The Philippine Atmospheric, Geophysical and Astronomical Services (PAGASA) has issued a flood advisory for Marikina River on Wednesday evening, June 9, due to threats of flooding, as well as landslides, brought about by the monsoon rains.
In the initial advisory issued at 8:30 p.m., PAGASA said watercourses that are likely to be affected by flooding are the upper and lower portions of Marikina River in Rodriguez, Antipolo, and San Mateo in Rizal, Quezon City, Marikina City, and Pasig City.
Likewise, Marikina River tributaries, Mango River (Rodriguez, Rizal), and Nangka River (Marikina City and San Mateo and Antipolo in Rizal), were also likely to be affected by flash floods.
"People living near the mountain slopes and in the low-lying areas of the abovementioned cities and local disaster risk reduction and management councils concerned are advised to be alert for possible flash floods and landslides," PAGASA warned.
"Local flooding is possible in some areas due to poor drainage system and impounding water," it added.
The advisory is valid until 8 a.m., Thursday, June 10.
In its weather bulletin issued at 5 p.m., Wednesday, PAGASA said the monsoon trough is expected to bring isolated to scattered rain showers and thunderstorms over most of the country.
PAGASA weather specialist Ariel Rojas explained that the monsoon trough is part of the intertropical convergence zone or ITCZ that is connected to the monsoon system or "habagat," which has circulations or low pressure systems.
It is a typical source of tropical cyclones in the Western North Pacific from June to September, he added.
In the next 24 hours, the monsoon trough will bring scattered rain showers and thunderstorms over Metro Manila, the rest of Luzon, Visayas, Zamboanga del Norte, Zamboanga del Sur, Zamboanga Sibugay, Basilan, and Tawi-Tawi.
Rojas advised those in these areas to remain vigilant against possible flash floods or landslides due to occasional moderate to at times heavy rains.