MANILA, Philippines—Parents would do well to equip their children with raincoats and umbrellas on the first day of classes as the weather bureau has said there is a high potential for rain on Monday.

Nathaniel Cruz, deputy administrator of the Philippine Atmospheric, Geophysical Astronomical Services Administration (PAGASA), said a monsoon trough over Luzon was likely to bring rains for the next few days over Luzon and the Visayas.

This “is expected to prevail in the next 3 to 5 days,” PAGASA said in a weather outlook sent out Friday.

A monsoon trough, Cruz explained, is a meeting of winds from the northeast and southwest that causes cloudy weather and rain. This weather system is similar to the intertropical convergence zone (ITCZ), where it is the eastern winds that meet.

“The monsoon trough will enhance the southwesterly flow bringing rainshowers and thunderstorms over Northern and Central Luzon today (Friday) and tomorrow (Saturday), then it will shift southwards and affect Southern Luzon, including Metro Manila and the Visayas by Sunday and Monday and cause inclement weather in these areas,” the weather bureau said.

Rene Paciente, the PAGASA weather forecaster, said the monsoon trough is enhancing the southwest monsoon over Mindanao, bringing rains to that region.

The sudden onset of rain this week is another twist in the weather pattern as Metro Manila and other parts of the country had been experiencing hot weather in the past week.

PAGASA said it has spotted a low-pressure area—a weather condition that brings rains and clouds and is the starting point of storms—560 kilometers east of Mindanao.