Tropical Cyclone 91B Forms Suddenly, Two Regions on Alert for Heavy Rain
Jakarta, CNBC Indonesia — The Meteorology, Climatology and Geophysics Agency (BMKG) is monitoring Tropical Cyclone 91B, which formed at 1am Western Indonesian Time (WIB) on 29 October 2026. The system is within the monitoring area of the Jakarta Tropical Cyclone Warning Centre (TCWC).
BMKG said Tropical Cyclone 91B is currently located in the Andaman Sea, north of Aceh.
“Over the next 24 hours, the system has a MODERATE chance of developing into a tropical cyclone and is forecast to move west-north-west, away from Indonesian territory,” BMKG wrote in a post on its official Instagram account on Thursday, 29 October 2026.
“Although it is moving away, Tropical Cyclone 91B could have indirect impacts until 7am on 30 October 2026,” the agency added.
BMKG said the potential impacts are:
Moderate to heavy rain in Aceh and North Sumatra.
Waves 1.25–2.5 metres high in the northern Malacca Strait.
“Residents in affected areas and users of sea transport are urged to remain alert and continue monitoring official BMKG weather updates,” the agency said.
Warning on the 2026/2027 rainy season
Separately, BMKG forecasts that most parts of Indonesia will begin entering the rainy season in November and December 2026.
According to the agency’s updated 2026/2027 rainy season forecast, released on 2 October 2026, most parts of Indonesia are expected to enter the season in November 2026 (185 seasonal zones, covering 24.66% of Indonesia’s land area) and December 2026 (266 zones, covering 17.31%). The rainy season will begin in northern Sumatra before gradually reaching other parts of the country.
“The start of the rainy season in most parts of Indonesia is forecast to be later than usual (529 zones, covering 61.08% of Indonesia’s land area) or in line with the normal timing (26 zones, covering 2.15%). Most of the country (482 zones, covering 51.90% of its land area) is forecast to experience a 2026/2027 rainy season that is shorter than normal,” BMKG said.
The areas forecast to enter the rainy season in November 2026 include parts of Sumatra, Java, Kalimantan, Bali, West Nusa Tenggara, a small part of East Nusa Tenggara, Sulawesi, North Maluku, Maluku, northern West Papua and South Papua.
BMKG is also monitoring the potential for rain clouds to develop in the short term.
“From 25 October to 2 November 2026, significant rain-cloud development is forecast across much of Sumatra, Java, Kalimantan, North Maluku and parts of Sulawesi,” BMKG head Teuku Faisal Fathani said in a statement on the agency’s official website.
“By contrast, Bali, West Nusa Tenggara and East Nusa Tenggara may continue to experience relatively dry conditions,” he added.