The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) reported that Guiuan, Eastern Samar experienced a 51-degree Celsius (°C) heat index on Monday, May 20.

On May 18, a similar level was recorded but it decreased by 1°C on May 19.
READ: https://mb.com.ph/2024/5/19/pagasa-monitors-50-c-heat-index-in-e-samar-on-may-19
This heat index is only 1°C below the "extreme danger" category and just 2°C short of matching the all-time high of 53°C recorded in Iba, Zambales.
PAGASA reported that Roxas City, Capiz recorded a heat index of 48°C, followed by Butuan City, Agusan Del Norte, at 47°C.
The heat index reached 46°C in Bacnotan, La Union; Sangley Point, Cavite; Virac (Synop), Catanduanes; Catarman, Northern Samar; and Maasin, Southern Leyte.

A heat index of 45°C was logged in Laoag City, Ilocos Norte; Dagupan City, Pangasinan; and Masbate City, Masbate, while 44°C in Aparri, Cagayan; ISU Echague, Isabela; Iba, Zambales; Ambulong, Tanauan Batangas; Aborlan, Palawan; Cuyo, Palawan; Daet, Camarines Norte; Iloilo City, Iloilo; Dumangas, Iloilo; and Zamboanga City, Zamboanga Del Sur.
The heat index reached 43°C at the Ninoy Aquino International Airport (NAIA) Pasay City, Metro Manila; Science Garden Quezon City, Metro Manila; CLSU Muñoz, Nueva Ecija; Cubi Pt., Subic Bay Olongapo City; Coron, Palawan; Catbalogan, Samar; Dipolog, Zamboanga Del Norte; and Cotabato City, Maguindanao.
Meanwhile, it reached 42°C in Tuguegarao City, Cagayan; Casiguran, Aurora; Legazpi City, Albay; La Granja, La Carlota, Negros Occidental; Panglao International Airport, Bohol; Siquijor, Siquijor; Tacloban City, Leyte; VSU-Baybay, Leyte; Borongan, Eastern Samar; Laguindingan Airport, Misamis Oriental; Davao City, Davao Del Sur; and Surigao City, Surigao Del Norte.
On May 20, 41 areas reached the "danger" heat index.