Other atmospheric conditions have also contributed to formation of Category 5 cyclone.
Fiji has declared a state of emergency as the South Pacific island nation experiences the strongest storm ever recorded there.
Cyclone Winston is the equivalent of a Category 5 hurricane, with wind speeds of 325km per hour (kph).
Fights have been suspended and the prime minister has urged people to seek shelter from the storm, expected to be country’s most powerful on record.
After twice drenching outlying islands in nearby Tonga last week, Cyclone Winston reintensified on Saturday and was bringing winds of 230kph, with gusts of up to 325kph as it moved west towards Suva, Fij’s capital.
Al Jazeera’s Senior Meteorologist Richard Angwin said Winston would be the “most powerful storm to hit the island state in recorded history”.
“Every one of Fiji’s islands will feel Winston’s effects,” he said.
Netani Rika, a journalist, told Al Jazeera from Suva it was unclear how much damage Winston had done to the island.
“We are told that Winston is heading now to sea and the worst for our area is pretty much over,” she said.
“But I think it won’t be until the sun is up before we are able to see the extent of devestation left by this Category 5 storm.”
Frank Bainimarama, the prime minister, earlier urged Fijians to prepare themselves for a “terrible event”, the Australian broadcaster ABC reported.
“We cannot afford to be complacent,” it quoted Bainimarama as saying.
“And I am especially concerned that some people in urban areas do not appear to have heeded the warnings about the seriousness of the threat.”
The Fiji Times reported that Suva lost electricity before Winston made landfall.
A nationwide curfew took effect across the country from 6pm.
The government also issued a list of 758 evacuation centres across the nation of just under 900,000 people.
“[The curfew] has been in place for the last seven hours now and will remain in place until police give the okay once the emergency services say that it’s safe,” Rika told Al Jazeera.
Airlines Virgin and Jetstar suspended flights into and out of Fiji’s international airport at Nadi, the third largest city, while the national carrier suspended all flights.
Fiji is an archipelago of more than 300 low-lying islands prone to sea surges and flash-flooding.