Blogs
Climate Bulletin for Sri Lanka (Week of 12 September – 19 September 2025)
Highlights
Rainfall Prediction: Sri Lanka is reaching the peak of its dry season Moderate rainfall (15–25mm) is expected in parts of Central, Sabaragamuwa, Uva, Western, Southern, Eastern, and North Western provinces during 09–15 September. Light rainfall (5–15mm) may occur in districts of North Western, Southern, North Central, Eastern, and Northern provinces.
Monitored Rainfall: The 30 day cumulative rainfall till 9th September shows that rainfall totaled about 37mm whereas the expected rainfall was 70mm. During 02-09 September, Sri Lanka received an average rainfall of 2.7 mm/day, while in the hydro catchments, the average rainfall was 4.7 mm/day
Monitored and Predicted Wind: From 01-07 September, winds at 1.5 km height was mostly from the North-West at speeds ranged 8-10 m/s. From 10-16 September, wind speeds are predicted to range between 4-10 m/s coming from the North-West.
Monitored Sea and Land Temperature: Average maximum land surface temperature was 32.9 °C during 02-09 September. The Eastern Plains were the warmest, followed by Southern and Northern Plains. The sea surface temperature was near-neutral around the Western, Eastern, and Southern coasts, while it was warmer around the Northern and South-Western coasts, ranging between 0.5 °C and 1 °C above average.
Interpretation
Monitoring
Rainfall: Average Rainfall in the regions for the previous week of (02 September-09 September) = 2.7 mm/day. Maximum Daily Rainfall: 69.1 mm & Minimum Daily Rainfall: 0.0 mm.
Wind: North-Westerly winds prevailed over the sea area and around the island last week, with wind speeds ranging between 8-15 m/s from 01-07 September.
Temperatures: From August 31 to September 6, Sri Lanka experienced above-normal temperature anomalies, except in Northern, North-Central (some areas), North-Western (some areas), and parts of the Central and Eastern provinces.
Prediction
Rainfall: During the next week, 15-25 mm/week rainfall is expected for Central province, Kegalle, Badulla, Gampaha, Colombo, Kalutara, Matara, Monaragala, Ratnapura, Ampara, Batticaloa, and Kurunegala, Puttalam, Galle, Hambantota districts, while 5-15 mm/week rainfall is predicted for Polonnaruwa, Anuradhapura, Trincomalee, Vauniya, Mannar, Mullativu, Kilinochchi and Jaffna districts.
Temperatures: The temperature will remain above normal in some parts of the Northern, North-Central, Uva, Southern, Eastern and North-Western provinces and in Matale with maximum temperatures reaching between 34°C and 38°C of Sri Lanka from 11 September – 24 September.
Teleconnections: The MJO will moderately enhance rainfall from September 9–13, slightly enhance rainfall from September 14–18, and remain near-neutral from September 18–23.
Seasonal Precipitation: The precipitation forecast for the September-October-November 2025 season shows a 45% of tendency below normal in the Northern province of Sri Lanka and 50% of tendancy below normal in the rest of the provinces.
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 |
