seasonal forecast for September, October, November

Updated 19 September 2017

The prevailing Southwest Monsoon conditions are expected to extend into mid-October 2017. During this season, prevailing winds are forecast to blow from the southeast or southwest. The development of tropical cyclones in the Western Pacific Ocean and/or the South China could bring heavy rainfall to parts of the ASEAN region, particularly over the Philippines and Vietnam.

For the southern ASEAN region, occasional periods of dry weather conditions may prevail, and could lead to an escalation in hotspot activities in the fire-prone provinces of Sumatra and Kalimantan. Hence vigilance should be stepped up for any escalation of fire activities during periods of drier weather

Towards the end of September 2017, the monsoon rain band is forecast to lie between latitudes 5oN and 20oN, and this could bring above-normal rainfall to parts of the northern ASEAN region and drier than usual conditions over the southern ASEAN region

For the September-October-November season, near-normal rainfall is forecast for most parts of the northern ASEAN region. In the southern ASEAN region, near-normal rainfall is forecast for most parts of the region, except for South Sumatra where slightly below-normal rainfall is expected.

In the second half of October 2017, the Southwest Monsoon season is expected to transit into the inter-monsoon season. During this period, the prevailing winds in the region are forecast to become light and variable in direction, and an increase in shower activities is expected. Hotspot activities in the southern ASEAN region are likely to be subdued with the expected occurrence of more shower activities in the region during the Southwest Monsoon season.



  • 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)