Indonesia’s meteorological agency BMKG has issued a weather advisory for 1 January 2026, warning of thunderstorms, increased winds and high seas that will affect wide areas of the archipelago. Cloudy conditions with light to moderate rain will dominate, while localised storms with lightning are expected in several provinces.
Indonesia weather forecast key warnings
BMKG linked the unsettled conditions to Tropical Cyclone 90S, which was observed in the Indian Ocean south of Lampung. The system is enhancing wind speeds to between 6 and 25 knots in affected waters and contributing to the build-up of rain-bearing clouds.
Authorities report the strongest winds are present over the Indian Ocean, the Java Sea, the Makassar Strait and the Banda Sea. These winds are also elevating wave heights, prompting BMKG to issue maritime cautions for multiple sea lanes around the country.
On land, the agency advised residents in parts of Sumatra, Java, Kalimantan and Sulawesi to remain vigilant for thunderstorms that may bring heavy rainfall, lightning and brief local flooding. Urban areas and transport hubs should be prepared for sudden downpours that can disrupt travel and public services.
City-by-city outlook
BMKG provided targeted forecasts for major urban centres. In Sumatra, Tanjung Pinang is expected to be cloudy while Banda Aceh, Bandar Lampung, Medan, Pangkal Pinang and Padang will see light rain. Palembang faces moderate rain and Bengkulu, Jambi and Pekanbaru are at risk of thunderstorms.
Across Java, light rain is forecast for Jakarta, Semarang and Surabaya, with Bandung and Serang expecting moderate rain. Yogyakarta faces thunderstorm conditions.
Bali and Nusa Tenggara will be generally fairer, with Denpasar partly cloudy, Mataram cloudy and Kupang seeing light rain. In Kalimantan, light rain is likely in Samarinda, Tanjung Selor, Pontianak and Palangkaraya, while Banjarbaru may experience thunderstorms.
Sulawesi will see varied conditions: Manado and Gorontalo are expected to be cloudy, Kendari, Mamuju and Palu should receive light rain, and Makassar is forecast to have thunderstorms. Maluku and Papua will mainly see cloudy skies with light rain in several locations including Jayapura, Ambon and Sorong.
Marine warnings and safety advice
BMKG listed numerous sea areas with forecast wave heights of 1.25 to 2.5 metres. These include the northern Malacca Strait, stretches of the Indian Ocean off Aceh and Java, parts of the Karimata Strait, the northern Pacific waters near Maluku and Papua, and multiple seas around Bali, Nusa Tenggara and Maluku.
Higher seas between 2.5 and 4 metres have been forecast for the North Natuna Sea and certain sectors of the Indian Ocean. BMKG urged fishermen, ship operators and coastal communities to monitor updates and take precautionary measures. Small craft should avoid affected waters and larger vessels should take caution when routing through those sea lanes.
BMKG maintains regular bulletins and recommends checking the agency’s website and official social channels for real-time updates. Local disaster management offices and maritime authorities have been asked to coordinate closely to reduce the risk to life and property during the unsettled weather period.
Residents are advised to secure loose outdoor items, avoid low-lying riverside areas during heavy rain and follow instructions from local authorities should evacuation or other emergency measures be necessary.
Key Takeaways:
- BMKG warns of thunderstorms across Sumatra, Java, Kalimantan and Sulawesi in the Indonesia weather forecast.
- Tropical Cyclone 90S in the Indian Ocean is increasing wind speeds and driving cloud formation.
- High waves of 1.25–2.5m expected in several seas; 2.5–4m seas near Natuna and parts of the Indian Ocean.
- Fishermen, mariners and coastal communities are urged to follow updates from BMKG.
