A low pressure area (LPA) was spotted off Davao Oriental, Pagasa said on Saturday.
If the LPA intensifies a cyclone, it will be locally codenamed Jolina.
In its 5 p.m bulletin, the weather agency said Bicol region, Visayas and Mindanao will be cloudy with moderate to heavy rain and thunderstorms.
Metro Manila, Calabarzon and Mimaropa regions will also be cloudy with light to moderate rains and thunderstorms.
Metro Manila will have cloudy skies and showers until July 31, Pagasa said. The rest of Luzon will be partly cloudy to cloudy with isolated rains or thunderstorms.
Occasionally strong winds from the southwest will prevail over Palawan and Mindanao and the coastal waters along these areas will be moderate to occasionally rough.
NEIL A. ALCOBER