Sea temperature in Indonesia

The sea in Indonesia peaks in January, when the water averages around 29°C.

The main swimming season runs from January – December, when surface temperatures stay comfortable for extended sessions.

On average, 12 months a year sit above 20°C — the threshold most swimmers describe as pleasant without a wetsuit.

The coldest month is typically August at around 27°C, when cold-water swimmers dominate the coast.

Indonesia sits in the Southern Hemisphere, so the warmest sea coincides with the December–February summer and the coolest with July–August.

Long-term climatology for Indonesia shows an annual mean sea temperature of 29°C, ranging from 27°C in winter to 29°C at the summer peak.

The seasonal swing is roughly 2°C between the coldest and warmest month — a useful yardstick when comparing years or checking whether the current sea is running above or below average.

Recent decades have trended slightly warmer at Indonesia, in line with regional sea-surface temperature records for the wider basin.

Monthly averages below are drawn from multi-decadal climatology and are updated as new observations arrive.