as northern parts of Thailand and Lao PDR (Figure 1).

Figure 1: Average Daily Rainfall and Mean Winds for June 2022. (Source: JAXA GsMaP and GFS, respectively)

1.3 Hotspot activity in the ASEAN region was mostly subdued in June 2022 due to the prevailing wet weather conditions. The total number of hotspots was lower or comparable to previous years for the same period (Figure 2 and 3), except in Lao PDR where a slightly higher number of hotspots was detected.

Figure 2: Hotspot counts for the southern ASEAN region for the month of June (2018 – 2022). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2018 are based on the Suomi-NPP satellite.]

Figure 3: Hotspot counts for the northern ASEAN region for the month of June (2018 – 2022). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2018 are based on the Suomi-NPP satellite.]

1.4 In June 2022, isolated to scattered hotspots were detected in parts of Viet Nam and Cambodia while few to isolated hotspots were detected in most parts of the southern ASEAN region on some days. However, these hotspots were short-lived and did not contribute to any significant smoke haze. During a brief period of drier weather toward the end of the review period, a slight increase in hotspots was detected in Sumatra and Borneo (Figure 4).

Figure 4: Distribution of hotspots detected in June 2022 based on NOAA-20 satellite surveillance.

1.5 The overall fire intensity of hotspots detected over the ASEAN region was low during the review period of June 2022. There was no significant smoke haze observed via satellite imagery and ground reports (Figure 5).

Figure 5: Maximum fire intensity in June 2022 based on NOAA-20 satellite surveillance.

July 1, 2022

Alert20220701 – Start of Dry Season for the Southern ASEAN Region

Start of Dry Season for the Southern ASEAN Region

Over the past week, there have been periods of dry weather observed over many parts of southern ASEAN region. Based on surveillance by the NOAA-20 satellite, a total of 5 and 3 hotspots were detected in Sumatra, and 2 and 0 hotspots were detected in Peninsular Malaysia on 29 and 30 June 2022, respectively.

With drier conditions expected to persist over much of the southern ASEAN region in the coming weeks, there remains a risk of increased hotspot activity and smoke haze development. The traditional dry season is expected to persist until October 2022.

ASMC Media Release – Start of southern ASEAN dry season

Events – start of dry season in the southern ASEAN region – 2022

MEDIA RELEASE

START OF DRY SEASON IN THE SOUTHERN ASEAN REGION

Singapore, 1 July 2022 – The ASEAN Specialised Meteorological Centre (ASMC) has declared the start of the traditional dry season for the southern ASEAN region¹. The dry season for the region is associated with the onset of the Southwest Monsoon and is likely to stretch into October 2022.

1 The prevailing La Niña conditions in the equatorial Pacific Ocean are forecast to continue weakening, with either La Niña or neutral conditions expected for the rest of the year. In addition, a negative Indian Ocean Dipole (IOD) is developing in the equatorial Indian Ocean and is expected to become established by August 2022. These two climate phenomena – La Niña and negative IOD, are expected to bring above-normal rainfall to most parts of the southern ASEAN region between July and October 2022.

2 Wet weather conditions in many parts of the southern ASEAN region during the first half of this year have helped to keep the fire hotspot and smoke haze situation generally subdued. In the coming months, although above-normal rainfall is forecast, there is still a risk of increased fire hotspot activity and smoke haze development during occasional periods of extended dry and warm weather.

3 Based on ASMC’s regional weather outlook, the overall smoke haze situation in the southern ASEAN region this year is not likely to be severe like that in 2015 and 2019, when there was prolonged drier-than-normal weather caused by a strong El Niño and a strong positive IOD respectively. Nonetheless, some transboundary haze may occur if the prevailing southeasterly to westerly winds blow smoke haze from persistent fires to neighbouring countries. Early preventive measures and vigilance are advised to mitigate land and forest fires during the dry season.

4 For regular and ad-hoc updates of the regional weather and smoke haze situation and early warnings, please visit the ASMC website at https://asmc.asean.org.

[1] The southern ASEAN region comprises of Brunei Darussalam, Indonesia, Malaysia, Singapore and southern Thailand.