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A growing typhoon in the Pacific is heading toward the Mariana Islands and could lash Guam with strong winds, rain and surf this weekend.

The U.S. National Weather Service in Guam reports Typhoon Wutip was packing 100 mph (161 kph) winds and will continue to intensify through Saturday. The storm was about 480 miles (772 kilometers) southeast of Guam Friday.

Typhoon warnings remain in place for parts of the Federated States of Micronesia, and tropical storm warnings are in effect for Guam and other nearby islands. The typhoon is expected to track just south of Guam Saturday into Sunday.

"When it's near Guam, (wind) will be up to 115 mph (185 kph), but we won't see that on the island," said meteorologist Michael Ziobro of the National Weather Service in Guam.

Wutip has typhoon-force winds extending about 35 miles (56 kilometers) from its center and tropical storm-force winds up to 150 miles (241 kilometers) away.

Antoninette Arriola, a 48-year-old school aide, was doing laundry as part of her storm preparations. "After the storm is over, a lot of people are going to be here washing, so we wanted to do it before then."

She said she started her typhoon preparations earlier in the day. "We took off the tarp from outside our house that covers where we park, and we also bought some canned goods like Vienna sausage, Spam, corned beef, batteries, crackers, bread. We recently bought a small freezer so that we can put our ice and frozen meats in there."

Tyrone Quinata, 23, purchased coffee as his first storm preparation. He added batteries for his flashlights and radio. "I think we'll be fine," he said.

Chris Barcinas, 29, a heavy equipment operator, was filling his pickup truck with gasoline. He said he wasn't worried about the typhoon.

"I'm prepared. Guam's strong. We know what typhoons are," Barcinas said. "If it does come, I hope everyone stays safe and they have a good time during the typhoon," Barcinas added.

The peak season for typhoons in the region is late summer into fall, but strong storms in the winter are not uncommon.

"The Western Pacific is the only basin on the planet that has tropical cyclones year-round," said meteorologist Tom Birchard of the National Weather Service in Honolulu. "It's somewhat unusual, but it's not outside the realm of expectation."

Something that was unusual about Wutip, Birchard said, was where it formed.

"It formed at a very low latitude," Birchard said. "When you go to school and they teach you tropical meteorology, they tell you have to be more than 5 degrees from the equator for a tropical cyclone to form. Well this one formed at about 3.5 degrees north."

A westerly wind burst near the equator spun up Wutip shortly after the same winds formed tropical cyclone Oma in the southern hemisphere, Birchard said.

Westerly wind bursts in the area are often associated with El Nino weather patterns and can help create twin storms — one on either side of the equator, he said.

Last week, the National Oceanic and Atmospheric Administration announced that El Nino conditions had formed in January along the equatorial Pacific and were expected to continue into the spring in the northern hemisphere.

Sea surface temperatures near the equator where the storms formed are slightly above average, but ocean temperatures around and ahead of Wutip, where the storm will gain strength over the next two days, are not warmer than normal, Birchard said.

"With climate change, there could be areas where ocean temperatures are warmer than normal, and that could lead to increased storm formation," Birchard said. But "I've seen research on either side of that argument," noting that some studies argue that there could be fewer tropical cyclones in warmer climates because of increased vertical sheer, which can disrupt the rotation of tropical cyclones.

"If I'm looking for the primary formation mechanism in this case, it would be less of the sea surface temperature anomaly and more of the westerly wind bursts along the equator," he said.

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Associated Press correspondent Caleb Jones reported from Honolulu.