Heavy rain could continue in parts of Sri Lanka until around 27 October, the Department of Meteorology said on Thursday, as the Irrigation Department warned of possible flooding along the Deduru Oya and the Kala Oya.
The department said the atmospheric disturbance near the island has developed into a low-pressure area, now located northwest of Sri Lanka and expected to move gradually westward. Rainfall above 100 millimetres is possible in parts of the Western, Sabaragamuwa, Central, North Western and Northern provinces, and in the Galle and Matara districts. Wet weather is expected to continue into 23 October.
The Irrigation Department said heavy rain in the upper and middle parts of the Deduru Oya basin has pushed the river close to flood level. Water is being released from the Deduru Oya Reservoir at about 16,500 cubic feet per second after its spill gates were opened, and the rate could rise depending on inflows. The department identified a flood risk in the lower river valley and low-lying areas of the Wariyapola, Nikaweratiya, Maho, Kobeigane, Bingiriya, Pallama, Chilaw, Arachchikattuwa and Rasnayakapura Divisional Secretariat Divisions.
On the Kala Oya, the spill gates of the Rajanganaya Reservoir have been opened, releasing more than 13,200 cubic feet per second (cusecs) into the river. The Irrigation Department said the discharge could increase in the coming hours. Areas at risk include the Rajanganaya, Nochchiyagama, Wanathawilluwa and Karuwalagaswewa Divisional Secretariat Divisions.
The Irrigation Department urged residents in both river basins to stay vigilant, and asked motorists and passengers to take extreme care on roads in the affected areas. It also asked disaster management authorities to take the necessary precautions.
Background
The Department of Meteorology said the Intertropical Convergence Zone, where winds from the Northern and Southern hemispheres meet, is positioned near Sri Lanka. It said this creates favourable conditions for cloud formation and further disturbances.
The department also said another low-pressure area could develop near the Andaman Islands around 23 October and strengthen into a depression over the Bay of Bengal. That system is not expected to affect Sri Lanka directly, but winds flowing towards it across the island could prolong rainfall, particularly in the south-west, until around 27 October.
October and November fall within the second inter-monsoon season, a period when thunderstorms and heavy afternoon showers are common in many parts of the island.
What it means
People living near the Deduru Oya and Kala Oya, and those travelling through the divisions named by the Irrigation Department, are advised to watch for further warnings as reservoir releases may change through the day.
The Meteorology Department asked fishing and naval communities, particularly crews of multiday vessels in the deep waters of the Bay of Bengal, to follow its forecasts. It also asked the public to take precautions against temporary strong winds and lightning during thundershowers. Winds of 60 to 70 kilometres per hour and very rough seas are possible during thundershowers. Residents with relatives in the affected provinces may wish to check on them and follow official updates.
