The National Weather Service said Hector remained a category four storm as it moved closer to Hawaii's Big Island.
At 11.30am (Hawaii time) today, the storm was located 1359 kms east of Hilo and forecast to pass to the south of Hawaii, the service said.
Hector continued to move in a westerly direction with winds as high as 250 km at its centre, it said.
The US National Hurricane Centre urged people to prepare for tropical storm force winds across Hawaii County on Wednesday.
Hector could cause high surf on the eastern and southeast-facing shores of the Big Island and East Maui, the centre said.