Weather bureau PAGASA debunked Monday text messages that said potential supertyphoon Mangkhut will be packing 240 kph winds by Thursday this week, and gusts of up to 306 kph by the weekend.

"It's a hoax. We don't know yet how strong the typhoon will be," weather forecaster Ezra Bulquerin told ABS-CBN News.

He added that Mangkhut, which will be named "Ompong" once inside the Philippine area of responsibility, could still strengthen while in the water but will need to have maximum sustained winds of over 220 kph to be classified a supertyphoon.

"We are expecting on Thursday cloudy skies and scattered rainshowers and thunderstorms over the whole Luzon. The western sections of Visayas and Mindanao will also have the effect of the enhanced southwest monsoon, which could bring to moderate to occasionally heavy rains," he said in a separate interview with ANC's Dateline Philippines.

In a separate monitoring by ABS-CBN News, Mangkhut will come in packing sustained winds of 215 kph but can develop into a supertyphoon within the next 12 to 24 hours.

PAGASA categorizes a weather system with maximum sustained winds of 220 kph as a supertyphoon, but Ompong can carry winds of up to 250 kph before it leaves the Philippines as it approaches extreme northern Luzon, said ABS-CBN resident weather specialist Nilo Millanes.

Typhoon "Maymay" (international name: "Jebi") also packed winds of 250 kph, he said.

Its winds will weaken to 240 kph as it leaves PAR on late Saturday, he said.

Meanwhile, the Japan Meteorological Agency estimated Mangkhut's current strength at 150 kph, same with Joint Typhoon Warning Center’s. However, the JMA does not expect the weather disturbance to become a super typhoon.

The strongest winds Mangkhut will attain as per JMA’s forecast is 205 kph on Thursday until it is over Extreme Northern Luzon.