At least 11 areas across the Philippines recorded heat index values of 42 to 43 degrees Celsius on Nov. 1, reaching the danger level, based on the latest data issued by the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA).

Catarman, Northern Samar, and Dipolog, Zamboanga del Norte, recorded the highest heat index at 43 degrees Celsius, according to PAGASA’s five-day heat index computation with a two-day forecast issued as of 5 p.m. on Sunday.

Nine other areas recorded a heat index of 42 degrees Celsius including:

• Ilocos Region

• Bacnotan, La Union (Ilocos Region)

• MIMAROPA

• Coron, Palawan

• San Jose, Occidental Mindoro

• Bicol Region

• Daet, Camarines Norte

• Legazpi City, Albay

• Negros Island Region

• Siquijor, Siquijor

• Eastern Visayas Region

• Borongan, Eastern Samar

• Maasin, Southern Leyte

• Caraga Region

• Hinatuan, Surigao del Sur

The heat index measures how hot the temperature feels to the human body when relative humidity is taken into account.

PAGASA classifies heat index values of 42 to 51 degrees Celsius as dangerous. Prolonged exposure to these conditions may cause heat cramps and heat exhaustion, while continued physical activity can increase the risk of heatstroke.

The public is advised to limit outdoor activities, especially during the hottest hours of the day, stay in shaded or well-ventilated areas, drink plenty of water and wear lightweight, loose-fitting clothing.