When you wake up, do you feel sweaty? Or after a bath, do you feel hot?
You might have checked the temperature on television or your phone and saw it was 36 degrees Celsius (°C)—that's just the "actual air temperature."
The "heat index," on the other hand, will show that it is hotter than you think.
The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) weather specialist Veronica Torres explained that the air temperature is the temperature of the surroundings being measured.
The relative humidity, meanwhile, is the moisture content in the atmosphere.
These two, when combined, result in the heat index record.
Simply put, heat index refers to the temperature felt or perceived by the human body.
“Tinitingnan natin iyong relationship ng actual air temperature at ng relative humidity at iyon ang macocompute na heat index (We look at the relationship of the actual air temperature and the relative humidity, and that is what we would have computed as heat index),” Torres said.
For example, in May 2023, PAGASA reported an actual air temperature of 35°C in Aparri, Cagayan, combined with a relative humidity of 67 percent, resulting in a heat index felt at 49°C.
Torres added that there is a possibility of an increase in air temperature during the dry and warm season because the Earth's tilt, which prolongs the daytime hours, increases heat.
Classifications, effects of heat index
PAGASA said "caution" is required in areas where the heat index is between 27 and 32°C.
Extended exposure and activity can cause fatigue, while continuous activity can result in heat cramps.
Meanwhile, "extreme caution" should be exercised in areas where the heat index is between 33 and 41°C because prolonged activity may result in heat stroke, heat exhaustion, and cramps, PAGASA said.
It added that a "dangerous" heat index of 42–51°C increases the risk of heat stroke and that the body is likely to experience heat exhaustion and cramps.
Moreover, it said that for those living in areas with a heat index of 52°C or higher, heat stroke is imminent.
What can be done?
PAGASA said that individuals with heat-related illnesses may sweat heavily, feel exhausted, dizzy, and weak, and experience vomiting or nausea.
To avoid the negative effects of the heat index during the warm and dry season, PAGASA advised the public to limit going outside, to stay hydrated with plenty of water, to refrain from drinking tea, coffee, soda, and liquor, to always bring umbrellas, hats, and clothes with sleeves, and do heavy-duty tasks at the end of the day when it already is cooler.