NOAA has an El Nino Advisory in force. In September 2026 it gave a greater than 90% chance of a very strong event in late 2026 and early 2027.
El Nino basics
What NOAA's Climate Prediction Center said in its 10 September 2026 discussion:
ENSO Alert System status: El Nino Advisory.
El Nino strengthened in August, with surface anomalies above +3.0 °C in the eastern equatorial Pacific. Nino 3.4 reached +1.8 °C, Nino 3 +2.5 °C and Nino 1+2 +3.4 °C (Nino 4 only +0.1 °C).
Subsurface anomalies exceeded +10 °C at depth; the thermocline is deeper than average.
Rain is enhanced from the central to the eastern Pacific and suppressed over Indonesia.
For October-December 2026, a 75% chance of a historic event, stronger than any since 1950 (3-month RONI of +2.5 °C or more).
Overall: more than 90% chance of a very strong event during the northern fall and winter 2026-27.
The 3-month values published by the CPC for June-August 2026: ONI +1.80 °C, RONI +1.36 °C. The app shows the newest values on the Overview and Indices pages.
Why it matters for Koh Samui
A very strong El Nino peaking around the end of 2026 raises the odds of a drier, hotter February-April 2027 on Samui, on top of a water system that was already rationed in August 2026.