Thailand weather by month: all 12 months, 12 cities, from 10 years of real data

In one paragraph: November–February is the dry, cool stretch for most of the country (except the lower Gulf, where rain peaks in Nov–Dec). March–May is the hottest part of the year. May–October is the rainy season — but each coast's rainy season has a different weight: the upper Gulf (Hua Hin, Pattaya) runs systematically lighter than the Andaman side and the North.

Two things this table shows that generic guides usually don't: "rainy season" is not a reason to cancel a trip, only to pick the right city — and the Dec–Jan "high season" is not dry everywhere. Krabi still averages 154 mm in December, and Songkhla sits at 375 mm.

7 of 12 cities are under 50 mm — Khon Kaen is driest at 8 mm, Bangkok 23 mm, Chiang Mai 20 mm. Northern mornings are the year's coolest (mean minimum 14.6°C in Chiang Rai, 16.6°C in Chiang Mai). The Andaman coast is in high season but not at its driest yet: Phuket 78 mm, Krabi 84 mm. The lower Gulf is just coming out of its heavy stretch (Surat Thani 125 mm, Songkhla 149 mm).

9 of 12 cities under 50 mm — the most of any month — and Phuket's driest month of the year at 34 mm. The Surat Thani side of the Samui route drops to 40 mm. Northern mornings are still cool (Chiang Rai 15.5°C). If you want the single hardest month to get wrong before you've even picked a city, this dataset says February.

Temperatures climb (mean maximum 35.9°C in Kanchanaburi, 34.1°C in Chiang Mai) and the North hits its driest — Chiang Mai just 9 mm, Chiang Rai 15 mm. Both coasts are still workable: Phuket 62 mm, Hua Hin 49 mm. One thing that is NOT from our dataset but is common knowledge about the North: February–April is typically the smoke-haze season, so anyone sensitive to air quality should check real readings before going.

The hottest month in almost every city — mean maximum 36.7°C in Kanchanaburi, 35.5°C in Khon Kaen, 35.4°C in Chiang Mai, 34.3°C in Bangkok. Songkran in mid-April lands right on the heat peak. Rain starts returning to the lower Andaman and the east (Krabi 154 mm, Trat 156 mm), but most cities are still in the middle band.

6 of 12 cities cross into the heavy-rain band at once — Trat 301 mm, Krabi 250 mm, Phuket 230 mm, Chiang Mai 206 mm. The lighter side: Pattaya 166 mm, Hua Hin 146 mm. If May is your only window, the upper Gulf is the answer the numbers support.

Across these three months the rain champion is Trat (Koh Chang's gateway): 401 → 588 → 478 mm — July's 588 mm is the highest value of any city in any month of this table. The North peaks too: Chiang Mai climbs from 240 to 412 mm in August, Chiang Rai runs 253–354 mm.

The clearly lighter side is the upper Gulf and the Gulf's deep south: Hua Hin 106–146 mm, Songkhla 131–142 mm, Pattaya 99–176 mm — which is why a mid-year beach trip should pick the Gulf, not the Andaman (Phuket 178–207 mm, Krabi 192–218 mm).

The one month every region is wet at once — Bangkok hits its own peak at 297 mm, Khon Kaen 295 mm, Trat 529 mm, Chiang Mai 336 mm. Even the lightest city, Hua Hin, still gets 165 mm. If you can avoid one month for an outdoor-heavy trip, this dataset says September; if you can't, the lowest numbers this month are Hua Hin and Songkhla (165 and 169 mm).

The monsoon is withdrawing: Chiang Mai is down to 178 mm, Khon Kaen 169 mm. But the southern coasts are peaking — Surat Thani 316 mm, Krabi 296 mm, Phuket 290 mm, Songkhla 285 mm. By late October the North is entering its end-of-rains transition; if a mountain trip is the goal, November's lower numbers are worth the wait.

The upper half (North, Northeast, central, east) dries out clearly: Khon Kaen 40 mm, Chiang Mai 68 mm, Pattaya 72 mm, Bangkok 82 mm, with cool northern mornings arriving (Chiang Rai 18.8°C) — northern travel season has begun. The lower Gulf is another world entirely: Songkhla spikes to 495 mm, the highest of any city this month, Surat Thani (the Samui–Phangan gateway) 300 mm, Krabi 274 mm, Phuket 246 mm. No month sends "go north" and "go south" further in opposite directions.

8 of 12 cities under 50 mm — Khon Kaen 6 mm, Kanchanaburi 15 mm, Pattaya 17 mm, Bangkok 19 mm. The North is cool and dry (Chiang Mai 25 mm, mean minimum 17.5°C). Phuket drops to 140 mm, just below the heavy-rain line. The one exception is the lower Gulf: Songkhla still 375 mm, Surat Thani 196 mm, Krabi 154 mm — a New Year trip to Samui or the lower Gulf carries meaningfully more rain risk than Phuket.

Use the table to choose the month and the city, then use the real forecast to choose the day

• 10-year averages — any single year can differ a lot from the mean
• Values are at the town coordinate, not on an island or a mountain — Samui uses the Surat Thani mainland point, Koh Chang uses Trat; the islands themselves can differ
• mm/month measures total volume, not timing — tropical rain often comes as an afternoon storm and stops, not an all-day drizzle
• It does not cover sea conditions, the northern haze season, or air quality — always check official sources before travelling