Past El Ninos on Koh Samui: 1982 to 2024 vs 2026-27

The ERA5 history behind this page

921 months from 1950-01 to 2026-09, ERA5 through 2026-09-18 (Open-Meteo archive, updated 25 Sep 2026 13:36 UTC).

Takeaways

1. In 6 of 7 strong El Ninos, Samui's Feb-Apr rain was below 60% of the 1991-2020 normal (1982-83, 1991-92, 1997-98, 2009-10, 2015-16, 2023-24); the neutral-year median is 66% (n=18).
2. Jan-May rain (the dry season after the peak) was below 75% of normal in 6 of 7 events (1982-83, 1991-92, 1997-98, 2009-10, 2015-16, 2023-24): event median 55% vs 82% in neutral years.
3. The Oct-Dec refill (NE monsoon) was below 80% of normal in 3 of 7 events (1991-92, 1997-98, 2009-10); event median 91% vs 92.5% in neutral years: a strong El Nino does not guarantee a weak monsoon on the Gulf coast.
4. Dry-season heat: max feels-like reached 40.3 °C in 2023-24 (on 2024-05-27); event median 39.4 °C vs 37.7 °C in neutral years (ERA5 cell values, cooler than a Samui thermometer).
5. Days at or above 39 °C feels-like in Jan-May: event median 1 vs neutral median 0; the most was 11 in 2023-24.
6. Longest dry spell (days under 1 mm) in Jan-May: event median 28 days vs 23 in neutral years; longest 50 days in 1997-98.
7. At the same stage (JJA), ONI +1.80 °C in 2026 is above 7 of 7 analogs (1997-98 +1.48, 2015-16 +1.44, 1987-88 +1.30 were the highest); the 2026 event started early and fast.
8. So far in 2026 (Jun-Aug 2026, the complete months; ERA5 through 2026-09-18): 254 mm = 96% of the normal for those months; the decisive months (the Oct-Dec refill, then Feb-Apr 2027) are still ahead.
9. Sample: 7 events and 18 neutral years from one ~30 km ERA5 grid cell; each El Nino differs and the climate has warmed since 1982, so use these as ranges, not forecasts.

Seven strong El Ninos vs 2026-27 (ERA5 cell, % of the 1991-2020 normal)

48 documented impacts (each checked at its link)

• 2026-07-29 (water_shortage, Koh Samui): Dry weather worsened by El Nino depleted Samui's reservoirs in July 2026: the undersea pipeline from the mainland supplies about 16,000 m³ a day against an average demand of about 34,000 m³, so the PWA rotated tap water supply across zones of the island from 3 August 2026; hotels bought trucked water and the Interior Ministry ordered urgent measures. Bangkok Post -- Koh Samui faces water rationing [strong El Nino 2026-27 (the current event, developing year)]
• 2025 (paper, Thailand (rainfall vs ENSO and IOD)): Madolli M.J. et al. (2025), A systematic review on rainfall patterns of Thailand: insights into variability and its relationship with ENSO and IOD, Earth-Science Reviews. Earth-Science Reviews -- A systematic review on rainfall patterns of Thailand [context]
• 2024-12-28 (flood, Koh Phangan (Surat Thani)): All-night rain to the morning of 28 December 2024 flooded residential areas and roads on Koh Phangan; a pickup truck was swept into the sea near Ban Tai. Thai Newsroom -- Koh Phangan flooded after heavy all-night rain [ENSO-neutral, the winter after the 2023-24 El Nino]
• 2024-12-14 (flood, Koh Tao (Surat Thani)): Flash floods up to 60 cm deep hit Koh Tao on 14 December 2024 after continuous heavy rain since 13 December, damaging homes, shops, motorcycles and cars. Thai FYI -- Flash floods hit Koh Tao following heavy rainfall [ENSO-neutral, the winter after the 2023-24 El Nino]
• 2024-12-04 (flood, southern Thailand (Pattani, Narathiwat, Songkhla, Nakhon Si Thammarat, Phatthalung)): The death toll reached 29 by 4 December 2024, with more than 155,000 households affected and over 33,000 people displaced; the cabinet approved relief payments. VOA -- Death toll rises to 29 in southern Thailand floods [ENSO-neutral, the winter after the 2023-24 El Nino]
• 2024-11-30 (flood, southern Thailand (8 provinces; Surat Thani among relief recipients)): By 30 November 2024 the southern floods had killed 9 (Phatthalung 1, Songkhla 3, Pattani 3, Yala 1, Narathiwat 1) and affected over 550,000 people in 78 districts; 200 shelters held more than 13,000 evacuees; Surat Thani was among six provinces allotted 70 million baht each in relief. Khaosod English -- Southern Thailand flooding crisis worsens: 9 dead, over 550,000 affected [ENSO-neutral, the winter after the 2023-24 El Nino]
• 2024-11-30 (flood, southern Thailand (Nakhon Si Thammarat to Satun)): At least 4 dead and more than 240,000 households affected by 30 November 2024; 24-hour rainfall reached 205 mm at Chian Yai (Nakhon Si Thammarat) and 128.2 mm at Khao Chong (Trang). Surat Thani is not listed in this report. The Watchers -- Severe floods hit southern Thailand, affecting over 240 000 households [ENSO-neutral, the winter after the 2023-24 El Nino]
• 2024-05-25 (bleaching, Thailand (21 marine national parks, 9 in the Gulf)): By late May 2024 the DNP had detected coral bleaching at 152 locations in 21 marine national parks, nine of them in the Gulf of Thailand: 54 sites with extremely severe bleaching (over 50%), 56 severe (11-50%), 39 medium (1-10%); dive sites in five parks were closed from 2 April. Bangkok Post -- Bleaching forces diving site closures [strong El Nino 2023-24 (sea warming after the peak)]
• 2024-05-13 (bleaching, Thai marine parks (6 Gulf, 6 Andaman)): Twelve marine parks were under watch from early April 2024; three showed 50-80% bleaching in water under 2 m, described as part of the fourth global bleaching event. Bangkok Tribune -- 12 national marine parks under watch for coral bleaching [strong El Nino 2023-24 (sea warming after the peak)]
• 2024-05-10 (bleaching, Gulf of Thailand incl. Koh Tao (Surat Thani)): Thailand closed 12 national marine parks on 10 May 2024 (including Mu Koh Chumphon and Hat Khanom-Mu Koh Thalay Tai, near Samui); 50% of Gulf of Thailand reefs were bleached including at Koh Tao, 20% in the Andaman; the bleaching began in April and was expected to last to July, attributed to El Nino-linked sea warming. The Nation -- Thailand shuts 12 national marine parks amid coral bleaching crisis [strong El Nino 2023-24 (sea warming after the peak)]
• 2024-05 (bleaching, Gulf of Thailand): DMCR retrospective (April 2025): the Gulf of Thailand's worst bleaching was in May 2024, affecting about 90% of corals; overall 60-80% of corals bleached, about 40% died and over 60% of the affected corals later recovered. The Nation -- Thailand's coral reefs stage impressive comeback after bleaching event [strong El Nino 2023-24 (sea warming after the peak)]
• 2024-04-04 (water_shortage, Koh Phangan / Koh Samui): Tap water on Koh Phangan was rationed on a rotating basis from late March 2024, with only 3,500-4,000 m³ a day supplied; Samui's three reservoirs held 3.2 million m³ and the island drew 22,000 m³ a day (plus 5,000 in the dry season) through the undersea pipeline from Surat Thani. El Nino is not named in this article. The Thaiger -- Water crisis hits Koh Pha-ngan and Koh Samui, tap water rationed [strong El Nino 2023-24 (its dry season)]
• 2024-04-04 (water_shortage, Koh Samui / Koh Phangan): Thai PBS World confirmed rationing on Pha-ngan since late March 2024 (reservoir capacity 740,000 m³, desalination 600 m³ a day) and said the drought on both islands was worse than in previous years. Thai PBS World -- Water shortages on Samui and Pha-ngan islands ahead of Songkran [strong El Nino 2023-24 (its dry season)]
• 2024-04 (heat, Thailand (southern east coast rain at 82% of normal)): TMD's April 2024 summary: several places set new all-time highs and the monthly mean temperature was 2.6 °C above normal; the southern east coast (Gulf side) received 65.4 mm, 82% of normal. Thai Meteorological Department -- Monthly summary, April 2024 [strong El Nino 2023-24 (its dry season)]
• 2024-04 (heat, Thailand): More than three dozen districts across Thailand's 77 provinces set April records in 2024; Lampang reached 44.2 °C, Bangkok's heat index passed 52 °C and power demand hit a record 36,699 MW on 29 April. No southern-province figure is given. The Pattaya News -- Record-breaking heatwave continues across Thailand [strong El Nino 2023-24 (its dry season)]
• 2023-07-02 (water_shortage, Koh Samui): In July 2023 Koh Samui's freshwater reserves were said to cover only about 30 days of demand; water plants produced 15,000 m³ a day and residents paid 250-300 baht for about 2,000 litres when taps ran dry; the report ties the shortage to El Nino. The Thaiger -- Water crisis grapples Koh Samui as rising tourist demands amplify freshwater shortage [strong El Nino 2023-24 (developing year)]
• 2023-07-02 (water_shortage, Koh Samui): Koh Samui was facing a shortage of freshwater in July 2023 due to a lack of rainfall and increased water demand. Bangkok Post -- Freshwater shortage hits Samui [strong El Nino 2023-24 (developing year)]
• 2022-12-18 (storm, Koh Samui / Koh Phangan / Koh Tao ferries): All ferry services between the mainland and Samui, Phangan and Tao were suspended on 18-19 December 2022 as a strong northeast-monsoon surge brought 2-4 m waves; Seatran and Raja Ferry offered refunds or rebooking. The Thaiger -- Heavy rains close Gulf ferries, Surin Islands for 2 days [La Nina 2022-23 (not an El Nino year)]
• 2019-09-23 (haze, Phuket / southern Thailand): On 23 September 2019 smoke from Indonesian plantation fires cut Phuket's visibility below 1 km with particulate readings three times the 50 µg/m³ upper limit; Narathiwat exceeded 150. The Thaiger -- Smoke-laced smog envelops Phuket [weak El Nino 2018-19 (Indonesian fire season)]
• 2019-01-05 (storm, Koh Samui): During Pabuk about 20,000 tourists were on Koh Samui; all transport to the mainland was suspended, beaches closed, one person died and one was missing from a capsized fishing boat, and over 6,100 people were evacuated in four provinces. ABC News (Australia) -- At least one dead on capsized boat as Tropical Storm Pabuk batters Thailand [weak El Nino 2018-19 (not one of the strong events)]
• 2019-01-04 (storm, Nakhon Si Thammarat / Koh Samui / Surat Thani): Tropical Storm Pabuk made landfall at Pak Phanang just after midday on 4 January 2019 (45 mph winds), the first January tropical cyclone in Thai records since 1951; 30,000 were evacuated in Nakhon Si Thammarat, Gulf ferries were suspended, Nakhon Si Thammarat and Surat Thani airports closed and red flags flew on Samui beaches. The Weather Channel -- Tropical Storm Pabuk makes first on record southern Thailand January landfall; two killed, thousands evacuated [weak El Nino 2018-19 (not one of the strong events)]
• 2017-01-09 (flood, southern Thailand (12 provinces incl. Surat Thani, Nakhon Si Thammarat)): DDPM figures on 9 January 2017: 21 dead, 2 missing, 958,602 residents affected in 12 southern provinces since 1 January; 1 billion m³ of floodwater in the Pak Phanang basin; 218 road sections, 59 bridges and 2,253 schools damaged. The Nation -- No let-up as flood toll hits 21 [weak La Nina 2016-17, the winter after the 2015-16 El Nino]
• 2017-01-05 (flood, Koh Samui / southern Thailand): AP, 5 January 2017: eight southern provinces flooded since 1 January, at least 3-5 dead, rail and six long-distance bus routes cut, and flooding on Samui snarled traffic and delayed flights. Fox News (AP) -- Flooding disrupts transit, spoils holidays in south Thailand [weak La Nina 2016-17, the winter after the 2015-16 El Nino]
• 2016-12-05 (flood, southern Thailand incl. Koh Samui): A tropical depression on 1-2 December 2016 plus the northeast monsoon dropped over 500 mm on the southern coast between 1 and 7 December 2016; the retrospective says the flooding killed 91 and affected 360,000 and shows flooded Koh Samui streets (figures differ between tallies). The Weather Network -- Remembering the Thailand floods that lasted more than a month [weak La Nina 2016-17, the winter after the 2015-16 El Nino]
• 2016-12-03 (flood, Koh Samui): A local blog (secondary) documents the 3-5 December 2016 flooding in Bang Rak, Chaweng, Choengmon and Maenam: roads closed, dive and snorkel boats stopped, some Samui flights delayed, and the island declared a disaster zone on 5 December. Camille's Samui Info blog -- Flooding on Koh Samui [weak La Nina 2016-17, the winter after the 2015-16 El Nino]
• 2016-10-10 (water_shortage, Koh Samui): October 2016: Samui's two Pru Krajude reservoirs (800,000 m³ combined) were drying up after a long rainless spell; the desalination plant at full output could not meet the island's demand of 30,000 m³ a day, rationing was in force, trucks carted water to villages and the remaining reservoir water was expected to be unusable within a week. Bangkok Post -- Severe water shortage on Koh Samui [very strong El Nino 2015-16 (the dry spell that followed it)]
• 2016-09-30 (water_shortage, Koh Samui): Water zoning was introduced on Koh Samui on 30 September 2016, with rationing of tap water to households and businesses. Bangkok Post -- Water rationing on Koh Samui as reservoirs dry up [very strong El Nino 2015-16 (the dry spell that followed it)]
• 2016-09-30 (water_shortage, Koh Samui): By late September 2016, after a long rainless spell, Koh Samui was on alternating-zone tap water supply; the Mared subdistrict reservoir was dry and large hotels were buying trucked water at more than 100,000 baht a month. ThaiResidents -- Serious water shortage on Koh Samui [very strong El Nino 2015-16 (the dry spell that followed it)]
• 2016-05-27 (bleaching, Thailand (Rayong to Satun, both coasts)): On 26-27 May 2016 Thailand's national parks department indefinitely closed at least ten dive sites after surveys found bleaching on up to 80% of some reefs; the closures were to be reviewed before the November high season. ABC News (Australia) -- Thailand closes ten popular dive sites in bid to slow down coral bleaching crisis [very strong El Nino 2015-16]
• 2016-03-30 (drought, Thailand (national; the South is not named)): On 30 March 2016 Thailand was reported to be in its worst drought in decades, with 22 of 76 provinces affected and some major dams below 10% of capacity; the report attributes it to El Nino and does not mention southern Thailand or Samui. Al Jazeera -- Thailand hit by its worst drought in decades [very strong El Nino 2015-16]
• 2016-01-25 (flood, Koh Samui / Koh Phangan): Storms hit the southern islands including Koh Samui and Koh Phangan in late January 2016, causing floods and the suspension of ferry services between Surat Thani and Koh Samui: the NE monsoon still floods the island in an El Nino winter. Bangkok Post -- Samui, Phangan swamped by floods, ferry service halted [very strong El Nino 2015-16 (its NE-monsoon winter)]
• 2016 (paper, Thailand (total and extreme precipitation)): Limsakul A., Singhruck P. (2016), Long-term trends and variability of total and extreme precipitation in Thailand, Atmospheric Research 169: 301-317. Atmospheric Research -- Long-term trends and variability of total and extreme precipitation in Thailand [context]
• 2015-10-09 (haze, Phuket / Samui / southern Thailand): Haze from Indonesian fires blanketed the southern Thai islands in October 2015: five flights bound for Phuket and Samui turned back to Bangkok on 8 October and two Singapore-Phuket flights circled for up to an hour; the fires were worsened by El Nino-driven dry conditions. ABC News (Australia) -- Smog from Indonesian forest fires blankets Thailand's southern islands, including Phuket and Samui [very strong El Nino 2015-16 (Indonesian fire season)]
• 2013 (paper, Western Gulf of Thailand (1998 and 2010 bleaching)): Sutthacheep M. et al. (2013), Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand, Deep Sea Research Part II 96: 25-31. Deep Sea Research II -- Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand [El Nino 1997-98 and 2009-10]
• 2013 (paper, Western Gulf of Thailand (1998 and 2010 bleaching)): Sutthacheep M. et al. (2013), Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand, Deep Sea Research Part II 96: 25-31. Deep Sea Research II -- Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand [El Nino 1997-98 and 2009-10]
• 2011-03-31 (flood, southern Thailand incl. Samui, Koh Tao, Koh Phangan): By 31 March 2011 at least 21 were dead and about a million people affected; the navy carrier Chakri Naruebet evacuated 734 holidaymakers from Koh Tao and Koh Phangan, and Samui flights had resumed. Al Jazeera -- Thai military searches for mudslide victims [La Nina 2010-11 (not an El Nino year)]
• 2011-03-30 (flood, Koh Samui / southern Thailand): Late-March 2011 floods and mudslides killed at least 21 people in the South (7 in Nakhon Si Thammarat, 3 in Surat Thani); 80 districts of eight provinces were declared disaster areas, over 50 flights were grounded and about 2,000 people were stranded on Samui. Al Jazeera -- Deaths as heavy rain hits Thailand [La Nina 2010-11 (not an El Nino year)]
• 2011-03-30 (flood, Koh Samui): On 29 March 2011 all 53 Bangkok Airways flights in and out of Koh Samui were cancelled, Firefly suspended flights because the airport was flooded, and 3 m waves suspended the ferries between Samui and Surat Thani. TTG Asia -- Tourists still stranded on Koh Samui [La Nina 2010-11 (not an El Nino year)]
• 2011-02-08 (bleaching, Thailand (18 dive sites)): Thailand's DNP shut 18 popular dive sites for up to 14 months after the 2010 bleaching, in the second-hottest year on record; tourism was affected. Inside Climate News -- Coral bleaching outbreak in Thailand shutting dive sites and slowing tourism [El Nino 2009-10]
• 2011-01-20 (bleaching, Thailand): January 2011: more than half of Thailand's 38,000 acres of reef were bleached and sites where bleaching reached 80% were closed indefinitely; the Andaman Sea reached 34 °C in April-May 2010. Yale Environment 360 -- Reef dive sites in Thailand closed after damage from coral bleaching [El Nino 2009-10]
• 2010-12 (bleaching, Thailand national parks (both coasts)): After a DMCR recommendation the DNP closed 18 popular dive sites in 7 of 26 marine national parks on both sides of the peninsula for 6-18 months; the Gulf of Thailand was less impacted than the Andaman coast. Reef Resilience Network -- Malaysia & Thailand: Disturbance Response (case study) [El Nino 2009-10]
• 2010-11-03 (flood, Koh Samui): Koh Samui airport suspended services amid torrential rain and flooding in early November 2010; the Surat Thani mainland and Don Sak were also flooded, with power outages and businesses shut. C9 Hotelworks -- Koh Samui airport closes amid torrential flooding [La Nina 2010-11 (not an El Nino year)]
• 2010-06 (bleaching, Gulf of Thailand and Andaman Sea): Yeemin et al. (2012): sea surface temperatures of 30-34 °C in March-June 2010, bleaching over 80% at several sites; mortality about 50-60% in the Andaman Sea and 30-40% in the Gulf of Thailand; 2010 judged similar in extent to 1998 but more severe in the Gulf. Yeemin et al. 2012 -- Impacts of coral bleaching, recovery and management in Thailand (12th International Coral Reef Symposium) [El Nino 2009-10]
• 2010-06 (bleaching, Koh Tao): In 2010 many reef areas around Koh Tao experienced 95% coral bleaching with 78% mortality on parts of some reefs such as Chalok Baan Kao; by the February 2011 survey the mushroom corals had recovered. PMBC Research Bulletin 71 -- Hoeksema, Matthews & Yeemin 2012 [El Nino 2009-10]
• 2005 (paper, Thailand (summer monsoon rainfall)): Singhrattna N., Rajagopalan B., Krishna Kumar K., Clark M. (2005), Interannual and interdecadal variability of Thailand summer monsoon season, Journal of Climate 18(11): 1697-1708. Journal of Climate -- Interannual and interdecadal variability of Thailand summer monsoon season [context]
• 2005 (paper, Southeast Asia incl. the peninsula): Juneng L., Tangang F.T. (2005), Evolution of ENSO-related rainfall anomalies in Southeast Asia region and its relationship with atmosphere-ocean variations in the Indo-Pacific sector, Climate Dynamics 25: 337-350. Climate Dynamics -- Evolution of ENSO-related rainfall anomalies in Southeast Asia region [context]
• 1998 (bleaching, Koh Tao / western Gulf of Thailand): Koh Tao's first major coral bleaching event occurred in 1998 (Hoeksema, Matthews & Yeemin 2012, Phuket Marine Biological Center Research Bulletin 71: 71-81). PMBC Research Bulletin 71 -- The 2010 coral bleaching event and its impact on the mushroom coral fauna of Koh Tao, western Gulf of Thailand [very strong El Nino 1997-98]
• 1998 (bleaching, Koh Tao): A Koh Tao reef-monitoring NGO page (secondary) states the 1998 mass bleaching was devastating to the island; for 2010 it gives 98.1% of surveyed corals bleached and island coral cover falling from 41.2% to 27.1%. New Heaven Reef Conservation -- Koh Tao Reef Status [very strong El Nino 1997-98]

Looked for, not found

• Koh Samui water shortage or rationing in the 2019-20 dry season (searched The Thaiger, Samui Times, Khaosod English, Thai PBS: only 2016, 2023, 2024 and 2026 reports surfaced)
• Koh Samui water shortage in 1998 (El Nino 1997-98) and in 1992-93
• Samui / Koh Tao-specific bleaching percentages for 2016
• DDPM casualty and affected-population tallies for Tropical Storm Pabuk (January 2019)
• a November 2011 flood on Koh Samui

Method

Events: the strong / very strong El Ninos of the NOAA CPC ONI table since 1950; their peak ONI and RONI are read from the CPC series stored by this app (series oni, roni). For each event the island's water year (July of the developing year to June of the next) is rebuilt from ERA5 daily data for the Maenam grid cell (Open-Meteo archive, models=era5, elevation 10 m, the same cell as the live rain-deficit factor): Oct-Dec (NE monsoon refill), Jan-May (dry season) and Feb-Apr rain as % of the 1991-2020 mean of the same cell; max feels-like and days at or above 39 °C feels-like / 35 °C in Jan-May; the longest run of days under 1 mm. Neutral years (ONI within +-0.5 °C from SON to FMA) give the baseline (median). Numbers are monthly aggregates computed once from the daily data (fetched in decade windows, one per run, to respect the shared Open-Meteo quota) and cached in status samui_era5_history; the current year is refreshed daily. Documented impacts come from dated reports whose URL was checked live; nothing is inferred from the numbers.

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)