BMKG Forecasts Delayed Start to Rainy Season Across Sumatra, Java, and Papua
The Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG) forecasts a delay in the start of the 2026-2027 rainy season across 529 Seasonal Zones (ZOM), covering 61.08% of Indonesia. Parts of the archipelago are expected to experience the onset of the rainy season starting in November 2026.
BMKG Deputy for Climatology, Ardhasena Sopaheluwakan, explained that the start of the rainy season in Indonesia will not occur simultaneously. The majority of the region will only begin its rainy season in November 2026 (185 ZOM/24.66% of the area) and December 2026 (266 ZOM/17.31% of the area).
Regions experiencing the rainy season starting in November include parts of Sumatra, Java, Kalimantan, Bali, NTB, a small part of NTT, Sulawesi, North Maluku, Maluku, northern West Papua, and southern West Papua. Meanwhile, the December rainy season will affect parts of Lampung, most of Java, South Kalimantan, most of Bali, most of NTB, most of NTT, most of Sulawesi, most of North Maluku, most of Maluku, and southern South Papua.
Compared to climatological averages, 529 ZOM (61.08% of Indonesia’s landmass) will experience a delayed rainy season. Only 11 ZOM (1.12% of land area) will experience an earlier start, while 26 ZOM (2.15% of land area) will enter the rainy season as normal.
“Although predicted to be shorter, the 2026/2027 rainy season is generally normal across 510 ZOM (69.76% of Indonesia’s landmass). Attention is required for 147 ZOM (18.55% of land area) due to wetter-than-normal rainfall, while only 42 ZOM (11.69%) are predicted to be below normal or drier,” said Ardhasena during a press conference on Tuesday (22/9/2026).
Ardhasena predicts that most of Indonesia will experience the peak of the 2026/2027 rainy season in December 2026 (155 ZOM/36.94% of land area), January 2027 (162 ZOM/25.68% of land area), and February 2027 (190 ZOM/16.79% of land area).
Regions predicted to reach the peak of the rainy season in December 2026 include most of Sumatra, most of Kalimantan, North Sulawesi, the southern coast of Gorontalo, small parts of Central Sulawesi, most of West Sulawesi, small parts of Maluku, western Southwest Papua, small parts of West Papua, northern Papua, eastern Central Papua, and western South Papua.
Areas predicted to peak in January 2027 include southern Riau, central Riau Islands, small parts of Jambi, northern Bengkulu, Bangka Belitung Islands, western South Sumatra, northern Lampung, parts of Java, central Bali, western NTB, parts of NTT, West Kalimantan, most of Central Kalimantan, small parts of East Kalimantan, parts of South Kalimantan, Sulawesi, small parts of North Maluku, western Maluku, and parts of Papua.
Regions predicted to peak in February 2027 include central Lampung, most of Java, most of Bali, most of NTB, most of NTT, southern West Sulawesi, parts of South Sulawesi, southern Southeast Sulawesi, parts of Maluku, and most of Papua.
“Compared to normal, the duration of the 2026/2027 rainy season in Indonesia is predicted to be shorter than normal in 482 ZOM, covering 51.90% of Indonesia’s landmass; longer than normal in 60 ZOM, covering 8.58% of land area; and the same as normal in 40 ZOM, covering 5.06% of land area,” concluded Ardhasena.