El Nino Watch

Koh Samui El Nino Risk Watch: Drought, Heat, Storms

Koh Samui (Thailand) El Nino risk level today: water supply, rain vs normal, heat, flood, cyclone, sea state, air quality and coral heat stress, with sources.

Level: Prepare

Prepare -- strong El Nino (ONI +1.80 °C JJA 2026; RONI +1.36 °C; Nino 3.4 +3.0 °C week of 16 Sep). No immediate threat on Samui: rain 108% of normal (90 d to 19 Sep), waves max 0.6 m (forecast to Sun 27 Sep), no cyclone within 800 km (nearest 1,997 km). Watch: heavy rain / flood -- TMD heavy-rain bulletin 225/2569 for the South, in force to Sun 27 Sep (forecast 25 mm over 3 days). Next risk: NE-monsoon heavy rain and rough seas Oct-Dec 2026 (November wettest); water stress Feb-Apr 2027.

Evaluated 25 Sep 2026 14:15 UTC for Maenam, Koh Samui.

Factors

FactorLevelValueThresholdAs ofSource
El Nino (event strength)prepare+3.0 °C (Nino 3.4, week of 16 Sep)RONI/ONI or weekly Nino 3.4 >= +0.5 °C watch, >= +1.5 °C (strong) prepare16 Sep 2026 00:00 UTCNOAA CPC (RONI, ONI, Nino 3.4) + IRI
Rain deficit / water shortagenormal108% of normal (22 Jun-19 Sep: 303 mm vs 282 mm normal)90 d (180 d in the dry season) < 75% watch, < 60% prepare, < 40% and >= 100 mm short act; PWA notice watch, > 48 h prepare; + confirmed shortage = 419 Sep 2026 00:00 UTCOpen-Meteo ERA5 vs 1991-2020 ERA5 normal, ECMWF SEAS5, PWA, ThaiWater
Extreme heatnormal37.5 °C feels-like, forecast for Thu 1 Oct>= 39 °C watch, >= 41 °C (danger) prepare, 3 days >= 41 °C act, >= 54 °C leave; or 30-day Tmax >= +1.5 / +2.5 °C25 Sep 2026 13:21 UTCOpen-Meteo (forecast) + ERA5
Heavy rain / floodingvigilance16 mm on Sat 26 Sep (forecast wettest day; 25 mm over 3 days)TMD: 35.1-90 mm heavy, > 90 mm very heavy in 24 h; 72 h >= 100/150/250 mm; +1 level if the past 7 days >= 150 mm25 Sep 2026 13:21 UTCOpen-Meteo, ThaiWater (HII/TMD), TMD
Tropical cyclone / windnormal56 km/h max gust, forecast for Sun 27 Sep; no cyclone within 800 kmcyclone <= 800 km watch, orange/red <= 800 km prepare, <= 300 km act, orange/red <= 300 km leave; gusts >= 75/89/118 km/h25 Sep 2026 13:21 UTCGDACS, JTWC/JMA/EONET positions, Open-Meteo, TMD
Sea state (ferries, isolation)normal0.6 m, forecast max on Sun 27 Sep1.5 m watch, 2 m prepare (small boats stay in port), 3 m act25 Sep 2026 13:22 UTCOpen-Meteo Marine
Air quality (PM2.5, haze)normal6.8 µg/m³ PM2.5 (observed, at Environment Agency Section 14, Surat Thani)PCD 24 h PM2.5: > 37.5 µg/m³ watch, > 75 prepare, > 125 act25 Sep 2026 10:00 UTCPCD Air4Thai (measured) + Copernicus CAMS (model)
Marine heat / coral bleachingnormal0.0 °C-weeks (West Gulf of Thailand, 23 Sep)CRW: DHW >= 4 °C-weeks Alert 1, >= 8 Alert 223 Sep 2026 00:00 UTCNOAA Coral Reef Watch
Media / social signal (Samui, Thailand)vigilance2 Samui items in 14 days>= 3 Samui mentions or >= 10 Thailand: watch (capped at 1)25 Sep 2026 14:15 UTCThe app's news/social feeds

What to do now

  • Build 14 days of self-sufficiency: water, no-cook food, medication (30 days).
  • Fill and clean the cistern; fit a filter and keep purification tablets.
  • Charge power banks, headlamps, batteries; test the generator/solar panel.
  • Mosquito nets and repellent: dengue rises with heat and rain.
  • Copies of documents (passport, visa, insurance) in a waterproof bag + online.
  • Decide your departure threshold in advance (e.g. water cut for more than 3 days).
  • Strong El Nino: prepare for the 2027 dry season now (cistern, water stock, a plan if ferries stop).
  • Keep documents and electronics high and dry, avoid flooded roads and slopes (landslides), never cross moving water.
  • Check local information (Samui groups, PWA, municipality) before acting.

What would raise the level

  • Rain deficit / water shortage: 90-day rain < 40% of normal (>= 100 mm short)
  • Extreme heat: 3 days >= 41 °C
  • Heavy rain / flooding: >= 150 mm in 24 h or 250 mm in 72 h
  • Tropical cyclone / wind: cyclone within 300 km
  • Sea state (ferries, isolation): waves >= 3 m
  • Air quality (PM2.5, haze): PM2.5 > 125 µg/m³
  • Two physical hazards at 'prepare' at the same time (e.g. heavy rain + 2 m seas).

ENSO context

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)
NOAA CPC ENSO status
El Niño Advisory (issued 10 Sep 2026), El Niño is strengthening, with a greater than 90% chance of a very strong event during the Northern Hemisphere fall and winter 2026-27. source