Living Through Koh Samui's Rainy Season: A Renter's Guide (2026)

Koh Samui's rainy season catches some renters off guard, mainly because the island sits on the Gulf of Thailand side and runs on the opposite monsoon pattern from Phuket and the Andaman coast. If you're moving here or renewing a lease, it's worth understanding what the rainy season actually looks like in measured data, what has actually gone wrong in recent years, and what to check on a property before you sign, rather than relying on general "Thailand rainy season" advice that assumes the wrong coast.

When is the rainy season, and how much does it actually rain

Because Koh Samui faces the Gulf of Thailand, its wettest period is driven by the northeast monsoon and falls later than the rainy season on Thailand's Andaman coast: October through December, with November the clear peak month. Thailand's Meteorological Department (TMD) climate normals, based on 1991–2020 data, put average monthly rainfall at approximately 295 mm in October, 445 mm in November, and 263 mm in December — meaning November alone typically brings close to half a metre of rain on average.

These are long-term averages, not a forecast for any specific year — actual rainfall in a given November can run well above or below this figure, as the events below show.

What has actually happened in recent years

In December 2024, heavy rain over consecutive days saturated a hillside in the Maret subdistrict of Koh Samui, triggering a landslide that buried a construction workers' camp; two Myanmar nationals were reported missing and subsequently confirmed dead. The wider Surat Thani province also saw serious flooding that December, with tens of thousands of people affected on the mainland and further flooding and waves battering the region into January 2025 — though the mainland flood reporting we could verify names districts like Kanchanadit, Tha Chang and Chaiya, and neighbouring Koh Phangan, rather than confirming a separate, specifically-named disaster-zone declaration for Koh Samui itself beyond the landslide event. The landslide and flooding on Koh Samui are the most clearly documented severe weather events on the island in recent years.

A separate, larger flooding disaster hit southern Thailand in late November 2025, with provinces such as Songkhla and Nakhon Si Thammarat severely affected. Reporting on how directly Koh Samui itself was hit that time is mixed — some accounts suggest the island came through comparatively lightly compared with the hardest-hit provinces, though we could not find a single authoritative source confirming the island's exact rainfall or damage for that specific event. One extreme rainfall figure (around 774 mm in a month) appears in different sources attached to different months (December 2024 in one source, November 2025 in another) without a way for us to independently confirm which is correct — treat any single extreme monthly figure you see quoted online with some caution and check the TMD's own station data if you need a precise number.

Ferries, flights and power

Ferries between Koh Samui and the mainland or neighbouring islands can and do get suspended during storms or heavy seas — this is a real, recurring risk during the October–December window, not a rare event, though we found no source with a reliable annual count of how often it happens in a typical rainy season. Build slack into travel plans around this period rather than booking tight connections.

For flights and power outages specifically, we could not find reliable, current statistics on how often either is disrupted on Koh Samui during the rainy season. The island's electricity provider (PEA) has ongoing grid-strengthening work, and general storm-safety advisories exist, but neither amounts to a frequency figure. Treat both as things that "can happen" during heavy weather rather than as a scheduled or quantified risk — and keep a basic contingency (a torch, a power bank, a flexible flight date if possible) rather than assuming either is unlikely enough to ignore.

Flooding: what our local team sees on the ground

There is no official, street-level flood risk map for Koh Samui. Based on our team's own experience living on the island, flooding shows up somewhat more often on the east-coast side than elsewhere, but in genuinely heavy rain, standing water can appear almost anywhere on the island, including spots that don't normally flood. Most of these events are short-lived and not severe rather than a routine hazard — but "which area floods" is really a question about a specific plot's drainage, not a neighbourhood-wide reputation. Our guide to where to live on Koh Samui goes into more detail on this by area.

A counterintuitive twist: water shortages during the wet season

It sounds contradictory, but heavy rain and water shortage can happen on Koh Samui in the same year. According to our local team, 2026 has been a year with a genuine water shortage in shifting parts of the island, and the Provincial Waterworks Authority (PWA) has been running a rotating zone shut-off plan since 3 August 2026 to manage supply. This has nothing to do with whether it's currently raining — it's about mains capacity and distribution, not rainfall — so don't assume that renting during or after a wet month protects you from a dry tap. If water security matters to you, ask a prospective landlord directly whether the property has had rotating shut-offs in 2026, and whether it has a backup: a water delivery arrangement by tanker truck, or its own well/borehole. Check which zones are currently affected before you sign, since the situation shifts by area over time.

Preventing mould during the wet months

Standard mould-prevention advice from health authorities such as the US EPA and CDC applies just as well on Koh Samui as anywhere humid: ventilate rooms regularly even when it's raining, run air conditioning or a dehumidifier in closed rooms, dry out any wet surface or fabric quickly rather than letting it sit, and check for damp patches on walls and ceilings periodically through the wet season. None of this is Samui-specific, but it is genuinely useful during a stretch where a villa can stay closed up and humid for days at a time.

What to check on a rental before the rainy season

If possible, view a property once during or right after heavy rain, not only on a dry day — it's the single best way to see how a specific plot actually handles the wet season, rather than relying on its neighbourhood's general reputation. Our guide to finding a long-term rental on Koh Samui covers the rest of the vetting process.

Rainy-season checklist

• Build a few days of slack around any ferry-dependent travel plans in October–December.
• Keep a basic power-outage kit (torch, power bank) on hand during the wettest months.
• Run a dehumidifier or air conditioning periodically in closed rooms, even when you're away.
• Ask your landlord directly how the property handled the last rainy season before signing.
• Separately, ask whether the property has been affected by 2026's rotating water shut-offs, and what backup water source it has.
• View the property during or right after rain if you can, not only on a dry day.
• Check your lease's terms on water damage responsibility in advance.

Frequently asked questions

When is the rainy season on Koh Samui, and how much does it rain?

October through December, driven by the northeast monsoon, with November as the wettest month — Thailand Meteorological Department climate normals (1991–2020) put average November rainfall at around 445 mm. This is later than the rainy season on Thailand's Andaman coast (Phuket, Krabi), because Koh Samui faces the Gulf of Thailand side. Actual rainfall in any single year can run well above or below this long-term average.

Has Koh Samui had serious flooding recently?

Yes — in December 2024, saturated ground from heavy rain triggered a landslide on Koh Samui that killed two construction workers, alongside flooding. The wider Surat Thani mainland and neighbouring Koh Phangan saw serious flooding the same month. A separate, larger flooding disaster hit southern Thailand in November 2025, though how directly Koh Samui itself was affected that time is less clearly documented.

Do ferries stop running during the rainy season?

Ferries can be suspended during storms or heavy seas, and this happens periodically during the October–December window. There's no reliable published figure for how often, so build slack into travel plans during this period rather than booking tight connections.

How do I stop mould in a rental during the rainy season?

Ventilate rooms regularly, run air conditioning or a dehumidifier in closed spaces, dry wet surfaces quickly, and check walls and ceilings periodically for damp patches. This general advice from health authorities like the EPA and CDC applies well to Koh Samui's humid, closed-up villas during the wet months.

Does it rain more where the water shortages are on Koh Samui in 2026?

No — the two are unrelated. According to our local team, 2026 has seen rotating water shut-offs managed by the Provincial Waterworks Authority (PWA) since 3 August 2026, driven by mains supply and distribution capacity, not by rainfall. Ask a landlord directly whether a property has been affected and what backup water source it has.

Sources

Last checked: 19 September 2026. Facts were cross-checked against several sources; official ones take priority.

• Local knowledge of the properties-away team (2026-09-19)
• TMD Climate Normals 1991–2020 (Thailand Meteorological Department) (2025-08-05)
• Landslide on Koh Samui leaves two missing amid heavy rain (The Thaiger) (2024-12-15)
• Two Myanmar Workers Dead in Koh Samui Construction Site Landslide (Khaosod English) (2024-12-15)
• Huge waves, floods batter Surat Thani, including Koh Phangan (Bangkok Post) (2025-01)
• Real-Time Coverage of the Flood Situation in the South (Thai Government PR) (2025-11-25)
• PEA เดินหน้าปรับปรุงระบบไฟฟ้าเกาะสมุย เสริมความมั่นคง (PEA grid works) (2026-08-30)
• A Brief Guide to Mold, Moisture and Your Home (US EPA) (2026-02-18)
• Mold — CDC (2024-09-26)
• ดูแลบ้านช่วงฤดูฝนอย่างไร ปลอดภัยจากเชื้อรา (Department of Health Thailand) (2025-09-16)