PAGASA is monitoring a low pressure area (LPA) 205 kilometers west northwest of Calayan island in Cagayan.
This weather system is intensifying the southwest monsoon.
In turn, the monsoon is bringing moderate to occasional heavy rains in the western section of Luzon, including Metro Manila.
Most of the rains are expected to pour on Thursday.
Rains will become less frequent on Friday and Saturday.
Fair weather is seen by Sunday.
The LPA off Cagayan is set to leave the Philippine Area of Responsibility (PAR) either tonight or tomorrow morning.
It might still develop into a tropical depression outside PAR.
PAGASA is also eyeing a second weather disturbance.
Severe tropical storm "Sanvu" is estimated to be 2,150 kilometers east northeast of Basco, Batanes.
Sanvu is outside PAR and is not expected to affect the weather across the country.