Manila: The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) on Sunday warned of dangerous heat index levels in 20 areas in the country.According to Philippines News Agency, the 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 identified several areas that may experience heat indices ranging from 42°C to 45°C. These include Sangley Point, Cavite and Virac, Catanduanes both at 44°C, and San Ildefonso, Bulacan at the same level. Dagupan City, Pangasinan and Ambulong, Tanauan, Batangas are expected to have heat indices of 43°C, along with several other locations such as Cuyo, Palawan and Masbate City, Masbate.Furthermore, areas like Tuguegarao City, Cagayan and Cubi Pt., Subic Bay, Olongapo City are expected to experience a heat index of 42°C. Other affected areas include Bacnotan, La Union, ISU Echague, Isabela, and Puerto Princesa, Palawan, among others, all marked to have si milar heat levels.PAGASA categorizes areas with a 42°C to 51°C heat index under the danger category, advising that heat cramps and heat exhaustion are possible in areas under extreme caution. There is also a potential risk of heat stroke under the danger level. The weather bureau advised the public to avoid spending time outdoors, particularly at noon, and recommended staying hydrated. For those going outside, the use of umbrellas or wearing hats and sleeved clothing is advised.Meanwhile, in its 4 a.m. weather forecast, PAGASA mentioned that the easterlies will bring isolated rains and thunderstorms across the country. It was also noted that no tropical storm or low-pressure area is currently being monitored within the Philippine Area of Responsibility.