Highlights

Cyclone Arnab

Cyclone Arnab began developing as a low-pressure area over the east-central and adjoining southeast Bay of Bengal on 23 October, approximately 1,200 km northeast of the Trincomalee coast, and intensified into a very severe cyclonic storm by 27 October. It made landfall along the Andhra Pradesh coast of India on 28 October, after moving away from Sri Lanka. However, its wind patterns influenced SL weather, increasing rainfall over the mountain slopes and the southwestern regions from 25-28 Oct.

Monitoring

Rainfall:During 20-26 Oct, there was extremely heavy rainfall in western, central, eastern and northern regions, with Mannar receiving the highest daily rainfall of 121 mm on 25 Oct. Highest average rainfall was in Western Plains – 27.9 mm and Northern Plains – 22.6 mm. Wind: From 28 Oct – 3 Nov 2026, winds are predicted to slow down to 1-4 m/s, arriving from the South-West and adjacent regions. Temperature: Overall, temperature was typical for October across SL, with Eastern Hills being relatively cooler (26.5°C). The warmest regions were Northern and Southern Plains with an average maximum temperature of 30.8°C. The coldest region at night was the Eastern Hills with an average minimum temperature of 19.4°C. 

Predictions

Rainfall: From 27 Oct – 2 Nov, the US NOAA Climate Prediction Center predicts that the SL shall receive fairly heavy rainfall between 45-95 mm. 75-95 mm is predicted for the western & eastern regions and less rainfall is predicted for northern and southern regions. During Nov-Jan, there is a 50% likelihood of SL receiving higher-than-normal tercile rainfall. Wind: From 28 Oct – 3 Nov 2026, winds are predicted to slow down to 1-4 m/s, arriving from the South-West and adjacent regions. The predictions for the coming week shows a dramatic slowing  down.

Indian Ocean (IO) SST

According to CCSR/IRI climate forecasts, there is 75-95% probability of a positive IOD from November through December 2026. The Dipole Mode Index (DMI) of the current positive IOD (Indian Ocean Dipole) phase has decreased to +0.69°C from +0.88°C last week. 

El Niño Event

El Niño conditions continue to prevail across the equatorial Pacific Ocean (Niño 3.4 region). Currently, sea surface temperature (SST) in the Niño 3.4 region is 3.3°C above average – this is one of the strongest El Nino events.

Rainfall Prediction

From 27 Oct–2 Nov, SL is predicted to receive fairly heavy rainfall of 45–95 mm. 75–95 mm is predicted for the Western Hills and Plains and Eastern Hills and Plains, while 45–75 mm is predicted for the Southern and Western Plains. From 2–9 Nov, 105–135 mm is predicted for the Western Hills, Western Plains and Eastern Plains. (Source: NOAA CPC)

Monitored Rainfall

During 20–26 Oct, there was extremely heavy rainfall in the Western, Central, Eastern and Northern regions, with Mannar recording the highest daily rainfall of 121 mm on 25 Oct. The highest average rainfall was recorded in the Western Plains (27.9 mm) and Northern Plains (22.6 mm). During 21–27 Oct, the average daily rainfall across SL was 18.7 mm.

Monitored Land & Sea Temperature

Overall, temperature was typical for October across SL, with the Eastern Hills being relatively cooler (26.5°C). During 21–27 Oct, the average maximum temperature in SL was 30.2°C, lower than the previous week’s average of 31.2°C. The sea surface temperature around SL was 1.5–2.0°C warmer than the seasonal average around the Western coasts and 0.5–1.5°C warmer around the rest of the coasts.

Monitored & Predicted Wind

The winds during the last week were from the South-West at high speeds. Predictions for the coming week show a dramatic decrease in wind speeds. From 19–25 Oct 2026, winds at 1.5 km elevation were from the South-West and adjacent regions, at speeds of 4–8 m/s. From 28 Oct–3 Nov 2026, winds are predicted to slow down to 1–4 m/s, continuing to arrive from the South-West and adjacent regions.