seasonal forecast for October, November, December

Updated 12 October 2017

The Southwest Monsoon conditions in the ASEAN region are expected to transition to inter-monsoon conditions in the second half of October 2017 before the onset of the Northeast Monsoon season around late November 2017.

In the northern ASEAN region, the prevailing rainy season is expected to gradually ease in the coming weeks before the onset of the traditional dry season or Northeast Monsoon season later in the year. During the transition period, hotspot activities are expected to remain subdued but a gradual increase in hotspot activities is expected towards the end of the year.

In the coming weeks for the southern ASEAN region, an increase of shower activities are expected, particularly over Java and the eastern parts of Indonesia. However, there could still be brief periods of dry weather conditions which could lead to an escalation in hotspot activities. Vigilance should therefore be maintained for any surge in the hotspot activities during periods of drier weather.

In the third week of October 2017, well above-normal rainfall is expected for Vietnam, Philippines and the surrounding region of Java Sea. However, for parts of Sumatra, Malaysia, Singapore and Brunei, drier than usual conditions can be expected as a tongue of dry air mass from the Indian Ocean is expected to blow over the region. For the last week of October 2017, normal to slightly wetter than usual conditions are forecast for the region.

By late-November and early-December 2017, the strengthening of a high pressure system in north Asia is expected would signal the start of the Northeast Monsoon season. A strengthening of the northeasterly winds can be expected, and the monsoon rain band is forecast to migrate further south. The northern ASEAN region will experience cool and dry weather conditions, while persistent and widespread shower activities are expected to prevail over the southern ASEAN region.

For the upcoming October-November-December season, above-normal rainfall is expected for the Philippines. Near-normal rainfall is forecast for most parts of the Mekong sub-region, except in Thailand where slightly-below normal is expected in October 2017, and slightly above-normal rainfall are expected in the last two months of 2017. In the southern ASEAN region, near-normal to slightly above-normal rainfall are forecast.



  • Legend
  • Above Normal
    (67th to 100th percentile)
  • Slightly Above Normal
    (50th to 83rd percentile)
  • Normal
    (33rd to 67th percentile)
  • Slightly Below Normal
    (17th to 50rd percentile)
  • Below Normal
    (0 to 33rd percentile)