Heat indices in 11 areas reached the “danger” level on Saturday, according to the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

In its two-day heat index forecast based on computed data from 25 to 29 March, PAGASA said the heat index or the so-called "init factor" might reach 43°C and 42°C on 30 and 31 March, respectively, in the Ninoy Aquino International Airport area in Pasay City.

Other parts of the country expected to record dangerous levels of heat index are: Iba, Zambales at 42°C, Alabat, Quezon at 44°C, Calapan, Oriental Mindoro at 42°C, San Jose, Occidental Mindoro at 43°C, Puerto Princesa City, Palawan at 44°C, Roxas City, Capiz at 44°C, Mambusao, Capiz at 42°C, Iloilo City at 43°C, Dumangas, Iloilo at 43°C, and La Granja, La Carlota, Negros Occidental at 43°C.

PAGASA considers a heat index reaching 42°C to 51°C as "dangerous."

According to the state weather bureau, heat index refers to the so-called “init factor” and to the apparent heat felt by a person when high air temperatures are combined with humidity.

PAGASA warned of heat-related illnesses such as heat cramps or heat exhaustion during extreme heat.

It advised the public to reduce outdoor activities, stay hydrated, and avoid certain beverages to prevent heat-related ailments.

The agency also advised the public to use umbrellas, hats, and wear sleeved clothing when outdoors, and to schedule strenuous activities for cooler times of the day.

PAGASA formally declared the beginning of the dry season on 23 March.