Indonesia weather: Delayed rainy season predicted due to El Niño

The Meteorology, Climatology, and Geophysics Agency (BMKG) reports that the onset of the 2026/2027 rainy season across much of Indonesia is expected to be delayed due to a strong El Niño phenomenon and a positive Indian Ocean Dipole (IOD) trend. Approximately 61 percent of Indonesia's seasonal zones are predicted to experience a later start to the rainy season than normal, with many regions not seeing significant rainfall until November or December 2026.

Regional forecasts show significant variation. In Central Java, the rainy season is expected in November, while areas like Rembang and Pati may see a later onset. In Yogyakarta, the delay is noted as being different from the patterns seen in the last 30 years, with some areas potentially waiting until December. Banten is expected to enter the rainy season in November, with peaks occurring between January and March 2027. In Lampung, the delay is even more pronounced, with some areas not expecting rain until early January 2027.

Despite the delayed season, BMKG has issued warnings for specific areas regarding heavy rain and strong winds for early October 2026, particularly in parts of Sumatra, Java, and Papua. These localized events carry risks of hydrometeorological disasters such as floods and landslides.