Blogs
Climate Bulletin for Sri Lanka (Week of 05 September – 12 September 2025)
Highlights
Rainfall Prediction: Sri Lanka is reaching the peak of its dry season Moderate rainfall of 15–25 mm is expected in the Central province during 02–08 September, light rainfall of 5–15 mm rainfall may occur in surrounding districts. Other regions are likely to experience very little rain or remain dry.
Monitored Rainfall: During 26 August-02 September, Sri Lanka received an average rainfall of 1 mm/day, while in the hydro catchments, the average rainfall was 5.6 mm/day. The 30 day cumulative rainfall till 1st September shows that rainfall totaled about 30 mm whereas the expected rainfall was 75mm.
Monitored and Predicted Wind: From 25-31 August, winds at 1.5 km height was mostly from the North-West at speeds ranged 8-15 m/s. From 03-09 September, wind speeds are predicted to range between 4-8 m/s coming from the West.
Monitored Sea and Land Temperature: Average maximum land surface temperature was 32.8 °C during 26 August-02 September. The Eastern Plains were the warmest, followed by Southern and Northern Plains. From 25-31 August, the sea surface temperature is ranging between 0.25 °C to 0.5 °C above-average levels around Southern coast while it is warmer around the Northern, Western and Eastern coasts, ranging between 0.5 °C to 1.5 °C above-average levels.
Interpretation
Monitoring
Rainfall: Average Rainfall in the regions for the previous week of (26 August-02 September) = 1.1 mm/day. Maximum Daily Rainfall: 35.7 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 25-31 August.
Temperatures: Temperature anomalies were above-normal for Sri Lanka except for Northern, North-Central, North-Eastern provinces and some parts in Central, Eastern and Western provinces from August 24 to 30.
Prediction
Rainfall: During the next week, 15-25 mm/week rainfall is expected for Central province, while 5-15 mm/week rainfall is predicted for Badulla, Kegalle districts, while 0-5 mm/week rainfall is predicted for the Northern, Eastern, North-Central, Western, North-Western, Southern provinces and Moneragala, Ratnapura districts.
Temperatures: The temperature will remain above normal in some parts of the Northern, North-Central, Eastern and North-Western provinces and in Matale with maximum temperatures reaching between 34°C and 39°C of Sri Lanka from 03 September – 18 September.
Teleconnections: The MJO will be near-neutral from 02-16 September. A brief period of La Niña conditions has higher probabilities in the coming months. The Indo-Pacific rainfall predictions show La Nina type anomalies.
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 |
