As temperatures continue to rise across the country, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) regularly issues heat index advisories to help Filipinos stay safe.
But what exactly is the heat index, and how are its levels classified?
What is the Heat Index?
Heat index, according to Engr. Al Quiblat, chief of the Visayas radar of the Philippine Atmospheric Geophysical and Astronomical Services Administration (Pagasa), is the temperature people feel.
It combines air temperature with relative humidity. It is also why it’s often referred to as ‘temperature apparent’.
“Kung sa Tagalog, damang init. Ug kung sa Bisaya pa, ang init nga mabati,” said Quiblat in an interview with CDN Digital.
(In Tagalog, it;s ‘damang init.’ In Bisaya, it’s ‘init nga mabati.’)
PAGASA’s Heat Index Classification
PAGASA categorizes heat index values into four levels, each indicating potential health risks:
1. Caution (27°C to 32°C)
At this level, fatigue is possible with prolonged exposure and physical activity. While conditions are generally tolerable, it’s best to stay hydrated and avoid strenuous outdoor tasks during peak hours.
2. Extreme Caution (33°C to 41°C)
This range increases the risk of heat cramps and heat exhaustion. Symptoms may include heavy sweating, weakness, dizziness, and nausea. Limiting outdoor exposure and taking frequent breaks in shaded or cool areas is advised.
3. Danger (42°C to 51°C)
At this stage, heat cramps and heat exhaustion become likely, and heat stroke becomes possible with continued exposure. The body struggles significantly to regulate temperature, making it critical to stay indoors, drink plenty of fluids, and monitor for warning signs such as confusion or fainting.
4. Extreme Danger (52°C and above)
This is the highest alert level, where heat stroke is imminent with prolonged exposure. Avoid outdoor activities entirely and seek air-conditioned environments when possible.
Why Heat Index matters
Given the country’s tropical climate, high humidity levels often push heat index values far beyond actual temperatures. During the dry season—especially from March to May—some areas experience heat index levels in the “Danger” or even “Extreme Danger” categories.
Urban areas are particularly vulnerable due to the “urban heat island” effect, where concrete surfaces absorb and retain heat, further raising perceived temperatures.
Safety tips during high heat index days
People cannot escape extreme heat but there are multiple ways to prevent heat-related illnesses, including heat stroke.
- Stay hydrated: Drink water regularly, even if you’re not thirsty
- Avoid peak hours: Limit outdoor activity between 10 a.m. and 4 p.m.
- Wear light clothing: Choose loose, breathable fabrics
- Seek shade or cool spaces: Rest in shaded or air-conditioned areas
Understanding the heat index isn’t just about comfort—it’s about safety. By knowing PAGASA’s classification system, Filipinos can better prepare for extreme heat and protect themselves during the hottest days of the year.
