BMKG: Aceh on Alert for Heavy Rain on 18 October 2026

Indonesia's Meteorology, Climatology and Geophysics Agency (BMKG) warned of potential extreme weather in several parts of Indonesia on Sunday, 18 October 2026. According to the forecast issued on Saturday (17/10/2026), Aceh province is on alert status for heavy to very heavy rain.

Nine other provinces are also on alert for moderate to heavy rain: West Kalimantan, Central Kalimantan, Papua, West Papua, Southwest Papua, Highland Papua, Riau, West Sumatra and North Sumatra.

Today's warning follows BMKG's forecast for Saturday, 17 October 2026, which also listed moderate to heavy rain in 12 regions, including Aceh, North Sumatra, Riau, Riau Islands, Kalimantan and Papua. BMKG data show heavy to extreme rain already hit several areas on 13–15 October 2026, with daily rainfall reaching 187 millimetres in Aceh, 95 mm in North Sumatra, 69 mm in West Sumatra and 63 mm in Southwest Papua.

9 Provinces on Alert, 4-Metre Waves Threaten the Seas

BMKG also warned of sea waves of 2.5 to 4 metres in the western Indian Ocean, from the Mentawai Islands to Lampung. Coastal flooding or tidal floods are a concern along the coasts of Riau Islands, Jakarta, West Java, Bali, West Nusa Tenggara, South Kalimantan, Central Kalimantan and Maluku.

A cyclonic circulation is being monitored in the Indian Ocean west of Aceh and the South China Sea south of Vietnam, triggering convergence zones and wind deceleration. BMKG also warned of possible lightning in Tanjung Pinang and the growth of cumulonimbus clouds that could endanger flights along several routes, including the Malacca Strait, the Indian Ocean west of Aceh, the North Natuna Sea, and the waters of Sumatra, Kalimantan, Sulawesi and Papua.

Residents are advised to adjust their activities and travel to the weather conditions and to follow the latest information through BMKG's official channels. Although 76 percent of Seasonal Zones are still in the dry season, atmospheric dynamics can still produce locally heavy rain.

Strong El Nino and a Delayed Rainy Season

BMKG explained that a very strong El Nino and a positive phase of the Indian Ocean Dipole (IOD) are still influencing Indonesia's atmospheric conditions. In early October 2026, the sea surface temperature anomaly in the Nino3.4 region reached +3.33 degrees Celsius, while the three-monthly ENSO index for August–September–October stood at +3.08 and the IOD index at +0.703.

"The combination of El Nino and IOD occurring simultaneously is worsening and prolonging the drought period across much of Indonesia, so the rainy season arrives late and lasts shorter," said BMKG chief Teuku Faisal Fathani at a press conference on 22 September 2026.

BMKG predicts the onset of the 2026/2027 rainy season will lag behind climatological averages across 529 Seasonal Zones, equivalent to 61.08 percent of Indonesia. BMKG climatology deputy Ardhasena Sopaheluwakan said 185 zones (24.66 percent of the country) are expected to enter the rainy season in November 2026 — covering parts of Sumatra, Java, Kalimantan, Bali, NTB, NTT, Sulawesi, North Maluku, Maluku, northern West Papua and South Papua. Meanwhile 266 zones (17.31 percent) will only enter the rainy season in December 2026.