Fourteenth Session of the ASEAN Climate Outlook Forum (ASEANCOF-14)
21st May 2020, Online Correspondence
Consensus Bulletin for June-July-August (JJA) 2020 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 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 ASEAN region through pooling the expertise of ASEAN National Meteorological Services.
The fourteenth ASEANCOF (ASEANCOF-14) was organised by Meteorological Service Singapore as host of the ASEAN Specialised Meteorological Centre. Representatives from National Meteorological and Hydrological Services (NMHSs) of ASEAN Member States created a consensus forecast for the summer monsoon 2020 in the ASEAN region. The consensus for June-July-August (JJA) 2020 outlooks was achieved through online correspondence, including questionnaires and online discussions regarding the current conditions and predictions for the Southeast Asia region. In particular, the forum considered the possible influence of the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on the climate system over Southeast Asia.
Conditions and Outlook
Recent analysis of sea surface temperature (SST) anomalies over the equatorial Pacific indicate near average SSTs and ENSO neutral conditions are present. The international climate outlooks predict ENSO neutral conditions are likely to continue during JJA 2020, although there is potential that La Niña conditions may begin to develop towards the end of the period or later in the year. The previous positive Indian Ocean Dipole (IOD) weakened in January 2020 and the current IOD state is neutral. Some models predict a negative IOD event to develop during JJA, but with relatively high uncertainty at this time of year.
The consensus from ASEANCOF is an increased chance of a negative IOD event to develop during JJA while ENSO conditions are most likely to remain neutral during JJA. The Southwest (SW) Monsoon is expected to be weaker than normal, based on model predictions. However, local rainfall for some regions will depend on tropical cyclone activity, which is uncertain. For most countries, the onset of the SW monsoon is expected to be near-normal. However, the SW monsoon related rainfall may arrive later than normal for a few countries (Thailand and Viet Nam). Overall, the tropical cyclone frequency is expected to be near normal for JJA 2020.
Taking into consideration the national level forecasts, the present state of the climate, and the forecasts available from GPCs and other global centres, the forum agreed on the following consensus-based outlook for JJA 2020 for the Southeast Asia region:
For the upcoming Northern Hemisphere summer season (June-July-August), normal- to above-normal rainfall is expected over much of the equatorial region (Brunei, Malaysia, Singapore, and northern parts of Indonesia) as well as northern Viet Nam and coastal central Viet Nam. Normal- to below-normal rainfall is expected over southern Myanmar, southern and northeastern Thailand, northern Philippines, parts of Lao PDR, and southeastern Indonesia. Elsewhere, normal or climatological probabilities are forecasted.
Above-normal temperature is expected over most of Southeast Asia, although the probability of above-normal temperature is lower over Viet Nam and parts of Indonesia, and northern Philippines.
Refer to Annex A for reference on what is meant by “above, near, or below normal” in the outlook. For more information on the 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 2020
The following maps provide the probabilistic outlooks for JJA 2020 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
The Forum would like to convey its appreciation to the National Meteorological Services of the ASEAN Member States for sharing their national-level forecasts, the Global Producing Centres and other participating international climate modelling centres for their products and expertise made available for this Climate Outlook Forum.