The Philippine Atmospheric, Geophysical, and Astronomical Services Administration (Pagasa) officially declared the start of the southwest monsoon after a two-month summer phase on Friday.

In a statement, Pagasa said recent weather analysis these past several days showed "persistence of low-level southwesterly winds over the western section of Luzon and the frontal system over extreme Northern Luzon" and the continuous weakening of easterlies.

"Occasional to frequent rains and thunderstorms are expected, particularly over the western sections of the country," Pagasa said.

Pagasa said the rainy season may begin in two weeks, and periods of monsoon breaks may also occur.

Based on Pagasa's 4pm report on Friday, Batanes may experience cloudy skies with scattered rains and thunderstorms due to frontal system.

Due to southwesterly wind flow, Metro Manila, Ilocos Region, Cordillera Administrative Region (CAR), Central Luzon, the rest of Cagayan Valley, Cavite, Laguna, Batangas, Rizal, and Occidental Mindoro will also experience cloudy skies with scattered rains and thunderstorms, Pagasa said.

The rest of the country will have partly cloudy to cloudy skies with isolated rain showers or thunderstorms due to localized thunderstorms. Kate Christian Ravelo/DMS