Blogs
Climate Bulletin for Sri Lanka (Week of 23- 30 May 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 in May (21 April – 20 May) recorded above average rainfall. The highest daily rainfall was in Tabbowa on 17 May (128.9mm).
Wind: North-Westerly winds prevailed over the sea area and around the island last week, with wind speeds ranging between 6–10 m/s from 13 – 19 May.
Temperatures: Temperature anomalies were above average in the Southern and North-Western Provinces, while near-neutral in other parts of Sri Lanka from 11 to 17 May.
Prediction
Rainfall: 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.
Temperatures: The temperature will remain above normal in some parts of the Northern, and Eastern with maximum temperatures reaching up to 34°C of Sri Lanka from May 23 to May 31.
Teleconnections: The MJO will slightly enhance rainfall from May 20 to May 29, and neutral rainfall from May 30 to 03 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 |
