The Heat Is On! Know Your Heat Index

Following PAGASA’s recent announcement of the onset of the hot, dry season, one of the common terms that we usually come across during weather reports, especially in this season is the heat index. What exactly is heat index, and what makes it such a “hot” term these days?What is heat index?Heat index or “apparent temperature” refers to the approximation of “how hot it feels” for a given combination of air temperature and relative humidity. Typically, heat index entails varying levels of discomfort depending on the level of heat that the body feels. As per the Humidex Index of Apparent Temperature illustrated by EuroWeather in order to graphically represent the combinations of temperatures and relative humidity possible, the varying levels of discomfort are as follows:

  • Up to 29°C – there is typically no discomfort felt
  • From 30°C to 34°C – a slight sensation of discomfort is felt
  • From 35°C to 39°C – strong discomfort is felt. It is suggested to limit heavy physical activities at this point
  • From 40°C to 45°C – strong indisposition sensation is felt. As it is starting to be a dangerous level; avoiding any kind of effort is suggested.
  • From 46°C to 53°C – this entails serious danger, so one should stop all physical activities.
  • Over 54°C – hazardous levels that may result in imminent heatstroke.

You can avert disaster by understanding the signs behind heat exhaustion that may lead to a severe medical emergency such as heat stroke. ( ) If you are staying in highly-urbanized areas, arm yourself with information about weather and its potential effects on your body. Remember that the urban heat island effect (UHI) occurs during both daytime and nighttime. UHI means that urbanized areas warm up faster than surrounding rural areas. Generally caused by land alterations and more physical and human activities, people in urban areas are advised to take more precautionary measures that will protect them from the effects of excessive heat. The urban landscape changes rapidly with continued human activity and development works in ever-expanding city centers. More and more urban regions reduce soil moisture and vegetation coverage. This results to further change in the redistribution of solar radiation based on varying heat levels in specific areas, thus increasing surface temperature.During the hot, dry season, our bodies perspire to maintain its temperature within proper physiological limits. Our sweat, mostly made of H2O or water, evaporates and this takes away the heat, providing a cooling effect on the skin. This is why we need to constantly hydrate more during warmer periods of times. To be best prepared for these situations and avoid any threat to our health, everyone is advised to always check out the latest temperature and heat index readings in their specific locations.Fortunately for us, there are tons of ways to learn about the weather, including websites that distribute free weather information such as However, if you are always on the go and want weather information at your fingertips, there is also a tool that could help. Weather Solutions, a partner of WeatherPhilippines Foundation, launched last year a free mobile app, WeatherPH, which provides seven-day localized weather forecasts for various locations within the country. WeatherPH app is available for both Android and iOS ( the WeatherPH app today and weather-check the areas you are visiting this hot, dry season. It pays to stay ahead of the weather by being #WeatherWiser!Interested about being #WeatherWiser? Contact us–By Josa Marie Salazar
Sustainability Specialist, WeatherPhilippines Foundation, Inc.
References: studies by (Howard 1833; Landsberg 1970; Oke 1982; Arnfield 2003; Yow 2007; Jin and Shepherd 2005, 2008; Zhou and Shepherd 2009)

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