Twentieth Session of the ASEAN Climate Outlook Forum (ASEANCOF-20)
25, 26, 30 May 2023, ASMC
Consensus Bulletin for June-July-August (JJA) 2023 Season
The ASEAN Climate Outlook Forum (ASEANCOF) is an avenue to collaboratively develop consensus-based seasonal climate outlooks and related information on a regional scale. The forum’s outlook and its activities contribute significantly to one of the key roles of the ASEAN Specialised Meteorological Centre (ASMC), which is to conduct climate and seasonal prediction for the Association of Southeast Asian Nations (ASEAN) region through pooling the expertise of ASEAN National Meteorological and Hydrological Services (NMHSs). In 2021, the ASEANCOF Working Group was established with the goal to guide and support the long-term development of ASEANCOF, in particular with regard to the implementation of objective outlooks.
The Twentieth session of ASEANCOF (ASEANCOF-20) was organised by ASMC and the ASEANCOF Working Group. Participants from the NMHSs of ASEAN Member States created a consensus forecast for the boreal summer monsoon 2023 in the ASEAN region. The consensus for the June-July-August (JJA) 2023 outlook was achieved through an online session, which included presentations from different NMHSs, questionnaires, and discussions regarding the current climate conditions and predictions for Southeast Asia. In particular, ASEANCOF considered the influence of the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on the climate system over Southeast Asia. The theme of ASEANCOF-20 was ‘Advances in climate services on subseasonal to seasonal timescales’. On the last day of ASEANCOF-20, a sharing session was held on the impact of El Niño on Southeast Asia, involving NMHSs and users of ASEANCOF information.
Conditions and Outlook
Recent analysis of sea surface temperature (SST) anomalies over the equatorial Pacific shows average to slightly above-average SSTs across most of the equatorial Pacific Ocean, and along with atmospheric indicators such as trade wind strength and cloudiness, indicate ENSO-neutral conditions. In the Indian Ocean, the Indian Ocean Dipole (IOD) is also neutral.
An El Niño is highly likely to become established during JJA 2023. After JJA 2023, most global climate models predict the El Niño conditions to continue until the end of the year. The strength of the upcoming El Niño is uncertain, although some models are predicting that it could be moderate to strong.
A positive IOD is predicted to become establish during JJA 2023. Most models predict the IOD to return to neutral before the end of 2023.
The onset of the Southwest monsoon season has been or is expected to be later than average for much of Mainland Southeast Asia, while near average for the rest of the region. Over western parts of the region, the strength of the Southwest monsoon is expected to be stronger than average, with weaker than average or near average strength for the rest of the region, based on model predictions and supported by the predicted El Niño conditions.
During JJA 2023, tropical cyclone frequency is predicted to be below to near average around the South China Sea and the Philippine Sea and near average around the Bay of Bengal.
Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from the GPCs, ASEANCOF-20 agreed on the following consensus-based outlook for JJA 2023 over the ASEAN region:
Over most of the southern ASEAN region, below- to near-normal rainfall is predicted. The exceptions include northeastern Borneo and eastern Maritime Continent where near- to above-normal rainfall is predicted.
Over much of the northern ASEAN region, a mix of near- to above-normal rainfall is predicted. Above-normal rainfall is predicted over parts of southwestern and southeastern Mainland Southeast Asia, while near- to above-normal rainfall is predicted elsewhere over this region. Above-normal rainfall is predicted for much of the western half of the Philippines, with near- to above-normal rainfall elsewhere1.
Near- to above-normal temperature is predicted over Southeast Asia1. Near-normal temperature is predicted over parts of the southern Maritime Continent, including southern Sumatra and Java. Near- to above-normal temperature is predicted over the southwestern and southeastern parts of Mainland Southeast Asia, Malaysia, and the Philippines. Elsewhere in Southeast Asia, above-normal temperature is predicted.
1This is based on the climatology period 1991-2020. However, at the national level, Myanmar is using the 1981-2010 climatology as their base period.
Refer to Annex A for reference on what is meant by “above, near, or below normal” in the outlook. For more information on the boreal (Northern Hemisphere) summer monsoon outlook and further updates on the national scale, the relevant NMHSs should be consulted (see Annex B).
Consensus Maps for JJA 2023 Season
The following maps provide the probabilistic outlooks for JJA 2023 season in terms of tercile categories of “Above Normal” (AN: upper tercile), “Near Normal (NN: middle tercile) and “Below Normal” (BN: lower tercile).
PROBABILISTIC RAINFALL OUTLOOK
PROBABILISTIC TEMPERATURE OUTLOOK
ASEANCOF would like to convey its appreciation to the NMHSs of the ASEAN Member States for sharing their national level forecasts, the GPCs, the Southeast Asia Regional Climate Centre – Network, RIMES, UN ESCAP, and other partners of ASEANCOF for sharing their products and expertise, and the World Meteorological Organization Regional Office in Asia and the Southwest Pacific (WMO-RAP) for their continued support of ASEANCOF.