Thirteen areas across the country are expected to experience heat indices under the "danger" category on Sunday, according to the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

Dagupan City, Pangasinan; Tuguegarao City, Cagayan; and ISU Echague, Isabela may expect a 44°C heat index.

Based on its latest data, PAGASA said the following areas may have dangerous heat indices ranging from 42°C to 43°C:

* Bacnotan, La Union - 43°C

* Aparri, Cagayan - 43°C

* Maasin, Southern Leyte - 43°C

* NAIA, Pasay City - 42°C

* Baler, Aurora - 42°C

* Casiguran, Aurora - 42°C

* Infanta, Quezon - 42°C

* Malunay, Quezon - 42°C

* Iloilo City, Iloilo - 42°C

* Catbalogan, Samar - 42°C

According to PAGASA, 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.

The weather bureau said that danger level heat index may cause heat cramps, exhaustion, and heat stroke with continued exposure to the sun.

To prevent heat-related illnesses, PAGASA encouraged the public to limit their time spent outdoors, drink plenty of water, avoid tea, coffee, soda, and liquor, wear umbrellas, hats, and sleeved clothing outdoors, and schedule heavy-duty activities for the beginning or end of the day when it is cooler.

PAGASA announced on Friday the end of the El Niño phenomenon.

El Niño, according to PAGASA, is characterized by unusually warmer than average sea surface temperatures in the central and eastern equatorial Pacific.

El Niño increases the likelihood of below-normal rainfall conditions, which could bring negative impacts (such as dry spells and droughts) in some areas of the country.