Storms of that strength, classified as a Category 3 on the Saffir-Simpson hurricane wind scale, are considered capable of causing devastating damage to populated areas.
It had maximum sustained winds of 130 miles per hour and moving at 12 miles per hour.
Hurricane Hector strengthened to a Category 3 hurricane Friday with maximum sustained winds of 120 miles per hour.
Hawaii emergency officials are keeping track of a hurricane that's expected to pass to the south of the islands this week.
The Kilauea volcano has spewed lava and molten rock into neighborhoods in Hawaii's Big Island for three months.
Hurricane Hector became a Category 4 storm for a few hours early Sunday but then dipped back to Category 3, still a risky force, as it headed across the Pacific, threatening to hit Hawaii's Big Island and possibly its active volcano, officials said early Sunday.
The US National Hurricane Centre is urging people in Hawaii to prepare for its arrival in the coming days.
The Center said high surf and rip currents will be the main threat on beaches and some bands of heavier rain would hit the islands.
Hurricane-force winds extend outward up to 30 miles from the center and tropical-storm-force winds extend outward up to 105 miles, the National Hurricane Center said.
Tom Travis, Hawaii's emergency management administrator, said: "Hector is our first hurricane this year".
The current Kilauea lava flow from one of about two dozen volcanic fissures that opened in the ground has been going on for 93 days, making the longest non-stop eruption on record from Kilauea's lower East Rift zone.
"However, Hector is expected to still be a major hurricane when it moves into the central Pacific basin", according to the NHC.