Best Time to Visit Thailand, Coast by Coast and Month by Month

A HelloRoam Thailand eSIM keeps you online from Bangkok to the islands. Book a Grab, check ferry times, and watch the forecast for each coast from your phone.

Here's the short version by region:

• Bangkok and central Thailand: November to February. April is the hottest month and September the wettest.
• Chiang Mai and the north: November to February, with nights near 60°F in January. February to April can be hazy, and March and April are hot.
• Phuket, Krabi and the Andaman coast: December to March. September and October bring the most rain.
• Koh Samui and the Gulf islands: February to September. November is the wettest month.
• Both coasts on one trip: February, the driest month at both Phuket and Koh Samui.

Thailand Weather by Month in Bangkok, Chiang Mai, Phuket and Koh Samui

Thailand's National Statistical Office, using Meteorological Department data, splits the year into three seasons: hot from mid-February to mid-May, rainy from mid-May to mid-October, and cool from mid-October to mid-February. Cool is relative. Bangkok's average high still sits at 90 to 92°F from November to January.

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The table shows each month's average daily high and average rainfall at four weather stations, from the department's 1991 to 2020 climate averages, converted to °F and inches.

Read across a row and the two coasts split. In February, Phuket averages 0.9 inches of rain and Koh Samui 2.5. In November, Phuket gets 7.0 inches while Koh Samui gets 17.5, its wettest month of the year.

The Andaman and Gulf Coasts Have Opposite Rainy Seasons

From May to October, Phuket on the Andaman Sea averages 9 to 14 inches of rain a month, with the peak in September. Koh Samui in the Gulf of Thailand gets 4.0 to 5.3 inches a month from May to September. Then its rain builds through October to a peak in November.

The split holds along each coast. In the department's data, every coastal station on the Gulf side from Chumphon to Songkhla gets its most rain in November, and every Andaman station from Ranong to Satun peaks between August and October. February is the driest month at all of them.

The Andaman season opens in October. In 2026, Maya Bay on Koh Phi Phi Le reopened on October 1, and the Similan Islands reopened on October 15 after a five-month monsoon closure, the Tourism Authority of Thailand reports. TAT expects the dry season proper by December. It also warns that October and early November can still bring rain and that boat operators sometimes hold back when waves run high, so build a spare day into island plans.

Six marine national parks, including Similan, Surin, Phi Phi, Phang Nga Bay and Koh Lanta, have used electronic tickets since October 2025. TAT's advice: buy yours in advance and have your passport ready.

Book early for December and January. TAT advises reserving ferries and island stays ahead for those months, and suggests about ten to twelve days to see several Andaman provinces without rushing. If Phuket is your base, here's where to stay in Phuket and how to get around.

Koh Samui runs on the opposite clock. February and April are its driest months, at 2.5 and 3.3 inches, and December is its third-wettest month, at 10.4 inches. A December beach trip works better on the Andaman side.

March is the only other month inside both coasts' best windows, with 3.2 inches of rain in Phuket and 4.6 on Koh Samui.

Bangkok Is Hottest in April and Wettest in September

Bangkok's average high peaks at 96°F in April. From May to October the city averages 15 to 21 rainy days a month, with the most rain in September (13.2 inches) and October (11.4 inches). December is the driest month, at half an inch.

Songkran, the Thai New Year water festival, comes back each April. The 2026 festival ran from April 13 to 15, according to TAT, right in the hottest weeks. In Bangkok, Silom and Siam Square turn into major water-fight zones, and TAT advises planning travel in advance.

Chiang Mai and the North Are Best From November to February

Nights get cool in the north. Chiang Mai averages a low of 60°F in January and 62°F in December, with highs of 85 to 91°F and under 2 inches of rain a month from November to February. That's the comfortable window for trekking and temple days.

Haze builds through the cool season. On average, Chiang Mai's weather station logs haze on about 8 days in November, 22 in February and 27 in March. April is the hottest month, with an average high of 98°F. In March 2019, air quality in parts of the north sat at unhealthy levels for weeks, and TAT told visitors to Chiang Mai and Chiang Rai to watch air quality reports. It blamed the haze mostly on forest fires, open burning and vehicle emissions. Before a trip between February and April, check the Pollution Control Department's Air4Thai readings for Chiang Mai, and check again once you're there.

For the US travel advisory and other risks, see our Thailand safety guide for Americans.

Loi Krathong falls on the full moon of the 12th Thai lunar month, which was November 15 in 2024. Chiang Mai celebrates it as Yi Peng, with a traditional Lanna lantern competition and the krathong sai ceremony, when lanterns float downstream. Check TAT for this year's date before you book.

The Worst Months Depend on Where You Go

October is the only month when Phuket and Koh Samui both average more than 10 inches of rain, at 13.2 and 11.6. It's also Krabi's wettest month, at 11.5 inches.

In July and August, the Gulf side is the better beach bet: Koh Samui averages 4.6 and 4.0 inches of rain, against 9.5 and 12.2 inches at Phuket.

Mobile Data and Phone Setup for a Thailand Trip

Depending on the plan, HelloRoam's Thailand eSIM connects to AIS, DTAC or TrueMove H, and support is open 24/7 by email and WhatsApp. Install it before you fly with our eSIM setup steps, so it's ready when you land.

Bought your iPhone in the US? Apple says every iPhone from the iPhone 14 on sold in the United States has no SIM tray, so a Thai SIM card won't fit.

Apple lists eSIM support on the iPhone XS, XS Max, XR and later. A travel eSIM also needs an iPhone that isn't locked to your US carrier. To check, open Settings, tap General, then About, and look for "No SIM Restrictions" next to Carrier Lock. For Android and other models, check if your phone supports eSIM.

If you'll spend most of the trip at one hotel, its Wi-Fi may be all you need. A data plan earns its keep on the move: on ferries, in a Grab, or checking the forecast for the next island.

Heading on to Malaysia or Singapore? A travel eSIM for Southeast Asia from HelloRoam covers Thailand, Malaysia and Singapore on one plan.