BMKG Warns of High Waves in North Sumatra Waters Until April 22
The Meteorology, Climatology, and Geophysics Agency (BMKG) has issued a warning for high waves in the waters off North Sumatra, Indonesia, affecting maritime activities and coastal communities through April 22. The alert comes as strong winds and shifting weather patterns generate dangerous sea conditions in the Malacca Strait and surrounding areas, prompting authorities to advise caution for fishermen, ferry operators, and recreational boaters.
According to BMKG’s latest marine weather bulletin, wave heights in the northern waters of Sumatra are expected to reach between 2.5 and 4.0 meters due to sustained winds of 20 to 25 knots from the north-northeast. These conditions are driven by a strengthening Asian monsoon surge interacting with localized atmospheric pressure gradients, which have intensified over the past 48 hours. The agency emphasized that the warning applies specifically to the waters off Aceh, North Sumatra, and parts of West Sumatra facing the Indian Ocean and the Malacca Strait.
“Fishermen and small vessel operators should avoid venturing out to sea during this period,” said Dwikorita Karnawati, Head of BMKG, in a public briefing on April 18. “We are monitoring the situation closely and will issue updates if conditions worsen or improve before the expected end date.” BMKG also urged port authorities in Belawan, Sabang, and Lhokseumawe to prepare for possible disruptions to cargo and passenger ship schedules.
The warning is part of BMKG’s routine marine hazard monitoring system, which uses satellite data, buoy measurements, and numerical weather modeling to forecast sea state conditions. High wave alerts are typically issued when wave heights exceed 2.5 meters, as such conditions increase the risk of capsizing, flooding of low-lying vessels, and difficulty in navigation — especially for traditional wooden boats commonly used by local fishers.
Indonesia’s National Search and Rescue Agency (Basarnas) has placed its teams on standby in coordination with BMKG, particularly in high-risk zones along the northern coastline. In recent years, similar wave events have led to multiple search-and-rescue operations, including incidents involving overloaded fishing boats and inter-island ferries caught in sudden squalls.
Maritime safety experts note that while high waves are a recurring seasonal phenomenon in the region — particularly during the transition between monsoons — climate variability may be contributing to more intense and unpredictable sea states. A 2023 study published in the Journal of Geophysical Research: Oceans found that rising sea surface temperatures in the eastern Indian Ocean have correlated with increased wave energy off Sumatra’s western coast during the boreal spring.
Local authorities in North Sumatra have begun disseminating BMKG’s advisories through community radio, mosque announcements, and WhatsApp networks used by fishing cooperatives. The provincial disaster management agency (BPBD) has also prepared evacuation routes and emergency shelters in low-lying coastal villages, though no flooding is currently expected from wave action alone.
BMKG advises the public to monitor real-time updates through its official website (bmkg.go.id), the BMKG mobile app, or via marine radio channels. The agency will continue to issue twice-daily marine forecasts until the warning period ends on April 22, after which conditions are expected to gradually improve as the monsoon surge weakens.
For those at sea, BMKG recommends checking wave forecasts before departure, ensuring life jackets are accessible, avoiding overloading vessels, and maintaining communication with coastal watch posts. In case of emergency, mariners are urged to contact Basarnas via the national distress number 115 or employ VHF Channel 16.
As Indonesia continues to grapple with the impacts of extreme weather on its vast archipelago, timely and accurate marine warnings remain critical to protecting lives and livelihoods dependent on the ocean. BMKG’s ongoing efforts to improve forecast precision and public outreach underscore the importance of integrating meteorological science with community-based safety practices.