For the second time this week, the highest heat index monitored in the country so far this year was recorded in Dagupan City, Pangasinan.
READ: Record heat continues: 53C heat index registered in Dagupan City
The 53 degrees Celsius (°C) heat index recorded on Friday, May 14, broke the previous highest heat index of 52°C recorded in the same city last Wednesday, May 12.
Given its topography, a weather specialist of the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) said hot weather conditions are expected in Pangasinan's capital because it is part of the Agno River Valley.
PAGASA weather specialist Benison Estareja likened Dagupan City's condition to Tuguegarao City, Cagayan and Echague, Isabela which are also experiencing hot temperatures.
"Part kasi ang Dagupan City ng Agno River Valley, so mainit din talaga yung buong valley. Same with Tuguegarao (Cagayan) and Echague, Isabela na record-high din ang air temperatures. are part of Cagayan Valley naman. (Because Dagupan City is part of the Agno River Valley, so the whole valley is really hot. Same with Tuguegarao, Cagayan and Echague, Isabela where air temperatures are also record-high. Tuguegarao and Echague are part of Cagayan Valley)," Estareja told the Manila Bulletin.
Sun exposure is also more intense in areas situated in a valley which makes the air warm faster, he said
"Areas beneath the valley form few clouds and little rain, as compared to areas in and near the mountains. Mataas ang sun exposure (Sun exposure is more intense) plus air that enters the valley warm quickly," he added.
This also probably explains why the highest recorded air temperature in the Philippines of 42.2 degrees Celsius was also recorded in Tuguegarao, Cagayan on May 11, 1969.
Air temperature is different from heat index as the latter is the measurement of how hot it feels when relative humidity is factored in with the actual air temperature.
Heat index is at least 3°C to 4°C higher than the actual air temperature.