MANILA - Storm surges of up to 6 meters (approximately 19 feet) are likely to hit the coasts of Cagayan, Isabela and Ilocos Sur as Ompong approaches landmass, the state weather bureau warned Thursday.

In a press briefing, PAGASA forecaster Nikos Peñaranda said storm surges may hit the areas of Aparri, Palanan, and the whole coastline of Ilocos Sur.

"Ito po based sa historical storm surge data. Sa past events, maaari pong abutan ng 5 to 6 meters," he said, adding that Ompong may start to bring storm surges by Friday.

Peñaranda asked the public to watch out for PAGASA's storm surge warning in their next updates, where they will specify the exact locations that may be hit by surges.

"Inaabisuhan po natin ang mga manlalayag na huwag muna maglayag, especially doon sa mga may signals na lugar dahil sa panganib sa karagatan," he added.

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Ompong continues to pack maximum sustained winds of 205 kph near the center and gusts of up to 255 kph, but it "slightly slowed down" at 20 kph, PAGASA said in its 11 a.m. weather bulletin.

It is expected to make landfall in northern Cagayan on Saturday morning (September 15), PAGASA said. An earlier forecast show Ompong may become a supertyphoon before making a landfall.

Tropical cyclone warning signal no. 1 have been raised over 20 areas in northern, central, and southern Luzon as the 900-km wide typhoon may also enhance the southwest monsoon.

• Ompong slows down; Signal no. 1 up in 24 areas

Forecaster Peñaranda said Northern Luzon will experience heavy to intense rains beginning Friday and will peak on Saturday when Ompong makes a landfall.

PAGASA's forecasts show Baguio and Tuguegarao will receive the highest rainfall amount on Saturday. Monsoon rains also will bring occasional heavy rains to Palawan, Zamboanga, and Visayas.