Manila, April 13 -- The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) on Sunday warned of dangerous heat index levels in 20 areas in the country.

Heat index refers to the temperature felt by the human body when relative humidity combines with air temperature.

In its 5 a.m. forecast, PAGASA said the following areas may have heat indices ranging from 42C to 45C on Sunday:

Sangley Point, Cavite - 44C Virac, Catanduanes - 44C San Ildefonso, Bulacan - 44C Dagupan City, Pangasinan - 43C Ambulong, Tanauan, Batangas - 43C Cuyo, Palawan - 43C Masbate City, Masbate - 43C Roxas City, Capiz - 43C Iloilo City, Iloilo - 43C Tuguegarao City, Cagayan - 42C Cubi Pt., Subic Bay, Olongapo City - 42C Bacnotan, La U...