A frontal system is pulling the southwest monsoon, which could bring stir rains over the western portion of Luzon on Tuesday, ABS-CBN resident meteorologist Ariel Rojas said.

State weather bureau PAGASA defines a frontal system as a boundary separating two air masses of differing temperature and quality.

The southwest monsoon or habagat on Tuesday may bring heavy to at times intense rains that may trigger flash floods or landslides in Ilocos Region, Batanes, and the Babuyan Islands, according to PAGASA.

The Cordilleras, Bataan, Zambales, Tarlac, Pampanga, and Bulacan will have cloudy skies with scattered rainshowers and thunderstorms due to the habagat.

Metro Manila and the rest of the country will likely have partly cloudy to cloudy skies with isolated rains or thunderstorms, added the weather agency.

Meanwhile, a low pressure area was spotted over the West Philippine Sea and could merge with the frontal system, Rojas said on TeleRadyo.

"May LPA din na posibleng mabuo sa silangan ng Mindanao, papasok ng PAR bukas pero malulusaw lang rin sa Huwebes," Rojas added.

(An LPA may also form east of Mindanao and enter PAR on Wednesday, but it may dissolve by Thursday.)

• Chedeng now out of PAR; habagat to continue bringing rains

For more updates, visit the ABS-CBN weather center.