Southeast Asia: Annual northeast monsoon season regionwide through at least early April

There is an increased likelihood of flooding, landslides, mudflows, and related disruptions across portions of Southeast Asia, including Brunei, Indonesia, Malaysia, Singapore, and Timor-Leste, during the northeast monsoon period through at least early April. Heavy downpours, flooding, and landslides could affect business, transport, and utility services in many areas of the affected countries throughout the monsoon season. Localized disruptions could persist well after hazardous events have concluded - it could take days or weeks for floodwaters to subside and for authorities to clear landslide debris. Rural communities and informal settlements often suffer the greatest damage and casualties during such events due to their poor infrastructure.

The potential for flooding is highest in low-lying communities near watercourses in recognized floodplains. Rivers such as the Singapore and Kallang in Singapore, the Citarum, Kapuas, and Mahakam in Indonesia, Lois in Timor-Leste, and Pahang and Rajang in Malaysia, as well as their tributaries, regularly overflow their banks during periods of intense rainfall. Flash floods, which often occur with little-to-no warning, can pose a threat to communities downstream of major rivers or dams in the event of infrastructural failure. Urban flooding is possible in areas with poorly maintained, inadequate, or non-existent drainage systems. Storm surges may trigger flooding in coastal areas. Landslides and mudslides are possible in hilly and mountainous areas, including the Maoke Mountains in Indonesia.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters.

Severe weather could also trigger flight delays and cancellations at domestic and international airports across the affected area over the coming months. Authorities may temporarily suspend port operations or close beach fronts if strong winds trigger hazardous sea conditions. Flooding could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation.

Localized business disruptions may occur in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

Health
The threat of disease outbreaks is elevated during the monsoon season. Backflow from drains that has mixed with floodwaters can become trapped in open areas when inundations recede. These stagnant pools often become a breeding ground for mosquitoes and bacteria, increasing the incidence of insect- and waterborne diseases. Exposure to contaminated water from inundated industrial sites, sewer systems, and septic tanks also poses a significant health threat.