Highlights

Predictions: From 19 – 25 May, the US NOAA Climate Prediction Center predicts that the rainfall shall increase across SL. During this period, Western Plains are predicted to receive rainfall of 105-135 mm. From 20 – 26 May, wind speeds are predicted to be 5-10 m/s from the Northwest.
 
Monitoring: A Low Pressure Area (LPA) developed over the Bay of Bengal (BoB) on 10th May, with wind speeds ranging from 20-30 m/s. The LPA remained over the Southwest of BoB until 14th May. This caused the rainfall across SL to increase. During 13 – 19 May, the average daily rainfall was 31 mm. The highest daily rainfall was in Puttalam – 256 mm on 13 May, Colombo – 98 mm on 14 May, Batticaloa – 95 mm on 14 May. From 11 – 17 May 2026, winds at 1.5 km elevation were mostly from the Northwest at 5 – 10 m/s. Overall the temperature was typical for May across SL. The Eastern Plains had an average maximum temperature of 33.2°C. The Eastern Hills had an average minimum temperature of 19.6°C.
 

Rainfall Prediction: From 19 – 25 May, rainfall is predicted to increase throughout SL: 105-135 mm is predicted for the Western Plains; 85-105 mm is predicted for the Western Hills; 25-55 mm is predicted for the Southern Plains, Northern Plains and Eastern Hills & Plains. From 26 May – 1 June, rainfall shall increase: over 135 mm is predicted for the Western Plains & Hills; 45-105 mm rainfall for the rest of SL. (Source: NOAA CPC)

Monitored Rainfall: Due to the Low Pressure Area (LPA) that affected SL from 10-14 May, Western Plains and Eastern Hills experienced heavy rainfall. The highest daily rainfall was in Puttalam – 256 mm on 13 May, Colombo – 98 mm on 14 May, Batticaloa – 95 mm on 14 May.
During 13-19 May, the average daily rainfall was 31 mm.

 

Monitored Land & Sea Temperature: During 13-19 May, maximum average temp in SL was 30.8°C, lower compared to the previous week – 31.6°C.Western Hills had the lowest temperatures – 26.6°C.Eastern Plains had the highest temperatures – 33.2°C The sea surface temperature around SL was above the seasonal average by 0.5°C – 1.0°C.

 

Monitored & Predicted Wind: From 11 – 17 May 2026, winds at 1.5 km elevation were mostly from the Northwest at 5 – 10 m/s. From 20 – 26 May 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