Tropical Cyclone Koto is suspected to be the primary cause behind the extreme weather conditions that have battered four regencies in the North Sumatra Province, Indonesia. This raises an important question: What exactly is Cyclone Koto?
According to reports from the National Disaster Management Agency (BNPB), the affected regions include Sibolga, North Tapanuli, Central Tapanuli, and South Tapanuli. The extreme weather, characterized by relentless heavy rainfall for over two days, has tragically triggered widespread floods and devastating landslides across these areas.
The Meteorology, Climatology, and Geophysics Agency (BMKG), through its Tropical Cyclone Warning Center (TCWC) Jakarta, identified two significant weather systems that converged to unleash the extreme weather upon North Sumatra on November 25, 2025. These were Tropical Cyclone KOTO, intensifying in the Sulu Sea, and Cyclone Seed 95B, detected in the Malacca Strait.
BMKG elaborated that Cyclone Seed 95B, situated in the Malacca Strait, played a crucial role by forming extensive convective clouds stretching from Aceh to North Sumatra. This atmospheric condition significantly heightened the potential for torrential rains in the region over recent days, setting the stage for the ensuing disasters.
Concurrently, Tropical Cyclone KOTO, actively developing in the Sulu Sea, induced potent wind shear patterns and drew in a substantial mass of moist air (inflow) towards its center. This interaction dramatically intensified the growth of rain clouds across the western parts of Indonesia, exacerbating the already severe weather conditions.
The combined influence of these two powerful weather systems is deemed responsible for the extreme rainfall. This deluged several areas in North Sumatra, leading to severe flooding, and also triggered dangerous landslides in regions with steep terrain. The relentless downpour caused rivers to overflow their banks and saturated the soil to the point of instability.
In a 24-hour early weather warning, valid from November 25, 2025, at 7:00 PM WIB until November 26, 2025, at 7:00 PM WIB, BMKG projected that Cyclone Seed 95B held the potential to bring moderate to heavy rainfall to Aceh, North Sumatra, West Sumatra, and Riau. Furthermore, strong winds were also anticipated in Aceh and North Sumatra.
Beyond the rainfall and wind, the forecast also warned of hazardous marine conditions. High waves, ranging from 1.25 to 2.5 meters, were predicted for the northern part of the Malacca Strait. Even more critically, waves between 2.5 and 4.0 meters were expected in the central Malacca Strait, the waters east of North Sumatra, and the Indian Ocean stretching from west of Aceh to Nias, posing significant risks to maritime activities.
Tropical Cyclone KOTO’s broader impact was also highlighted, with forecasts indicating moderate to heavy rain in West Kalimantan and the Riau Islands. Additionally, high waves were expected across the Sulawesi Sea, Maluku Sea, Halmahera waters, Southwest Papua to Papua, and the Pacific Ocean north of Maluku–Papua, underscoring the widespread influence of this formidable storm.
What is Tropical Cyclone Koto?
Tropical Cyclone KOTO is classified as a tropical storm that originated from a low-pressure system in the vicinity of the Sulu Sea. According to international meteorological records, as reported by Hypothetical Hurricane, Cyclone KOTO stands out as one of the most potent storms ever to approach Indonesian territory, exhibiting several distinct characteristics:
- It formed from a low-pressure system south of Yap and underwent rapid development as it entered the warm waters around Palau and the Sulu Sea.
- The cyclone experienced rapid intensification, primarily driven by exceptionally high sea surface temperatures in its path.
- At its peak, KOTO achieved wind speeds equivalent to a strong tropical storm, highlighting its significant power.
- Prior to impacting Indonesia, this system had already caused considerable damage in various regions of the Philippines and Malaysia before charting a westward course towards Indonesian waters.
- Interestingly, upon entering the Philippine area of responsibility, the cyclone was temporarily designated as Verbena before being officially named KOTO by the Japan Meteorological Agency (JMA).
This formidable storm’s intensity was notably comparable to that of Typhoon Vamei (2001), with both systems registering approximate wind speeds of 75 miles per hour (mph) upon landfall. KOTO garnered significant international attention not only due to its unusual formation trajectory and rapid intensification but also for the extensive damage it inflicted across multiple Southeast Asian nations.
Summary
Tropical Cyclone Koto is considered the primary cause of extreme weather, including widespread floods and landslides, affecting four regencies in North Sumatra Province. The Meteorology, Climatology, and Geophysics Agency (BMKG) identified two converging systems on November 25, 2025: Tropical Cyclone KOTO in the Sulu Sea and Cyclone Seed 95B in the Malacca Strait. Cyclone Seed 95B formed extensive convective clouds, while Cyclone KOTO intensified rain clouds across western Indonesia by inducing wind shear and drawing moist air. This combined influence led to the severe rainfall and subsequent disasters.
Tropical Cyclone KOTO is a powerful tropical storm originating from a low-pressure system in the Sulu Sea, characterized by rapid intensification due to high sea surface temperatures. Classified as one of the most potent storms to approach Indonesian territory, it exhibited peak wind speeds similar to a strong tropical storm. BMKG also warned of potential moderate to heavy rainfall in other regions like West Kalimantan and Riau Islands, along with hazardous high waves across various marine areas due to KOTO’s broader influence.
