Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) has declared the onset of rainy season. “Rainy season” refers mainly to the wet season particularly in Metro Manila and mostly the western part of Luzon and Visayas.

Rain in this region is mainly characterized by afternoon showers / thunderstorms fueled by the warm moist air coming from the West Philippine Sea. Expect rainfall (i.e. late afternoon showers/thunderstorm), possible threats of flooding, landslide, and the peak of typhoon season.

The Philippines has four regions of distinct climate types based on monthly averaged rainfall of certain regions.  Type I climate, mainly in the western part of Luzon and Visayas and includes Metro Manila, has 2 pronounced seasons: dry from November to April (Northwest monsoon; Amihan) and wet during May to October (Southwest monsoon; Habagat).

Warm moist air from West Philippine Sea (South China Sea) fuels thunderstorms during the wet season of climate type I region, while on Northeast monsoon months, moist air from the Pacific ocean falls on climate type 4 region (east coast of Luzon) and is depleted/dried out by the time it reaches the western coast of Luzon.  Hence, what is meant by “rainy season” is rainy season of Climate Type I region.

There are three synoptic weather stations in Metro Manila operated by PAGASA with WMO standards (Science Garden in Quezon City, Port Area in Manila and in NAIA). An objective criteria for declaring “rainy season” is when these three stations observed rainfall for five (5) consecutive days.

Philippine Climate Map

This month, heaviest rainfall in Metro Manila was observed in Science Garden station on Wednesday (June 17)  and Thursday (June 18) last week with 50.6 mm and 38 mm, respectively, falling under a 3 hour period.

HOW TO MAKE SENSE OF PAGASA’S RAINFALL ADVISORIES

PEAK OF TYPHOON SEASON

Based on data from PAGASA, the months with the most number of tropical cyclones (TCs) are July, August and September; whereas the most number of TCs make landfall in the months October, November and July.

In terms of intensity, the months of July to October have the most TC activity with the stronger TCs occurring beginning from July onwards. On average, Typhoon (TY) is the most frequent category for TCs entering the Philippines for most months of the year, except for January to March.

MAKING SENSE OF PAGASA’S NEW PUBLIC STORM WARNING SIGNAL

The Weather Advisory is provided by the Oscar M. Lopez Center for Climate Change Adaptation and Disaster Risk Management Foundation, Inc. (OML Center) in collaboration with Dr. Gerry Bagtasa, an Atmospheric Physicists from UP Diliman and team member of DOST Project NOAH. The Center is a not-for-profit research organization funded by the Lopez Group of Companies. We seek to provide science-based information for sound decision-making. To know more about the OML Center, visit our website at http://www.omlopezcenter.org/ (Story/Photo by: Dr. Gerry Bagtasa and Jane Delfino)