The state weather bureau is monitoring two low pressure areas which may enhance the southwest monsoon or habagat.
In its weather outlook for June 5 to 11, PAGASA said the weak habagat will prevail over the western part of Southern Luzon until Friday, and may be enhanced by the two LPAs outside of the Philippine area of responsibility.
The first LPA, which is located east of Visayas, may develop into a tropical cyclone by the middle of the week but is not expected to make landfall, PAGASA said.
The second LPA is in the West Philippine Sea and will head towards Southern China mid-week.
The state weather bureau on Friday officially declared the start of the rainy season.
Meanwhile, the Philippine Institute of Volcanology and Seismology is still closely monitoring the activity in Taal Volcano in Batangas,
A low level activity was detected in the volcano last Friday, where weak and shallow but continuous tremors were detected.
There was also an increase in the average emission of sulfur dioxide.
Dr. Teresito Bacolcol, Phivolcs director, said there were reports of volcanic smog yesterday morning due to the increased emission of SO2.
He advised residents living near the volcano to stay at home, or to wear protective masks when going out.
Alert Level 1, which cites abnormal conditions, is still raised over Taal Volcano.