Background: Tropical cyclones forming within or near the Malacca Strait can trigger extreme rainfall over North Sumatra through interactions between cyclone dynamics, atmospheric moisture transport, and the orographic effects of the Bukit Barisan mountain range. However, the mechanisms linking Tropical Cyclone Senyar to remote orographic extreme rainfall remain poorly understood.
Aims: This study investigates the relationship between the structure of Tropical Cyclone Senyar and remote orographic extreme rainfall over North Sumatra.
Methods: ECMWF reanalysis data were processed using Python-based computational and visualization tools. The analyzed variables included total precipitation, 10-m zonal and meridional wind components, mean sea level pressure, specific humidity, and vertical velocity at 37 pressure levels. Topographic influences were represented using the 30-m SRTM Digital Elevation Model
Result: During 21–30 November 2025, Tropical Cyclone Senyar produced total rainfall accumulations of 117.16–871.48 mm (mean: 340.25 mm) and a maximum daily rainfall of 327.01 mm day⁻¹, with a minimum mean sea level pressure of 1009.64 hPa. Extreme rainfall (>150 mm day⁻¹) occurred mainly over Sibolga, North Tapanuli, Langkat, Medan, and Deli Serdang. Strong moisture transport, organized moisture flux corridors, localized moisture convergence, and persistent negative omega values at 500 hPa promoted deep convection. Rainfall maxima coincided with the orographic forcing zone along the Bukit Barisan range.
Conclusion: The integrated analysis demonstrates that Tropical Cyclone Senyar, moisture transport, vertical atmospheric dynamics, and orographic forcing acted synergistically to generate remote extreme rainfall over North Sumatra, providing new insights into extreme precipitation mechanisms in the equatorial maritime region.
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