El Nino Watch
How hot it feels to the body, combining air temperature with humidity (and in some formulas wind and sun). In humid Samui it is often several degrees above the air temperature.
Koh Samui watch
Sweat cools you by evaporating. In humid air it evaporates slowly, so you feel hotter than the thermometer says. The "heat index" (US National Weather Service) and the "apparent temperature" (the Open-Meteo value used here, which also accounts for wind and solar radiation) both try to express this.
Heat index values assume shade. Full sunshine can add up to 8 °C (15 °F) according to the NWS.
Thai health and weather agencies use four heat index bands adapted from the NWS (table). The current NWS chart uses slightly lower upper bands (danger from 39.4 °C / 103 °F, extreme danger from 51.7 °C / 125 °F). This app's heat factor uses its own thresholds of 39, 41 and 54 °C (see Factor: extreme heat).
Heat is the most common El Nino hazard for people in Thailand. The risk is highest in March-May, during exertion, for older people and children, and during power cuts.
| Heat index (feels-like) | Band (TMD / Thai Department of Health) | Possible effects |
|---|---|---|
| 27 to 32 °C | Caution | Fatigue with prolonged exposure or activity |
| 32 to 41 °C | Extreme caution | Heat cramps, heat exhaustion or heat stroke possible with prolonged exposure or activity |
| 41 to 54 °C | Danger | Heat cramps or exhaustion likely; heat stroke possible |
| above 54 °C | Extreme danger | Heat stroke highly likely |