Torrential rains, exceeding 250mm in just two days in Singapore last year, are a common occurrence in Southeast Asia during January due to the monsoon season. The monsoon, derived from the Arabic word for “season,” is a pattern of wind and rainfall that significantly impacts the region.
Understanding the Monsoon
The monsoon is often described similarly to a sea breeze, with wind direction reversing between morning and evening as land and sea temperatures fluctuate. Initially blowing out to sea, the wind shifts inland as the land cools.
Meteorologists define the monsoon by the seasonal movement of the intertropical convergence zone (ITCZ), where northern and southern winds meet. Historically, sailors referred to the ITCZ as the doldrums, an area characterized by calm winds.
Warm, moist air evaporates from tropical oceans and is carried over land by monsoon winds. This air rises, condenses, and forms cumulonimbus storm clouds, resulting in heavy rainfall.
When the ITCZ remains stationary, areas experience a series of intense storms. While vital for agriculture, providing up to 80% of annual rainfall, these storms can also be extremely destructive, sometimes causing widespread flooding.
Europe experiences more evenly distributed rainfall, with dull, wet winters, unlike the dramatic thunderstorms associated with monsoon seasons.
This article was amended on January 3, 2026. An earlier version of the main image caption incorrectly placed Padang in Sri Lanka, rather than Indonesia.
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