Extreme Rainfall from Tropical Cyclone Senyar Triggers Widespread Flooding and Infrastructure Damage Across Aceh (November 25 – 26, 2025)
Rainfall associated with tropical disturbances typically contributes to the replenishment of water resources across Southeast Asia. However, in late November 2025, the early development of Tropical Cyclone Senyar (34W) over the Strait of Malacca produced rainfall far exceeding the absorptive capacity of the region. Within a 24-hour period, Aceh experienced one of its most intense rainfall episodes in recent years, resulting in widespread flooding, landslides, and substantial damage to critical infrastructure.
Between 25 and 26 November 2025, hydrological observations from 173 monitoring stations across Aceh recorded heavy to extreme rainfall, based on data from the Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG). The most pronounced rainfall totals were documented at Kuala Subdistrict, Bireuen Regency (411 mm); Karang Baru, Aceh Tamiang Regency (397.4 mm); Langsa Baro, Langsa City (382 mm); Pasie Raja, South Aceh Regency (376.6 mm); and Meureudu, Pidie Jaya Regency (376.6 mm).
Satellite-based estimates derived from NASA’s Global Precipitation Measurement (GPM) mission—specifically the Integrated Multi-Satellite Retrievals for GPM (IMERG) product—corroborated the spatial extent and severity of the event. The IMERG rainfall composite for 25–26 November indicates elevated mean rainfall values across large parts of Aceh, with dark-red regions representing average accumulations exceeding 400 mm. These satellite-detected rainfall maxima align closely with BMKG’s ground measurements, although localized convective bursts produced higher totals at certain stations than what satellites were able to resolve due to temporal averaging.
The event was influenced by the initial formation of Tropical Cyclone Senyar on 21 November, which remained quasi-stationary over the Strait of Malacca while channelling substantial moisture toward northern Sumatra. Persistent moisture convergence, combined with saturated soil conditions from recurrent rainfall in preceding weeks, greatly increased the likelihood of rapid-onset flooding. As rivers exceeded their capacities, overbank flow quickly inundated low-lying areas.
The hydrological impacts were considerable. Several major bridges and road segments suffered structural failure or were rendered inaccessible, including sections of the Banda Aceh–Medan national route, a key transportation corridor connecting northern Aceh with the rest of Sumatra. Fast-moving floodwaters undermined road foundations and washed away pavement, isolating multiple communities.
The situation was further compounded by extensive power outages. Electrical supply was disrupted for more than 24 hours across numerous districts, and at the time of reporting, several areas remained without power due to damage to transmission lines caused by flooding and landslides. These cascading failures contributed to the displacement of thousands of residents, widespread inundation of residential zones, and interruptions to essential public services. In coastal regions, strong winds and moderate-to-high waves associated with the developing cyclone intensified local impacts.
Ongoing scientific assessments are examining the interactions between tropical disturbances in the Indian Ocean and regional rainfall variability in western Indonesia. Extreme events such as this underscore the importance of strengthened hydrometeorological monitoring, improved early-warning capabilities, and enhanced community preparedness in regions highly susceptible to rapid-onset flooding.
Map of Average Rainfall by TDMRC -USK, using IMERG data from the Global Precipitation Mission (GPM) at NASA/GSFC. Written by Saumi Syahreza.
References & Resources
Badan Meteorologi, Klimatologi, dan Geofisika (BMKG). Peringatan Dini Cuaca Ekstrem Aceh. Accessed November 28, 2025.
European Centre for Medium-Range Weather Forecasts (ECMWF). ERA5 Reanalysis Data. Accessed November 28, 2025.z
Zoom Earth. Tropical Storm 34W (Senyar) – Satellite and Wind Analysis. Accessed November 28, 2025.
Badan Penanggulangan Bencana Aceh (BPBA). Banjir di 16 Kabupaten/Kota Provinsi Aceh per 27 November: 20.759 Jiwa Mengungsi, Satu Orang Hilang. Accessed November 28, 2025.
