Long-range Forecasting

YEAR

TOPIC

YEAR

TOPIC

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Bulletin

09 JUN 2026

ASEAN Climate Outlook Forum

Twenty Sixth Session of the ASEAN Climate Outlook Forum (ASEANCOF-26)

19– 22 May 2026, Online

Twenty Sixth Session of the ASEAN Climate Outlook Forum (ASEANCOF-26)

The twenty-sixth session of ASEANCOF (ASEANCOF-26) was organized by the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA), Regional Multi-Hazard Early Warning System for Africa and Asia (RIMES), ASMC, the ASEANCOF Working Group, and WMO. This included two prior training sessions: firstly, an introduction to the Seasonal Fundamentals eLearning (pilot version for ASEANCOF) by the UK Met Office; secondly, training and discussion on the Relative Oceanic Niño Index (RONI), by NOAA, Bureau of Meteorology (BoM) Australia, ASMC, and the Meteorological Service Singapore (MSS). During the second training session, participants agreed to adopt RONI alongside other Niño indices for monitoring ENSO in the region.

CONDITIONS AND OUTLOOK

Recent sea surface temperature anomalies over the equatorial Pacific Ocean during April-May 2026 overall indicated El Niño–Southern Oscillation (ENSO) neutral conditions were present. However, persistent warming over most of the Niño regions, together with atmospheric indicators such as decreased cloudiness over most parts of Southeast Asia and anomalous low-level westerlies east of the Philippines, supports the development of El Niño-like conditions. Meanwhile, the Indian Ocean remains in a neutral Indian Ocean Dipole (IOD) phase.
International climate outlooks predict a moderate El Niño is likely to develop during June to August (JJA) 2026. After JJA, most models predict continued strengthening into a strong to very strong El Niño, while the rest predict only moderate El Niño conditions to persist through the remainder of the year. If a very strong El Niño occurs, this does not necessarily indicate bigger impacts on Southeast Asia’s climate but rather that typical impacts from El Niño events are more likely to occur. The IOD is also predicted to transition to positive IOD conditions through the latter part of 2026, although with less confidence than the predicted El Niño.
The onset of the 2026 Southwest Monsoon season has been or is expected to be near-average across much of the ASEAN region, except over Viet Nam and the Lao People’s Democratic Republic (PDR), where a later-than-average onset occurred. Overall, the strength of the Southwest Monsoon is predicted to be near or stronger than average over most parts of Southeast Asia.

For JJA 2026, tropical cyclone frequency is predicted to be below- to near-average across the region.

RAINFALL

For the upcoming boreal (Northern Hemisphere) summer season (JJA 2026): 

Below-normal rainfall conditions are likely over much of the Maritime Continent, including the southern Philippines, Brunei Darussalam, and Singapore. The exception is over Malaysia, where below- to near-normal or near-normal rainfall is predicted for much of the country, and the central and northern Philippines, where a mix of near- to above-normal rainfall is predicted.

A mix of below- to above-normal rainfall is predicted over mainland Southeast Asia. Below- to near-normal rainfall is predicted over central Thailand, parts of southern Thailand, central Cambodia, and southern Viet Nam. Near-normal rainfall is predicted over the northern half of Myanmar, southern Lao PDR, and mountainous regions of northern Viet Nam and southern Viet Nam. Above-normal rainfall is predicted over coastal and southern Myanmar and parts of northern Lao PDR, with near- to above-normal rainfall over parts of northern Thailand, Cambodia, and Viet Nam.

TEMPERATURE

For the upcoming boreal (Northern Hemisphere) summer season (JJA 2026):
Above-normal temperatures are expected across most parts of Southeast Asia. The exception is over the southern Maritime Continent and parts of northern Viet Nam and northern, southern, and coastal Myanmar, where near- to above-normal temperatures are predicted.

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 D).

CONSENSUS MAPS FOR JJA 2026

The following maps provide the probabilistic outlooks for JJA 2026 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


[1]   For this outlook, near-to above-normal temperature corresponds to 50% probability of above-normal temperature, 40% near-normal, and 10% below-normal.  Further information is in the consensus maps. 

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