By Ellalyn De Vera-Ruiz The sweltering heat across the country persists as the heat index readings reached dangerous to extremely dangerous levels in five Luzon-based Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) monitoring stations on Saturday afternoon (April 25). The PAGASA stations with the highest heat indexes recorded at around 2 p.m. on Saturday were located in San Jose, Occidental Mindoro (55 degrees Celsius); Dagupan City, Pangasinan (50 degrees Celsius); Ambulong, Tanauan City, Batangas (47 degrees Celsius); Calapan City, Oriental Mindoro (47 degrees Celsius), and Sangley Point, Cavite City (46 degrees Celsius). Heat index is the measurement of how hot it really feels when relative humidity is factored in with the actual air temperature. It is higher by at least 2 to 3 degrees Celsius from the actual air temperature. The high humidity causes sweat to evaporate slowly, which triggers the body to heat up, PAGASA earlier explained. It said warm and humid weather conditions will persist on Sunday as the easterly winds remain the dominant weather system across the country. PAGASA said to observe "caution" if the heat index is between 27 and 32 degrees Celsius because fatigue is possible with prolonged exposure and activity, while continuing activity could result in heat cramps. Meanwhile, consider "extreme caution" if the heat factor is between 32 and 41 degrees Celsius because heat cramps and heat exhaustion are possible. Continuing an activity could result in heat stroke. Expect "danger" if the heat factor is between 41 and 54 degrees Celsius as heat cramps and heat exhaustion are likely, while heat stroke is probable with continued activity. There is "extreme danger" if the heat index is over 54 degrees Celsius because heat stroke is imminent.