BANGKOK, June 25 -- Bangkok residents have been warned to stay out of the midday sun after the city's heat index - the temperature the human body actually feels - climbed to a dangerous 51.9degC, just shy of the highest warning category.

According to The Nation, Thailand's Environment Department and Meteorological Department placed the capital in the "Danger" zone today, urging people to avoid unnecessary outdoor activities between 11am and 3pm because of the heightened risk of heatstroke.

Unlike the recorded air temperature, the heat index combines heat and humidity to measure how hot conditions feel to the human body. High humidity limits the body's ability to cool itself through perspiration, increasing the risk of heat-related illne...