(Updates with position of storm, changes byline)
By David Alire Garcia
MAZATLAN, Mexico, Oct 22 (Reuters) - Hurricane Willa, an extremely dangerous a Category 4 storm, weakened slightly as it veered toward popular tourist resorts on Mexico's Pacific coast on Monday, prompting government warnings for people to leave high-risk areas and take cover.
Mexican authorities urged residents to evacuate their homes for temporary shelters, closed ports, canceled classes and suspended beachside and marine activities.
The storm was due to come ashore after lunch on Tuesday just south of Mazatlan, a popular beach resort in the northwestern state of Sinaloa. Several other tourist destinations in the neighboring state of Nayarit also lie near to the storm's path.
Willa, which earlier in the day had been a Category 5 on the five-step Saffir-Simpson scale, was blowing maximum sustained winds of near 150 miles per hour (240 kph) by evening with higher gusts, the U.S. National Hurricane Center (NHC) said.
Complete power outages, damage to roofs and even the foundations of buildings that are up to 500 meters (1,640 feet) from the coastline were possible, Mexico's National Meteorological Service (SMN) said.
In Sinaloa, Tuesday classes were cancelled in towns stretching more than 120 miles (200 km) across the state, including Mazatlan, as well as in all of Nayarit.
Alberto Hernandez, head of the SMN, said the storm would probably be a Category 4 or 3 hurricane when it reached land, and could cause waves several meters (feet) high.
It could also lead to the formation of waterspouts in front of the coast of Puerto Vallarta, the SMN said, referring to another beach resort in the state of Jalisco next to Nayarit.
Nearly three years ago to the day, Hurricane Patricia, one of the most powerful storms on record, struck Mexico close to Puerto Vallarta with winds that tore down trees, moved cars and forced thousands of people to flee homes.
Speaking in the western city of Guadalajara, President Enrique Pena Nieto warned the population to prepare for the arrival of Willa and urged residents to take cover.
The storm was about 100 miles (160 km) west of the town of Cabo Corrientes and is "expected to be a dangerous major hurricane when it reaches the coast of Mexico", the NHC said.
Willa is moving northward and is forecast to gradually lose power during the next day or so and weaken rapidly after hitting the coast, the Miami-based hurricane center added.
The SMN urged residents to "exercise extreme caution" as rains have softened the soil in some areas. Willa's downpours could cause landslides, flooding and damage to roadways.
The NHC said that the Air Force Reserve Hurricane Hunter Aircraft that was en route to Willa experienced a safety issue before entering the storm and had to return to base.
Willa is expected to douse coastal states Jalisco, Nayarit and Sinaloa with 6 to 12 inches (15 to 30 cm) of rain, likely triggering flash floods and landslides, the NHC said. Some areas may see as much as 18 inches (45 cm) of rainfall.
To the south, Tropical Storm Vicente weakened further, with maximum sustained winds of 40 mph (65 kph). It was churning some 310 miles (500 km) southeast of the Pacific port Manzanillo, and would likely dissipate soon, the NHC said. (Additional Julia Love and Lizbeth Diaz; Writing by Anthony Esposito and Dave Graham; Editing by Bill Trott and Sandra Maler)
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