El Nino Watch

Samui metrics table and its colours

Rain is coloured by % of the 1991-2020 normal (orange under 75%, red under 60%, blue above 125%), heat by feels-like degrees and heat days, dry spells by length. The last row is the median of ENSO-neutral years, the yardstick.

Koh Samui watch

Each event's water year is reduced to six numbers for Koh Samui, all from the ERA5 grid cell that holds Maenam (ERA5 reanalysis):

  • Oct-Dec rain: the northeast-monsoon refill, as % of the 1991-2020 normal of the same cell.
  • Jan-May rain: the dry season after the El Nino peak.
  • Feb-Apr rain: the danger window when the tanks are lowest.
  • Max feels-like: the hottest daily maximum feels-like temperature in Jan-May, with its date.
  • Days >= 39 °C: days in Jan-May with a feels-like maximum at or above 39 °C (the risk engine's heat "watch" threshold, see Factor: extreme heat).
  • Longest dry spell: the longest run of days with less than 1 mm of rain in Jan-May, counted across month ends.

The neutral median row is the median of the same numbers over the water years whose ONI stayed between -0.5 and +0.5 °C from autumn to spring (no El Nino and no La Nina): what a "normal" year looks like in the same data. The count of years (n) is shown.

How to read it

Read down a column to compare events, and against the neutral row to see what is unusual. A cell shown as "--" with a "loading" note means a month of the ERA5 history is not stored yet; the number is not estimated.

Why it matters for Koh Samui

The Feb-Apr column is the one to watch: in 6 of the 7 events it was under 60% of normal, and that is the window when Samui ran short of water in 2016 and 2024.

Thresholds

ColourRain (% of normal)Meaning
redbelow 60%serious deficit: the live water factor calls this "prepare"
orange60% to 74%deficit: the live water factor calls this "watch"
plain75% to 125%near normal
blueabove 125%wet: the monsoon over-delivered (floods possible)

Heat cells go orange from 39 °C feels-like and red from 40 °C; heat days orange from 3, red from 7; dry spells orange from 30 days, red from 45. Thresholds match the live factors and the takeaways.

Sources

Related

ENSO status now

ONI (NOAA CPC)
+1.80 °C, JJA 2026 (previous +1.39 °C)
RONI (NOAA CPC)
+1.36 °C, JJA 2026
Nino 3.4 weekly (NOAA CPC / OISST)
+3.0 °C anomaly, week of 16 Sep 2026 (SST 29.6 °C)