Bangkok has entered the highest alert zone short of the government’s most severe heat warning after the city’s heat index climbed to 51.9°C, prompting authorities to urge residents to limit outdoor activities during the hottest hours of the day.

The Environment Department and the Thai Meteorological Department reported that the capital’s heat index reached the “Danger” category, reflecting not the actual air temperature but the temperature the human body perceives under existing weather conditions.

Officials advised people to reduce outdoor exposure between 11am and 3pm, when heat-related health risks are considered most acute. They also warned that prolonged exposure could increase the likelihood of heatstroke and other heat-related illnesses.

According to the departments, the heat index is calculated by combining air temperature and relative humidity. High humidity limits the body’s ability to cool itself through perspiration, causing temperatures to feel significantly hotter and increasing physical stress on the body.

An updated weather report issued on Thursday, June 25, 2026, placed Bangkok in the red zone, indicating conditions within the “Danger” range.

Thai authorities classify heat conditions into four levels. A heat index between 27.0°C and 32.9°C falls under the “Watch” category, while readings from 33.0°C to 41.9°C are considered a “Warning” level. The “Danger” category covers heat index values from 42.0°C to 51.9°C. Any reading of 52°C or higher is classified as “Very Dangerous.”

At the current level, authorities are encouraging residents to monitor their physical condition closely and seek medical attention if unusual symptoms develop.

Health officials noted that excessive heat can affect people both directly and indirectly. Early signs of heat-related illness may include fatigue, dizziness, skin rashes, redness and swelling of the skin, and muscle cramps. If symptoms worsen and remain untreated, they can progress to heatstroke, a potentially fatal condition.

The government has identified eight groups requiring particular attention during periods of extreme heat. These include young children aged five and under, people aged 60 and above, pregnant women, individuals with underlying medical conditions, people classified as obese, those who consume alcoholic beverages, outdoor workers such as motorcycle taxi drivers, delivery riders and construction workers, as well as tourists and people exercising outdoors.

As part of its response, authorities have opened “Bangkok heat escape rooms” across the city to provide relief from extreme conditions. Locations are available through official city channels.

Residents can also monitor real-time heat conditions through the AIR BKK application and the associated LINE account. In cases of emergency illness or suspected heatstroke, authorities advise calling the 1669 emergency hotline immediately.

With Bangkok now at the upper limit of the government’s “Danger” category, public health agencies are continuing to monitor conditions closely while urging vulnerable residents and those spending time outdoors to remain alert to the effects of extreme heat.