Thirty-two areas in the Philippines are expected to have a dangerous heat index on Monday, with the municipality of Aparri in Cagayan forecasting its hottest temperature kicking at 46°C.

The latest report from the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) shows that 45°C is likely to hit Dagupan City in Pangasinan, Tuguegarao City in Cagayan Ambulong in Tanauan, Batangas, Coron and Aborlan in Palawan, San Jose in Occidental Mindoro, Virac (Synop) in Catanduanes, and Roxas City in Capiz.

Meanwhile, 44°C is predicted at Laoag City and Mariano Marcos State University at Ilocos Norte, Bacnotan in La Union, Isabela State University in Echague, Isabela, Sangley Point in Cavite, Puerto Princesa City in Palawan, Iloilo City and Dumangas in Iloilo, and Guiuan in Eastern Samar.

Temperature peaking at 43°C is on the other hand seen at Sinait in Ilocos Sur, Central Bicol State University of Agriculture in Pili, Camarines Sur, Mabusao in Capiz, La Granja in La Carlota Negros Occidental, and Dipolog in Zamboanga del Norte; and 42°C in Ninoy Aquino International Airport in Pasay City, Science Garden in Quezon City, Nueva Vizcaya State University in Bayombong, Nueva Vizcaya, Tayabas in Quezon, Legazpi City in Albay, Maasin in Southern Leyte, Zamboanga City in Zamboanga del Sur, Davao City in Davao del Sur, and Butuan City in Agusan del Norte.

29°C; the lowest heat index, prevails in Baguio City and Benguet State University in La Trinidad.

The weather state bureau defines heat index, also called the init factor, as the human discomfort index that gives the "apparent" temperature, or what humans perceive or feel as the temperature affecting their body.

The effect-based danger classification ranges from 42°C to 51°C, and its effects on the body are that heat cramps and exhaustion are likely, and heat stroke is probable with continued exposure.

The public is encouraged to take preventive measures against heat-related illnesses, including limiting time spent outdoors, drinking plenty of water, and wearing protective and comfortable clothing outdoors.