Sri Lanka alerted to 2.5 metre swells near shore
Swells of up to 2.5 metres are likely to occur off the coast of Puttalam to Galle via Colombo as a result of monsoonal westerly winds, Sri Lanka’s weather watchers said.
Squally weather with wind speeds of 60- 70 kilometres per hour is likely over the country, the Department of Meteorology said, while advising fishermen to stay onshore.
However, met officials said that the monsoon surge is expected to continue further and major bursts of the monsoon are likely during the weekend. They forecast moderate to heavy showers.
Shiromani Jayawardena of the department explained how the swells occurred last week.
“The southwest monsoon sets in over the extreme southwestern tip by the end of May. The onset of the monsoon is characterised by a sudden spurt of rainfall. It progresses inland in stages and covers the entire country by the middle of July.’’
Due to the monsoon, there are heavy winds. The ocean waves roll onto the shore not only due to heavy winds but because of swells.
Waves are most commonly caused by heavy wind and are created by the friction between wind and surface water. As the wind blows across the surface of the ocean, or a lake, the continual disturbance creates a wave crest.
Waves that reach a location as a swell can be up to 3 to 4 feet.
Longer period swells are between 15 to 20 seconds. Shorter period swells are less than 10 seconds. To get a long period swell, there needs to be strong winds that last a long time over a large body of water, the department explains.
That is what happened in the south. It is a combination of wind waves and swell waves. Not only the southwest monsoon.
The Natural Hazards Early Warning Center has issued amber warnings for land areas as strong winds of about 50- 60 km/ph can be expected at times over the western slopes of the Central hills, Western and Southern provinces due to the southwest monsoon.