The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) has officially declared the onset of the southwest monsoon, locally known as the Habagat season, in the country.
In an advisory released Friday, May 30, 2025, the weather bureau said that the declaration follows the consistent presence of low-level southwesterly winds and a frontal system affecting several regions in the country. Additionally, the weakening of easterly winds contributed to the shift in weather patterns that mark the beginning of the Habagat.
According to PAGASA weather specialist Benison Estareja, the return of the southwesterly wind flow over parts of the country has signaled the early phase of the monsoon season. With this development, residents, particularly in the western section of the country, should brace for frequent rains and thunderstorms in the coming days.
PAGASA also noted that while the rainy season has not been formally declared, its onset is expected within the next two weeks.
The bureau issued a heavy rainfall outlook spanning from today until Monday, June 2, warning of significant rainfall volumes that could lead to flooding and landslides, especially in mountainous and elevated areas.
From May 30 to May 31, up to 200 mm of rainfall is expected in Ilocos Norte, Ilocos Sur, Zambales, and Batanes. Moderate rainfall ranging from 50-100 mm is forecast in Cagayan, Isabela, La Union, Pangasinan, Bataan, Apayao, Abra, and the Babuyan Islands.
From May 31 to June 1, Ilocos Norte, Ilocos Sur, La Union, Pangasinan, Zambales, Bataan, Batanes, and the Babuyan Islands will continue to experience moderate rains. The same pattern is likely to persist until June 2.
PAGASA emphasized that previous rainfall may worsen the effects of the upcoming downpours. Residents and local government units are urged to take preventive measures and stay alert for local Heavy Rainfall Warnings and Thunderstorm Advisories issued by PAGASA’s regional offices.
The bureau clarified the distinction between a Heavy Rainfall Warning and a Weather Advisory. The former provides precise short-term forecasts (within three hours) and is Doppler radar-based, while the latter offers broader 24-hour provincial-level outlooks.