Vol. 1 No. 1 (2026): Journal of Earth and Planetary System Science

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.

Background: Climate change has affected rainfall patterns, particularly extreme rainfall events. As a region with high levels of tourism and socio-economic activity, the province of Bali is vulnerable to these changes. However, studies on trends in extreme rainfall in the Bali region remain limited.
Aims: This study aims to determine the trends and magnitude of changes in extreme rainfall indices (R20mm, RX1day, PRCPTOT, and CDD) in the Province of Bali during the period 1994–2023.
Methods: The data used consists of daily rainfall records from 17 BMKG stations, with a data completeness rate exceeding 90%. Extreme rainfall indices were calculated using the ETCCDI method. Trend analysis was conducted using the Mann-Kendall test and Sen’s Slope estimator. Additionally, monthly trend analysis was performed as a follow-up.
Result: The results indicate an increase in intensity-based extreme rainfall indices (RX1day, R20mm, and PRCPTOT), whilst the CDD index shows a decreasing trend. Several stations showed a significant upward trend, particularly in the PRCPTOT and RX1day indices. Monthly analysis also indicated increased rainfall in certain months, including the period from May to September.
Conclusion: These results highlight the importance of climate adaptation strategies and the mitigation of hydrometeorological disasters, particularly in the Bali region.