BMKG Warns of Potential 4-Metre Waves in North Sumatra Waters

The Meteorology, Climatology and Geophysics Agency (BMKG) has reminded fishermen and other stakeholders to be alert to the potential for waves up to four metres high in several North Sumatra waters from 22 to 24 August 2026.

BMKG forecaster at the Class II Maritime Meteorology Station in Belawan, Dasmian Sulviani, said in Medan on Friday (21/8) that four-metre waves could potentially occur in the waters west of the Nias Islands, the Indian Ocean west of the Nias Islands, and the waters west of the Batu Islands.

Meanwhile, the waters west of North Sumatra, the Batu Islands waters, the waters east of the Nias Islands, and the waters east of North Sumatra could potentially experience waves of 1.25 to 2.5 metres.

In relation to these conditions, BMKG reminded fishermen using small boats to be alert to sea conditions when wind speeds reach 15 knots and wave heights reach 1.25 metres. Barge vessels also need to be alert when wind speeds reach 16 knots and wave heights reach 1.5 metres. Meanwhile, ferries need to increase vigilance when wind speeds reach 21 knots and wave heights reach 2.5 metres.

Dasmian said that wind deflection and warm sea surface temperatures in the western and eastern waters of northern Sumatra could increase evaporation potential, thereby contributing to the formation of rain clouds in the northern Sumatra region. Wind patterns in the area generally move from southeast to southwest with speeds of 4 to 25 knots.