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Climate Bulletin for Sri Lanka (Week of 17 October – 24 October 2025)
Highlights
Rainfall Prediction: From 14th-20th October, rainfall shall increase: high rainfall is predicted for the Western slopes and hills, Southern plains (105–135 mm), Eastern plains and hills are predicted to receive 75-105 mm while the Northern plains are predicted to receive 55-75 mm. From 21st-27th October, the rainfall shall intensify further with a similar spatial pattern.
Monitored Rainfall:During 7th-14th October, the average rainfall across Sri Lanka totalled 67 mm which was above–normal. Last week rainfall was high from 12th-14th of October. There was much higher rainfall across the Western slopes especially in Colombo and Ratmalana with a maximum of 155 mm on 14th October.
Monitored and Predicted Wind: From 29 September-05 October, winds at 1.5km height were mostly from the West at speeds ranging 6-15 m/s. From 08th-14th October, wind speeds are predicted to be high, in the range of 2-8 m/s still coming from the West and South West.
Monitored Sea and Land Temperature: From 06th -12th October, winds at 1.5 km height were mostly from the West and South West at speeds ranging 1-5 m/s. From 15th-21st October, wind speeds are predicted to be low, in the range of 1-3 m/s still coming from the West and South West.
Interpretation
Monitoring
Rainfall: Average Rainfall in the regions for the previous week of (08 October-14 October) = 9.6 mm/day. Maximum Daily Rainfall: 155.1 mm & Minimum Daily Rainfall: 0.0 mm.
Wind: Westerly and South Westerly winds prevailed over the sea area and around the island last week, with wind speeds ranging between 1-5 m/s from 06 – 12 Oct.
Temperatures:During the period 5 – 11 October, Sri Lanka experienced near-neutral conditions except in part of the Sabaragamuwa province.
Prediction
Rainfall: From 14– 20 October, rainfall is expected to be 105–135 mm/week in WP,WH and SP regions; 75-105 mm/week in EP and EH regions; 55-75mm/week in NP region.
Temperatures: From 16–29 October, Sri Lanka will experience moderate temperatures, ranging from 17°C to 33°C across the country (Source: SL Met Dept).
Teleconnections: The Madden-Julian-Oscillation (MJO) will slightly enhanced for rainfall from 13– 27 October.
Seasonal Precipitation: The forecast for the October-November-December 2025 season shows high tendency towards the near-neutral tercile despite the emerging La Nina (which lead to lower rainfall) however the temperature is predicted to have high chances of a warm anomaly.
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 |
