Bangkok heat index stays in danger zone for 18 straight days

Bangkok remains under severe heat stress after the city’s Environment Department reported that the heat index on April 18, 2026 was still in the “danger” category, marking the 18th consecutive day since April 1 that the capital has remained in a health risk zone.

The heat index measures the temperature the human body actually feels by combining air temperature with relative humidity, making it a more accurate reflection of heat stress than the maximum temperature alone.

When the heat index reaches 42 to 51.9 degrees Celsius, it is classified as “danger”.

At that level, the risk of abnormal symptoms rises sharply, including fatigue, dizziness, skin rashes and muscle cramps. In more serious cases, it can lead to heatstroke, which can be life-threatening.

Authorities are urging the general public to monitor their health closely.

Vulnerable groups, including young children, older people, pregnant women, those with chronic illnesses, people with obesity, drinkers, outdoor workers, outdoor exercisers and tourists, have been told to avoid daytime outdoor activity and seek medical attention immediately if unusual symptoms develop.

The BMA classifies the heat index into four levels.

• A reading of 27.0 to 32.9 degrees Celsius is considered “watch”, with people advised to follow heat warnings and, especially in risk groups, drink water regularly.
• A reading of 33.0 to 41.9 degrees Celsius is considered “warning”, with outdoor activity recommended to be reduced between 11am and 3pm.
• A reading of 42.0 to 51.9 degrees Celsius is categorised as “danger”,
• Anything above 52 degrees Celsius is considered “extreme danger”, at which point outdoor activity should be stopped altogether.

The prolonged run of dangerous heat underscores the growing pressure on public health in Bangkok as extreme weather intensifies, with officials continuing to warn residents to take precautions against heat-related illness.