A tropical storm warning is issued when there is a high probability of tropical storm force winds expected anytime within the next 36 hours.
Swells kicked up by Hector are expected to reach shores of the Big Island and Maui late Tuesday, "likely becoming large and unsafe by late tonight and Wednesday", the Central Pacific Hurricane Center in Honolulu said.
The storm's centre was about 240 miles (385 kilometres) west-southwest of the southern tip of the Baja and moving to the northwest at 15 mph (24 kph).
The fourth storm of the season formed around 11am today about 1,000 miles west of the Azores, but it poses little threat to anything but fish.
The Category Four storm was expected to pass about 165 miles (100 km) south of the Big Island on Wednesday, government forecasters said.
Debby transitioned to a tropical storm Wednesday morning with a greater concentration of storms near its center.
John was centered about 340 miles (545 kilometers) southwest of the Mexican port of Manzanillo early Monday afternoon, with maximum sustained winds of 70 mph (110 kph).
Four tropical cyclones are swirling in the Pacific Ocean this week, at least one of which is a significant threat to land.
Last week finished up with a hurricane and three disturbances in the East Pacific tropics. The tropical-storm-force winds associated with Debby are well removed from the center as indicated by a recent ASCT pass and are occurring within a cyclonically curved band of moderate convection. A gradual turn to the northeast is anticipated thereafter.