TEMPO.CO, Jakarta - The Meteorology, Climatology, and Geophysics Agency (BMKG) predicts that the onset of the 2026–2027 rainy season will be delayed from its usual cycle due to intense El Nino activity. This climate event, occurring alongside a positive Indian Ocean Dipole (IOD), is disrupting wet season patterns across several Indonesian regions.
The agency's head Teuku Faisal Fathani stated that the combined influence of El Nino and positive IOD has prolonged dry conditions, which could worsen in certain areas. "Rain is coming late and occurring for a shorter period," Faisal said during a virtual press conference on Tuesday, September 22, 2026.
During the briefing, Faisal presented sea surface temperature anomaly monitoring data from the Pacific Ocean's Niño 3.4 region as of late August 2026. The temperature anomaly reached +2.83, while the ENSO index for the July-August-September (JAS) period stood at +2.63, indicating a strong El Nino. Meanwhile, the IOD index recorded +0.376 in August and is projected to remain in a positive phase through the end of the year.
BMKG Deputy for Climatology Ardhasena Sopaheluwakan noted that the arrival of the rainy season will vary across the archipelago. A total of 185 season zones (ZOM), representing 24.66 percent of Indonesian territory, will enter the rainy season in November 2026, while 266 zones (17.31 percent) will follow in December.
Regions expecting rains to start in November include parts of Sumatra, Java, Kalimantan, Bali, West Nusa Tenggara (NTB), and isolated areas in East Nusa Tenggara (NTT) and Sulawesi. This outlook also covers portions of North Maluku, Maluku, northern West Papua, and southern South Papua.
The rainy season is expected to begin in December across parts of Lampung, most of Java, parts of South Kalimantan, and the majority of Bali, NTB, NTT, and Sulawesi, as well as sections of North Maluku, Maluku, and southern South Papua.
Regions forecast to hit peak rainfall in December 2026 include most of Sumatra and Kalimantan, parts of North Sulawesi, southern coastal Gorontalo, isolated areas in Central Sulawesi, most of West Sulawesi, and parts of North Maluku. Similar conditions are expected in western Southwest Papua, parts of West Papua, northern Papua, eastern Central Papua, and western South Papua.
Several areas are projected to reach their peak rainy period in January 2027, including southern Riau, the central Riau Islands, parts of Jambi, northern Bengkulu, the Bangka Belitung Islands, western South Sumatra, northern Lampung, parts of Java, and central Bali. BMKG anticipates matching conditions in western NTB, parts of NTT and West Kalimantan, most of Central Kalimantan, sections of East and South Kalimantan, portions of Sulawesi, parts of North Maluku, western Maluku, and areas across Papua.
The agency highlighted that another set of regions will reach peak wet weather in February 2027, including central Lampung, most of Java, and most of Bali. Other areas expected to follow this timeline include parts of NTB, most of NTT, southern West Sulawesi, parts of South Sulawesi, southern Southeast Sulawesi, sections of Maluku, and most of Papua.
According to Ardhasena, the total duration of the 2026–2027 rainy season will be shorter than average across 482 season zones, covering 51.90 percent of Indonesia's landmass. Conversely, 60 season zones (8.58 percent) are expected to experience a longer rainy season. "Meanwhile, conditions matching normal historical baselines will occur in 40 season zones, or 5.06 percent of Indonesia's land area," he said.
Read: BMKG Warns of Year-End Disasters as Rainy Season Approaches
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