Tropical Storm Flossie, the sixth named storm of the Pacific hurricane season, was on a track to take it directly over Hawaii, where authorities issued an alert for "torrential" rains and dangerous flash floods early next week.
Flossie formed without a lot of notice Wednesday in the open waters of the Pacific. But it strengthened Thursday night, and by 8 p.m. ET Friday, it was packing 60-mph maximum winds.
The storm was about 1,350 miles east-southeast of Hilo, moving west at 20 mph. It's expected to turn slightly northward over the weekend — on a heading straight for Hawaii, arriving late Monday or early Tuesday.
Satellite images Friday afternoon showed a well-organized storm with a sharply defined, compact eye spinning tropical storm-force winds as far as 70 miles from the center.
It's too soon to know how powerful the storm might be when it arrives. Historically, tropical weather systems lose power as they hit colder waters on their way toward Hawaii, said Jennifer Robbins, a meteorologist for NBC station KHNL of Honolulu.
"It's all about the ocean temperatures," Robbins said. "There could be enough punch for it to cause a whole lot of rain."
The National Weather Service's Honolulu office cautioned that "specific timing and intensity of impacts remain uncertain due to errors in track and strength."
But it said "there remains a chance of the system remaining a tropical storm" and even a 5 percent chance that it could grow into a hurricane.
Hawaii State Civil Defense issued an alert Friday evening warning of the possibility of "torrential rainfall, thunderstorms and high winds."
"Flooding may occur rapidly and threaten life and property," it said. "Ground saturation caused by the heavy showers increase the danger of flash floods, mudslides and rockslides."