The Department of Meteorology has issued an “Amber” advisory for high waves in the sea areas extending from Negombo to Pottuvil via Galle, Matara and Hambantota.
Swell waves of about 2.5 to 3.0 metres in height may increase in those waters, the department said.
It added that near-shore sea areas off the coast extending from Beruwala to Matara via Galle may experience surges caused by the swell.
Naval and fishing communities operating in the affected sea areas have been asked to remain vigilant.
A different hazard from the wind advisories
The bulletin is a swell-wave warning rather than a wind warning, which distinguishes it from the run of Amber advisories the department has issued this month.
Those earlier bulletins were issued for strong winds and rough seas, with gusts forecast at 55-60 kmph across the Matara-to-Pottuvil and Kankesanturai-to-Chilaw stretches, and followed a similar advisory two days earlier that put gusts at 50 kmph.
Swell waves travel out of distant weather systems and can arrive in calm local conditions, which is why the department separates them from wind-driven rough seas. The stretch named on Tuesday runs down the west coast and around the south, covering Colombo, Galle, Matara and Hambantota before turning north to Pottuvil.
What Amber requires
The Amber band asks communities working in the affected waters to be vigilant and take precautions. It stops short of the Red level, at which fishing and naval communities are instructed not to venture into the affected areas at all — the step the department took in an advisory issued on August 8, when gusts of 60-70 kmph were forecast.
The department did not state an expiry time for the advisory, and asked those affected to follow subsequent forecasts.
Marine warnings have recurred through August around the island. The bulletin sits alongside a separate warm weather advisory covering the Eastern Province and six northern and eastern districts, issued the same afternoon.
No newsroom other than Ada Derana carried the advisory at the time of writing.
Update — reissued August 20
The Met Department has kept the advisory running, reissuing it on Thursday with the same wave heights and the same near-shore surge warning for Beruwala to Matara via Galle.
Only the northern boundary of the affected stretch has moved. Tuesday’s bulletin ran from Negombo, Wednesday’s from Puttalam, and Thursday’s from Chilaw — in each case south and east to Pottuvil via Galle, Matara and Hambantota. The swell forecast has held at 2.5 to 3.0 metres throughout, and the department has continued to ask naval and fishing communities in those waters to remain vigilant.
