December 11, 2025 | 02:16 pm
TEMPO.CO, Jakarta - The Meteorology, Climatology, and Geophysics Agency (BMKG) continues its intensive 24-hour monitoring of the development of tropical cyclone seed 91S forming in the Indian Ocean west of Lampung Province. According to BMKG's analysis, 91S could have indirect impact on the amount of rainfall in certain parts of Sumatra.
BMKG head Teuku Faisal Fathani urges residents to remain calm but vigilant. The current active atmospheric dynamics are affecting the rainfall intensity in the Sumatra region, and cyclone seed 91S could trigger an increase in moderate to heavy rainfall in parts of Aceh, North Sumatra, West Sumatra, Bengkulu, and Lampung.
"The public must also be aware of the potential for high waves in the Indian Ocean west of Nias to the south of Banten, as well as in the southern part of the Sunda Strait," Faisal said in a written statement on Thursday, December 11, 2025.
Previously, BMKG detected tropical cyclone 91S on December 7, 2025, at 07:00 a.m. local time through monitoring by the Tropical Cyclone Warning Centre (TCWC) in Jakarta. Since its formation, BMKG has been conducting intensive 24-hour monitoring to observe its movement, intensity, and potential impacts.
BMKG emphasizes there is little potential for 91S to develop into a tropical cyclone and make landfall. Therefore, BMKG advises the affected regions to remain calm and frequently update weather information from BMKG.
Meanwhile, Deputy of Meteorology at BMKG, Guswanto, said that the latest analysis revealed that 91S is moving south to southwest from the afternoon and evening of December 11. The system is expected to continue moving southwest, away from Indonesia, on December 12, 2025.
He ensured that his agency has coordinated with the National Disaster Management Agency (BNPB) and several Regional Disaster Management Agencies (BPBD). "To ensure that mitigation runs optimally according to the potential weather conditions influenced by the presence of 91S," said Guswanto.
Director of Public Meteorology at BMKG Andri Ramdhani urges the public, especially in the west-south coast of Sumatra to the Banten region, to be cautious of the potential for heavy rain, strong winds, and high waves.
He mentioned that the shipping, fishing, and maritime transportation sectors are advised to adjust their operational activities based on the applicable high wave warnings. He stated that local governments through BPBD are required to ensure preparedness to face potential floods and other weather disturbances. Solid cross-sectoral collaboration is the key to creating harmony between early warning systems and early action.
BMKG, he said, is committed to update official information regularly on the development of cyclone seed 91S, including high waves, daily weather information, and weekly weather outlook through all BMKG's official channels.
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