The Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) warned of moderate to heavy rain showers over Metro Manila and nearby provinces within the next two hours.
In a thunderstorm advisory, Pagasa said Bulacan, Rizal, Laguna, Cavite, Batangas and Nueva Ecija may also be affected.
Thunderstorms were already observed in Cabangan and San Felipe, Zambales, as well as in Tagkawayan, Quezon, and may persist while spreading to nearby areas.
In its earlier forecast, Pagasa said Tropical Depression Paolo, now inside the Philippine Area of Responsibility, is not yet affecting the country. The rain showers and thunderstorms are caused by the easterlies, or winds blowing from the east, which will soon signal the transition from the southwest monsoon (habagat) to the northeast monsoon (amihan).
But by Friday, Paolo is forecast to bring heavy rains and make its landfall over Isabela and Aurora. It is likely to develop into a severe tropical storm, according to the weather bureau.