BMKG: Alert for 4-metre waves in North Sumatra waters until 14 September

Four-metre high waves may occur in the waters west of the Nias Islands, the waters west of the Batu Islands, and the waters east of the Nars Islands.

Medan (ANTARA) - The Meteorology, Climatology, and Geophysics Agency (BMKG) has stated that several waters in North Sumatra are at risk of being hit by waves as high as four metres due to strong winds from 11 to 14 September 2026.

“Waves as high as four metres may occur in the waters west of the Nias Islands, the waters west of the Batu Islands, and the waters east of the Nias Islands,” said BMKG Forecaster at the Class II Maritime Meteorology Station Belawan, Dasmian Sulviani, in Medan on Friday.

She stated that wind shifts in the northern Sumatra region, combined with warm sea surface temperatures in the Indian Ocean west of Sumatra, could support the formation of convective clouds in the northern Sumatra area.

The wind pattern generally moves from the southeast to the southwest, with wind speeds ranging between 10 and 25 knots.

Consequently, the BMKG advises fishermen using boats to remain alert if wind speeds reach 15 knots and wave heights reach 1.25 metres. Barge vessels are advised to be cautious if wind speeds reach 16 knots and wave heights reach 1.5 metres, while ferry operators should be alert if wind speeds reach 21 knots and wave heights reach 2.5 metres.

According to monitoring results of Hotspot distribution imagery in North Sumatra on 10 September 2026, there were nine hotspots with moderate confidence levels scattered across Mandailing Natal, North Padang Lawas, and North Tapanuli Regencies.

Observations from the Silangit, F.L. Tobing Sibolga, and Aek Godang Meteorology Stations indicate that from 11 September 2026 until 11:00 WIB, visibility in these areas ranges between 5 km and 10 km.

Monitoring of air quality regarding PM2.5 concentrations (very fine particulate matter) in North Sumatra remains in the good category.