Residents are being urged to stay at home with the powerful storm expected to make landfall on Wednesday.

Governor Lou Leon Guerrero on Tuesday urged residents in the United States territory to remain calm and prepare for the cyclone.

“Mawar is a real threat and a possible direct hit to our island,” the governor said in a YouTube video on Tuesday.

The weather service said Mawar could hit the southern part of Guam at about midday local time (02:00 GMT) on Wednesday.

“If we don’t take a direct hit, it’s going to be very close,” Patrick Doll, lead meteorologist for the National Weather Service in Guam, told The Associated Press news agency.

The storm is expected to arrive as a 140 mph (225 kph) Category 4 typhoon, weather officials said, possibly delivering the biggest hit to the island in 20 years.

The typhoon could cause “extensive damage,” Doll warned.

The governor said she would place Guam in an effective lockdown from 1pm (03:00 GMT) on Tuesday and urged people to take the warnings seriously and be prepared. Emergency shelters were available, she said.

A storm surge of between 6 and 10 feet (1.82 to 3 metres) above the normal high tide was expected with warnings that it could be as much as 15 feet (4.6 metres). Surf was expected to build sharply in the next day or two along south- and east-facing reefs, with dangerous surf of 20 to 25 feet (6 to 7.6 meters) Tuesday afternoon into Wednesday, the weather service said.

At the island’s grocery and hardware stores on Monday, people were leaving with shopping carts full of canned goods, cases of water and generators, the Pacific Daily News reported.

Officials warned residents not living in fully concrete structures to consider moving for their own safety. Many homes are made of wood and tin.

“The triple threat of cat 4 typhoon force winds, torrential rains and life-threatening storm surge are all expected for Guam and Rota,” the weather service said in a Tuesday morning update.

Rota, an island in the US Commonwealth of the Northern Mariana Islands, was also subject to a typhoon warning, Doll said. Tinian and Saipan, in the northern Marianas, were under tropical storm warnings.

Some people in those areas are still in temporary shelters or tents after Category 5 Super Typhoon Yutu in 2018, Doll noted.

“Guam takes a Category 4 or 5 hit every five to seven years. Mother Nature has spared us as of late,” Doll said, adding that the last direct hit was in 2002. “So we are way overdue.”