Highlights

Predictions: From 12 – 18 May, the US NOAA Climate Prediction Center predicts that the rainfall shall increase across SL. During this period, Western Hills & Plains are predicted to receive rainfall over 105-135 mm. From 13 – 19 May, wind speeds are predicted to be 6-10 m/s.
 
Monitoring: A Low Pressure Area (LPA) developed over the Bay of Bengal (BoB) on 10th May, with wind speed ranging from 20-30 m/s. The LPA remained over the southwest of Bay of Bengal until 12th May. This caused the rainfall across SL to increase. During 6 – 12 May, the average daily rainfall was 14 mm. The highest daily rainfall was in in Ratmalana – 202 mm on 12 May, Ratnapura – 131 mm on 12 May, Katunayaka – 94 mm on 8 May, Puttalam – 89 mm on 11 May. During 4 – 10 May, winds were from Northwest with 2–5 m/s. Overall, the temperature was typical for May across SL. The Eastern Plains had an average maximum temperature of 32.9°C. The Eastern Hills had an average minimum temperature of 19.2°C.
 

Rainfall Prediction: From 12 – 18 May, rainfall is predicted to increase throughout SL: 105-135 mm is predicted for the Western Hills & Plains; 55-105 mm is predicted for the Southern Plains, Eastern Hills & Plains; 45-55 mm is predicted for the Northern Plains. From 19 – 25 May, rainfall shall decrease: 105-125 mm is predicted for the Western Plains and 45-105 mm rainfall for the rest of SL. (Source: NOAA CPC)

Monitored Rainfall: The low pressure area developed over the southwest of Bay of Bengal caused the rainfall to increase across Sri Lanka. During 6 – 12 May, the average daily rainfall was 14 mm. The highest daily rainfall was in Ratmalana – 202 mm on 12 May, Ratnapura – 131 mm on 12 May, Katunayaka – 94 mm on 8 May, Puttalam – 89 mm on 11 May.

 

Monitored Land & Sea Temperature: During 6 – 12 May, maximum average temp in SL was 31.6°C, lower compared to the previous week – 33.0°C. Eastern Hills had the lowest temperatures – 27.7°C. The sea surface temperature around northern and western coasts was above the seasonal average by 1°C – 1.5°C while it was 0.5°C – 1.0°C around other coasts.
 

Monitored & Predicted Wind: From 4 – 10 May 2026, winds at 1.5 km elevation were mostly from the Northwest at 2 – 5 m/s. From 13 – 19 May 2026, winds are predicted to speed up ( 6-10 m/s from the Northwest and Southwest).



Terminology for Rainfall Ranges

TerminologyRainfall (mm/week)
Light ShowersLess than 12.5 mm
Light to ModerateBetween 12.5 mm and 25 mm
ModerateBetween 25 mm and 50 mm
Fairly HeavyBetween 50 mm and 100 mm
HeavyBetween 100 mm and 150 mm
Very HeavyMore than 150 mm