December 24, 2025 | 01:02 pm
TEMPO.CO, Jakarta - The Meteorology, Climatology, and Geophysics Agency (BMKG) forecasts that most of Indonesia will have 1,500 to 4,000 millimeters of yearly rainfall next year. Ardhasena Sopaheluwakan, the Deputy of Climatology at BMKG, assured that such variations in rainfall are still considered normal in Indonesia.
He explained that areas with a low level of rainfall, around 1,500 mm per year, include Bali, West Nusa Tenggara, East Nusa Tenggara, the east coast of Sumatra, the east coast of Kalimantan, and several other regions. "Regions with significantly high rainfall, 4,000 mm per year or even higher, are the ones that we need to be wary of," Ardhasena said during the 2026 BMKG Climate Outlook on Tuesday, December 23, 2025.
These areas include the central part of Central Java, West Java, most parts of Kalimantan, the central region of Sulawesi, most parts of Papua, and the west coast of Sumatra facing the Indian Ocean. According to Ardhasena, the high rainfall in the west coast of Sumatra is also influenced by the geographical conditions and regional climate. "The climate phenomena are greatly influenced by the sea heat from the Indian Ocean," he explained.
However, BMKG generally considers the nature of rainfall in 2026 to be within the normal category. "Meaning, the conditions we will face in 2026 have frequently occurred in previous years or in the 1991-2020 climatological reference," he added.
Regions with Chance for Very Heavy Monthly Rainfall
Ardhasena also presented the monthly rainfall forecast throughout 2026. For January, the rainfall is predicted to be in the medium to high category, with a very high chance of rainfall in Banten, West Java, Central Java, Bali, East Nusa Tenggara, and South Sulawesi.
In February, the rainfall is generally expected to be in the low to high category, with the potential for substantial rain in Central Java and South Sulawesi. From March to April 2026, high chance of downpour is predicted in Central Java and Central Papua.
Entering May to June, as Indonesia begins to transition to the dry season, the rainfall is forecast to be in the low to medium category. BMKG warns that the potential for very low rainfall may start to occur in West Nusa Tenggara and East Nusa Tenggara.
From July to September 2026, which marks the peak of the dry season, the rainfall is generally in the low to medium category. Regions with potentially very low rainfall include East Java, Bali, West Nusa Tenggara, and East Nusa Tenggara.
Moving on to October 2026, some western regions of Indonesia begin to transition to the rainy season. The rainfall is predicted to be in the low to high category, with a high chance of very heavy rain in Aceh.
As for November to December 2026, BMKG predicts that the rainfall will again be in the medium to high category as the rainy season sets in. The potential for very heavy rain is likely to occur in Aceh, West Sumatra, Bengkulu, Banten, West Java, Central Java, and South Sulawesi.
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