* Waves of 3 meters possible off 6 provinces

* Rosita weakening since battering Northern Marianas

* Typhoon is 18th to hit Philippines this year

MANILA - The Philippines raised storm warning levels on Monday and began evacuating some coastal communities in the path of a typhoon that threatened storm surges, landslides and floods triggered by heavy winds and rain.

Typhoon Rosita (international codename Yutu), which caused havoc last week with a direct hit on the U.S. Northern Mariana islands, was set to make landfall on Tuesday morning and move across the main island of Luzon before leaving the Philippines 24 hours later, the state weather agency PAGASA said.

By mid-morning on Monday, Rosita was about 400 km (249 miles)east of the mainland and had weakened to sustained wind speeds of 150 km per hour (93 mph), with gusts of 185 kph, from 170 kph recorded a few hours earlier.

That was less intense than four days ago, when as a super typhoon with wind speeds of over 270 kph barreled through the Marianas, a U.S. Western Pacific archipelago of 52,000 people, tearing off roofs, overturning vehicles and cutting off power and water.

Authorities in Isabela and Cagayan provinces started moving residents in coastal towns to evacuation centers while the mountainous Cordillera region was put on red alert for landslides.

• Evacuations start as Luzon braces for Rosita

Three provinces in north Luzon were elevated to warning signal 3 on the severity scale of 5, and 28 more put on the earliest warnings of 1 and 2, with strong winds and rains expected later on Monday.

Known locally as Rosita, the typhoon will be the 18th to hit the Philippines this year and comes six weeks after super typhoon Mangkhut tore across Luzon, triggering landslides that killed dozens of people and damaged about $180 million of crops.

School classes were suspended in at least five provinces and fishermen in Luzon and the eastern seaboard advised not to go to sea, with warnings of storm surges of up to three meters in six provinces.

All boat services in the port city of Batangas, about 83 km (52 miles) south of Manila, were suspended on Monday.

About half of the Philippines' 105 million population live in the Luzon region. The country is hit by an average 20 typhoons each year.