MANILA - (UPDATE 3) Typhoon Juan (International codename: Megi) gathered more strength and momentum as it roared toward the east coast of Northern Luzon Saturday, raising the possibility that public storm signal No. 4, the highest alert, may be declared in the affected areas, the weather bureau said.

Robert Sawi, chief weather forecaster of the Philippine Atmospheric, Geophysical and Astronomical Services Administration, said the typhoon entered the Philippine's area of responsibility at about 1 a.m. Saturday and was moving west northwest.

Weathermen said it was the strongest of the 10 weather disturbances to enter the country this year.

As of 5 p.m. Saturday, Juan was located 820 kilometers east of Northern Luzon, Pagasa said.

The typhoon's wind strength near the center had increased by 20 kilometers per hour to 140 kph since Pagasa's Friday bulletin.

Gustiness also intensified to 170 kph from 150 kph.

Juan also accelerated to 24 kph from 20 kph.

Having gathered speed, Juan was now expected to make landfall on Monday morning in the eastern coast of Cagayan instead of Monday afternoon, said Mario Palafox, Pagasa's senior forecaster.

Palafox said the storm's eye would track the provinces of Cagayan and Kalinga.

It is expected to exit Ilocos Norte on Monday afternoon, he said.

The weather agency said it would raise public storm warnings on Sunday.

Nathaniel Servando, Pagasa deputy administrator, described Juan as a "strong" typhoon, comparable to Reming, which devastated the Bicol region in 2006.

Science Secretary Mario Montejo said the storm could reach super-typhoon status as its peak winds were likely to hit 200 kph.

"Yesterday [Friday] it was 105 kph, now [Saturday] 140 kph. Tomorrow [Sunday], if it is consistent, it might reach 175. By Monday, we might look at 200 plus kph. This is alarming. The typhoon is really strong," Montejo said.

If it reaches 185 kph, a likely scenario since the typhoon has been consistently gaining speed and intensity over the past few days, Servando said they would raise public storm signal No. 4 in the provinces on the path of Juan.

"There is a big possibility that it will reach 185 kph. If it reaches that, we will raise signal No. 4," Servando said.

Storm signal No. 4 is Pagasa's highest warning.

"When it is signal No. 4, we advise total suspension of outdoor activities," Servando said.

The last time Pagasa declared signal no. 4 was in 2006 for typhoon Reming.

If the typhoon moves lower from its present course, Metro Manila might be affected, Servando said.

But present models showed that the typhoon would move higher, likely sparing the metropolis from its brunt.

"If it goes down to Central Luzon, one of the scenarios is it will indirectly affect Metro Manila, but it will be outside of the typhoon," Servando said.

Palafox said Metro Manila would experience mostly cloudy skies and scattered rains starting Sunday.

Visayas and Mindanao will also experience cloudy skies and scattered rainshowers, Pagasa said, adding this kind of weather was expected to last until Wednesday.

Pagasa officials had compared the typhoon's capacity for destruction to Basyang and Ondoy, which devastated Luzon and Manila recently.

The deadliest typhoon to hit the country in recent years, Ondoy dumped 455 millimeters of rain in the Pagasa monitoring site in Quezon City in 24 hours on Sept. 26, 2009.

Ondoy packed maximum center winds of 105 kph when it swept across Metro Manila and Luzon in September 2009, causing the worst floods in the metropolis in four decades and killing 464 people.

Basyang, with sustained winds of 120 kph, pounded Luzon in July this year, killing more than 100 people.

But based on satellite images on Saturday, Juan's rainfall is estimated at 200-250 millimeters in six hours, about half of Ondoy's rains, Servando said.

Pagasa, he said, would be able to make a more accurate rainfall forecast as the cyclone comes closer.

Pagasa officials said they have been directed by President Benigno Aquino III to make hourly updates on the typhoon, the 10th weather disturbance to hit the country.

Pagasa warned local governments to prepare for flashfloods, landslides, and strong winds.

Because of the typhoons strength, Pagasa also advised fishermen and vessels to stay in sheltered ports.

"Rough seas [are expected in] the coastal areas of Cagayan, Isabela, Aurora, and Quezon becoming rough and dangerous to all types of sea vessels by tomorrow [Sunday]," the agency said.

Office of Civil Defense chief Benito Ramos said they have been coordinating with local executives in Cagayan and Isabela to prepare for the oncoming storm.

Disaster response teams in these provinces as well as the Philippine Navy and the Coast Guard have been put on standby, Ramos said.

The OCD and Pagasa were also monitoring the status of the major rivers and dams in Northern Luzon.

Doctor Susan Espinueva, chief of Pagasa's hydro-metrology, said the agency was closely monitoring the water level at Magat Dam in Cagayan.

As of 4 p.m. Saturday, Espinueva said the dam had a deficit of 3.73 meters.

It will need 120 mm of rainfall to reach its normal water level, she said.

The other three major dams in Luzon - Angat, Pantabangan, and San Roque - also suffered from double-digit deficits in water level. -The Inquirer Network/ANN