Tropical storm "Fabian" (international name "In-fa") and a tropical depression outside the Philippine area of responsibility are expected to further enhance the southwest monsoon or "habagat" that will induce monsoon rains over most of Luzon and Visayas in the next few days.
In its 5 p.m. bulletin issued on Sunday, July 18, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) estimated the center of Fabian at 1,095 kilometers (km) east-northeast of extreme northern Luzon.
It has slightly intensified with maximum sustained winds of 75 kilometers per hour (kph) near the center and gustiness of up to 90 kph.
PAGASA said Fabian may become a severe tropical storm by Monday afternoon, July 19, and into a typhoon by Tuesday afternoon, July 20.
Meanwhile, the tropical depression west of Luzon was estimated at 770 km west of Basco, Batanes on Sunday afternoon.
PAGASA senior weather specialist Chris Perez said the two tropical cyclones will remain far from the Philippine landmass but both weather systems may continue to enhance the habagat and induce monsoon rains in the coming days.
In the next 24 hours, Palawan may experience scattered to widespread moderate to at times heavy monsoon rains.
Metro Manila and the rest of Luzon, Central and Western Visayas, Northern Mindanao, Zamboanga Peninsula, Tawi-Tawi, Sulu, and Basilan may also experience scattered light to at times moderate to heavy rains and thunderstorms due to the southwest monsoon.
The rest of Visayas and Mindanao will have partly cloudy to cloudy conditions with rain showers or thunderstorms.
Perez said most of Luzon and Visayas, particularly the western sections, may experience monsoon rains in the next two to three days.
PAGASA warned against possible flash floods or rain-induced landslides during heavy or prolonged rainfall, particularly in areas that are highly susceptible to these hazards.
"Fabian will remain far from the Philippine landmass throughout the forecast period. The tropical cyclone is forecast to move northwestward in the next 24 hours and will exit the northern boundary of the Philippine area of responsibility on Monday evening or Tuesday morning," PAGASA said.
"Fabian will then generally move westward near the northern boundary of the PAR. Due to the uncertainty of the track, a southward shift of the track of Fabian may increase the likelihood of re-entering the PAR," it added.