Blogs
Climate Bulletin for Sri Lanka (Week of 30 May – 06 June 2025)
Highlights
Rainfall Prediction: During the next week (21 May – 27 May), “fairly heavy” rainfall (50–100 mm) is predicted for the Central, Western,Uva, North-Western, and North-Central while “moderate” rainfall (25-50 mm) is expected in the Eastern, Southern, Sabaragamuwa, and Northern provinces.
Monitored Rainfall: Most days in May (21 April – 20 May) recorded above average rainfall, while the hydro catchment areas recorded an average of 12.8 mm per day. The highest daily rainfall was in Tabbowa on 17 May (128.9mm).
Monitored and Predicted Wind: From May 13 to May 19, winds at 850 mb (1.5 km) were from the North-West at speeds ranging between 6 – 10 m/s. From May 22 to May 28, Westerly winds are expected, with wind speeds ranging from 8 to 15 m/s.
Monitored Sea and Land Temperature: Over the past week, the maximum land surface temperature ranged from 30 °C to 35 °C. The temperature will remain above normal in some parts of the Northern and Eastern. The sea surface temperature around Sri Lanka ranged between below average 0.25°C and 1.0°C above average from 13 – 19 May 2025.
Interpretation
Monitoring
Rainfall: Most days over the month of May (28 April – 27 May) had above-average rainfall levels. Notably, 17th May recorded the highest daily average rainfall of 19 mm/day.
Wind: Westerly winds prevailed over the sea area and around the island last week, with wind speeds ranging between 10–15 m/s from 20-26 May.
Temperatures: Temperature anomalies were near-neutral across Sri Lanka from May 18 to 24.
Prediction
Rainfall: During the next week (28 May – 03 June), “fairly heavy” rainfall (50–100 mm) is predicted for the North-Western, Central, Sabaragamuwa and Western provinces, while “moderate” rainfall (25-50 mm) is expected in the North-central, Southern, Uva, Northern and Eastern provinces.
Temperatures: The temperature will remain above normal in some parts of the Northern, Eastern and and Southern provinces, with maximum temperatures reaching up to 37°C of Sri Lanka from 30 May to 05 June.
Teleconnections:The MJO will neutral rainfall from 28 May to 01 June, moderatly supress rainfall from 02 to 06 June, and significantly supress rainfall from 07 to 11 June.
Seasonal Precipitation: The precipitation forecast for the June-July-August 2025 season shows a 40% or more tendency toward above normal precipitation of Sri Lanka.
Terminology for Rainfall Ranges
| Terminology | Rainfall (mm/week) |
| Light Showers | Less than 12.5 mm |
| Light to Moderate | Between 12.5 mm and 25 mm |
| Moderate | Between 25 mm and 50 mm |
| Fairly Heavy | Between 50 mm and 100 mm |
| Heavy | Between 100 mm and 150 mm |
| Very Heavy | More than 150 mm |
