Thailand is hot all year and dangerously hot on some days between March and May, when Bangkok's heat index can pass 52 °C. Plan outdoor sightseeing for the morning and late afternoon, drink before you are thirsty, use high-factor sunscreen, and learn the difference between heat exhaustion, which you can treat yourself, and heatstroke, which is an emergency.
Most visitors cope well with the heat once they adjust their day to it. The people who get into trouble tend to be those who keep the schedule they would follow at home: a full day of temples from 10:00 to 16:00, a long walk at noon, or a hike or run in the middle of the day. Add a hangover or a stomach bug, and dehydration comes quickly.
This page covers how Thai authorities measure and warn about heat, how to plan a day around it, and the warning signs that official health services list. It is general guidance, not medical advice; if you have a heart condition, diabetes or take regular medication, ask your doctor before you travel.
Heat in Thailand: the key facts
- Hottest period
- Roughly mid-March to early May; in 2024 the heat index was highest from April to early May (MNRE)
- Thailand's record
- 44.6 °C (Mae Hong Son, 2016; Tak, 2023)
- Bangkok heat index
- Above 52 °C, "extreme danger", on 4 May 2026 (BMA)
- Warning levels
- Caution, Warning, Danger, Extreme danger (see table below)
- If someone collapses
- Call 1669
How Thailand measures heat: the four warning levels
Thai authorities warn about heat using the heat index, the temperature the body actually feels once humidity is taken into account. On a humid day in Bangkok it can be far higher than the air temperature on your weather app. The scale below is published by Thailand's environment ministry (MNRE), and Bangkok's city government, the BMA, attaches advice to each level.
| Level | Heat index | BMA advice |
|---|---|---|
| Caution (green) | 27.0–32.9 °C | Follow weather warnings; vulnerable groups drink water regularly |
| Warning (yellow) | 33.0–41.9 °C | Reduce outdoor activities between 11:00 and 15:00 |
| Danger (orange) | 42.0–51.9 °C | Monitor your condition closely; vulnerable people see a doctor if symptoms appear |
| Extreme danger (red) | 52.0 °C and above | Avoid all outdoor activities |
The BMA's list of people who should take extra care includes children under 5, people over 60, pregnant women, people with underlying conditions or obesity, people who drink alcohol, people who work or exercise outdoors, and tourists. Visitors are on the list because they are not used to the climate and tend to stay outside for long periods.
When the heat is worst
Thailand's hot season comes before the rains. In 2024, the Thai Meteorological Department declared it started on 21 February, forecast continuous extreme heat from mid-March to early May, and expected it to end around mid-May in most of the country, including Bangkok, according to the MNRE. The dates move a little each year, so check the forecast rather than a fixed calendar.
The 2024 forecast quoted by the MNRE gives a sense of the spread: maximums of 40–42 °C in the north and central regions, 38–41 °C in Bangkok, and 35–40 °C on the southern coasts. In the north, the hot months overlap with the burning season and poor air quality; our article on smoky season in Chiang Mai explains that. For how the weather changes across the year and the regions, see Thailand weather month by month and our older guide to the best time to visit.
Planning a day around the heat
The simplest rule comes from the BMA's own advice: keep hard outdoor activity out of the 11:00 to 15:00 window. That suits Thailand well. Temples and markets open early, and many sights are at their best in the soft light of late afternoon.
- Start early. Big open-air sights such as the Grand Palace are far more pleasant at opening time than at noon.
- Plan an indoor middle of the day. A museum, a shopping mall, a cooking class, a long lunch or a rest at the hotel.
- Dress for both sun and temples. Loose, light-coloured, long sleeves and trousers protect you from the sun and meet the temple dress code at the same time.
- Know where to cool off. Bangkok lists public "Heat Escape Rooms" on its Greener Bangkok website during heat warnings.
Check the daily heat index, not just the temperature. A forecast of 35 °C with high humidity can put Bangkok in the Danger band. The BMA publishes a daily forecast of the maximum heat index during the hot season, and Thai news sites report it.
Drinking enough: water, electrolytes and alcohol
The NHS advice for hot weather is to drink more cold drinks, especially when you are active, and to avoid drinking too much alcohol. In Thailand that means carrying water and drinking it before you feel thirsty. Do not drink from the tap; our page on tap water in Thailand explains what it is fine for and what it is not.
If you sweat a lot, plain water may not be enough. The NHS suggests isotonic sports drinks or oral rehydration powder mixed with water to replace the salt lost in sweat. Both are sold in pharmacies and at the convenience stores on almost every corner; see what 7-Eleven stocks. A bout of travelers' diarrhea makes dehydration much more likely, so treat the two together.
Beer by the pool counts as fluid but not as hydration. Alcohol makes heat illness more likely, which is why the BMA names drinkers as a group at risk. Our article on drinking alcohol in Thailand covers the other risks.
Heat exhaustion and heatstroke: the warning signs
The NHS describes heat exhaustion as something that usually does not need emergency help if the person can cool down within 30 minutes. Signs include tiredness, dizziness, headache, nausea or vomiting, heavy sweating with pale, clammy skin, cramps in the arms, legs or stomach, a high temperature and strong thirst.
To treat it, the NHS lists four steps: move the person somewhere cool, remove unnecessary clothing, give plenty of water or a rehydration drink, and cool the skin with water and a fan. Cold packs wrapped in cloth under the armpits or on the neck also help. They should feel better within about half an hour.
Hot, dry skin and confusion mean heatstroke: call 1669. The NHS treats heatstroke as an emergency. Signs include still feeling unwell after 30 minutes of cooling, a very high temperature, hot skin that is not sweating, a fast heartbeat, fast breathing, confusion, a seizure or loss of consciousness. While waiting, keep cooling the person with a wet sheet, a fan or cold water.
In Thailand, 1669 is the emergency medical number. Our pages on emergency numbers and hospitals in Thailand explain what happens next. A fever with headache and body aches is not always the heat; in Thailand it can also be dengue fever, so see a doctor if it does not settle.
Sunburn: why it happens faster in Thailand
Thailand is close to the equator, and the sun is strong even on cloudy days. The NHS lists people who are only occasionally exposed to intense sun, such as on holiday in a hot country, among those who need extra care. Its advice applies directly:
- Use sunscreen of at least SPF 30 with at least 4-star UVA protection, and use enough: around 6 to 8 teaspoons to cover an adult's body.
- Reapply every two hours and straight after swimming or towel drying, even if the label says water resistant.
- Stay in the shade between 11:00 and 15:00, and wear a wide-brimmed hat and sunglasses.
- Water and sand reflect UV, and the cooling effect of the sea hides the burn until later.
For mild sunburn, the NHS suggests cooling the skin with water, using an aftersun such as aloe vera and staying out of the sun until the redness has gone. Get medical help if you feel unwell or the skin blisters or swells badly. Sunscreen is sold everywhere in Thailand, but bring your preferred brand if you have sensitive skin; our packing guide has the rest of the list.
Frequently asked questions
What is the hottest month in Thailand?
Usually April. In 2024, Thai authorities expected continuous extreme heat from mid-March to early May, with the heat index highest from April to early May. The hot season usually ends around mid-May when the rains arrive.
Is it safe to visit Thailand in April?
Yes, for most healthy travelers, as long as they plan around the heat: sightseeing early and late, shade and rest at midday, plenty of fluids and less alcohol. People with heart conditions, older travelers and families with small children should take extra care and check the daily heat index.
What are the signs of heatstroke?
The NHS lists a very high temperature, hot skin that is not sweating, a fast heartbeat, fast breathing, confusion, seizures and loss of consciousness, or still feeling unwell after 30 minutes of cooling. Heatstroke is an emergency; in Thailand, call 1669 and keep cooling the person while you wait.
Sources
- Ministry of Natural Resources and Environment (MNRE) – Be prepared and adapt to the risk of heat hazards (checked October 2026)
- The Nation – Bangkok faces extreme heat alert as heat index exceeds 52°C (BMA, May 2026) (checked October 2026)
- NHS – Heat exhaustion and heatstroke (checked October 2026)
- NHS – Sunscreen and sun safety (checked October 2026)