El Nino Watch
Uses the highest forecast feels-like temperature over the next 7 days, and how many days reach 41 °C, plus how much warmer than normal the last 30 days were.
Koh Samui watch
Main measure: the maximum daily feels-like (apparent) temperature forecast for the next 7 days (Open-Meteo), and the number of days at 41 °C or more.
It can also be raised by a persistent warm spell: if the daily maximum temperature over the last 30 days (ERA5) averaged 1.5 °C above normal, at least 1; 2.5 °C above normal, at least 2.
Why start at 39 °C: on Samui a feels-like of 32-38 °C is an ordinary day, so the thresholds are set higher than the "caution" bands.
Above 41 °C feels-like, heatstroke is possible, especially for children, older people and during exertion. Power cuts (no air conditioning) make it worse. El Nino makes March-May 2027 likely hotter than normal.
| Max feels-like (7-day forecast) | Factor level |
|---|---|
| below 39 °C | 0 Normal |
| 39 to 41 °C | 1 Watch |
| 41 °C or more on 1-2 days | 2 Prepare |
| 41 °C or more on 3+ days | 3 Act |
| 54 °C or more | 4 (counts as 3 in the overall level) |
Cap in the overall level: 3. Critical factor. Stale after 36 h without a forecast update. Heat >= 3 together with water >= 3 sets the overall level to 4 (rule R4b).