Highlights

Predictions: From 27 May – 2 June, the US NOAA Climate Prediction Center predicts that the rainfall shall decrease across
SL. During this period, Western Plains & Hills are predicted to receive rainfall of 85-115 mm. From 28 May – 3 June, wind
speeds are predicted to be 8-15 m/s from the Northwest and West.
 
Monitoring: During the month of May, SL received nearly double the expected rainfall. However, relatively dry conditions were observed across the country during 21-26 May. During 21 – 26 May, the average daily rainfall was 5 mm. The highest daily rainfall was in Ratnapura – 197 mm, Katunayaka – 176 mm, Colombo – 100 mm on 21 May. From 19 – 25 May 2026, winds at 1.5 km elevation were mostly from the Northwest at 10 – 15 m/s. Overall the temperature was typical for May across SL. The Eastern Plains had an average maximum temperature of 34.8°C. The Eastern Hills had an average minimum temperature of 19.6°C.

Rainfall Prediction: From 27 May – 2 June, rainfall is predicted to decrease throughout SL: 85-115 mm is predicted for the Western Hills & Plains; 65-85 mm is predicted for the Southern Plains; 25-55 mm is predicted for the Northern Plains and Eastern Hills & Plains. From 3 – 9 June, rainfall shall increase: over 105- 125 mm is predicted for the Western Plains; 75- 105 mm rainfall for the Western Hills & Southern Plains. (Source: NOAA CPC)

Monitored Rainfall: During the month of May, SL received nearly double the expected rainfall. However, relatively dry conditions were observed across the country during 21-26 May. The highest daily rainfall was in Ratnapura – 197 mm, Katunayaka – 176 mm, Colombo – 100 mm on 21 May. During 20-26 May, the average daily rainfall was 5 mm.

Monitored Land & Sea Temperature: During 20-26 May, maximum average temp in SL was 32.0°C, higher compared to the previous week – 30.8°C. Western Hills had the lowest temperatures – 27.0°C. The sea surface temperature around SL was above the seasonal average by 1°C – 1.5°C around Western and Eastern coasts; by 0.25°C – 0.5°C around other coasts of SL.

Monitored & Predicted Wind: From 19 – 25 May 2026, winds at 1.5 km elevation were mostly from the West at 10 – 15 m/s. From 28 May – 3 June 2026, winds are predicted to speed up ( 8-15 m/s from the Northwest and West).



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