December 1, 2025 | 06:26 pm
TEMPO.CO, Jakarta - Indonesia’s Meteorology, Climatology, and Geophysics Agency (BMKG) said it had warned local governments well in advance about the formation of Tropical Cyclone Senyar, which triggered catastrophic flooding across Sumatra last week.
According to BMKG Head Teuku Faisal Fathani, the cyclone brought intense, prolonged rainfall across the island and could be detected up to eight days before it fully developed.
“At our regional offices in Aceh, North Sumatra, and West Sumatra, BMKG issued warnings eight days before the cyclone formed. These alerts were repeated four days prior, and again two days before impact,” Teuku said during a coordination meeting on Christmas and New Year preparedness at the Ministry of Home Affairs in Jakarta on December 1, 2025.
He said that while some regional leaders acted quickly and passed the warnings to their teams on the ground, all local governments need to treat early cyclone alerts with urgency. He warned that tropical cyclones can bring extremely heavy rainfall and trigger serious floods and landslides.
BMKG operates five major regional monitoring centers, each authorized to issue direct warnings to provincial governments.
“They can be invited for consultations to help prepare for future threats,” Teuku said.
A Rare Cyclone Driven by Atmospheric Anomalies
Teuku explained that Tropical Cyclone Senyar formed due to unusual atmospheric conditions. Indonesia is generally not located in the world’s cyclone-prone corridors.
Most cyclones form in the western Pacific, north of Papua, before sweeping across the Philippines and moving toward the South China Sea. The Philippines, for instance, can experience more than ten cyclones a year.
Cyclones rarely approach the equator because the Coriolis effect, the force generated by Earth’s rotation, is too weak. As a result, cyclones typically form only at latitudes above five degrees north or south.
“But this time, atmospheric anomalies, cold surges, and other weather disturbances created conditions for Cyclone Senyar to form in the Malacca Strait,” he said.
Warm sea temperatures in the strait also intensified cloud formation, amplifying rainfall and disaster risk, even though Senyar was classified as a lower-level cyclone.
Why the Flooding Turned Catastrophic
Teuku explained that Senyar became trapped between Sumatra and Peninsular Malaysia, rotating in place and producing torrential rain for more than two or three consecutive days.
“At our Langsa monitoring post alone, rainfall reached 380 millimeters, which is equivalent to a month’s worth of rain falling in a single day,” he said. “This shows how powerful the impact of Cyclone Senyar was.”
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