Jakarta. The Meteorology, Climatology and Geophysics Agency (BMKG) warns of unusually heavy rainfall during what is typically the dry season, with weather anomalies expected to bring extreme rain across parts of the country from July to September.

The unseasonal downpours, already hitting parts of Java and Papua, are being driven by a combination of warmer sea surface temperatures, weakening Australian monsoon winds, and active short-scale atmospheric waves, according to Indra Gustari, Head of Climate Index Prediction at BMKG.

“Rainfall this July, August, and September will be higher than average for the dry season due to these anomalies,” Indra said during a briefing in Jakarta on Wednesday. While rainfall volumes will still be lower than during the wet season, they are significantly above normal dry-season levels, he added.

Rainfall recorded on July 5-7 exceeded 100 millimeters per day in several areas, meeting BMKG’s criteria for extreme weather, Indra said.

Indonesia’s rainy season is expected to begin in October and last through February.

The anomalies are driven by warmer-than-average sea surface temperatures, which increase evaporation; weaker Australian monsoon winds, which typically reduce rainfall; and active Madden-Julian Oscillation (MJO), Kelvin, and Rossby waves that intensify local precipitation.

Currently, only about 30 percent of Indonesia’s nearly 700 seasonal zones have entered the dry season, leaving many areas still susceptible to heavy rain. The agency highlighted Java, Bali, Nusa Tenggara, Kalimantan, and Papua as regions with continued high rainfall potential.

BMKG has urged local governments and communities, particularly those in flood- and landslide-prone areas, to prepare for potential disasters during this period, including improving drainage systems, keeping waterways clear of waste, and maintaining infrastructure to mitigate the impact of heavy rains.

“Even in this dry season, we need to remain alert for hydrometeorological disasters due to the potential for wet hydrometeorological hazards such as floods and landslides,” Indra said, adding that the risks will persist through the transition to the wet season in late 2025.

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