The National Hurricane Center has designated a system about 1,000 miles east-southeast of Honolulu, Hawaii, as Potential Tropical Cyclone One-C, and it is expected to strengthen as it moves toward the Hawaiian Islands. Heavy rain is forecast to begin on the Big Island on Friday, with the threat spreading to Maui by the beginning of the weekend and then across much of the rest of the island chain through Sunday.
That timing is why residents and visitors are watching this system closely today. The heaviest rain could reach 5 to 10 inches across much of Hawaii, with some spots seeing up to 20 inches, enough to raise the risk of life-threatening flooding and mudslides in mountainous areas. Gusty winds could also knock down trees and power lines, adding another hazard to a weekend storm that is more likely to drown roads and valleys than flatten them.
The National Hurricane Center said Potential Tropical Cyclone One-C is likely to become Hernan by Friday at the latest, and it is already forecast to be a strong tropical storm as it moves over or near Hawaii. That leaves a narrow but important uncertainty in the track: landfall as a hurricane is not ruled out, even though the main threat remains the rain. Which parts of the island chain take the worst of it is still unknown, but the setup favors the kind of broad soaking that can turn fast when terrain forces moisture upward.
The Eastern Pacific has been unusually active, with seven named systems already this season. If Hernan is named by the end of the week, the basin will be running about nine days ahead of schedule, a sign of how quickly storms have formed in a season that is already deep into its first peak. The most recent tropical cyclone to directly affect the main Hawaiian Islands was Hurricane Hone in August 2024, when it passed about 50 miles south of South Point on the Big Island and its outer bands reached the island. This one is not there yet, but the forecast gives Hawaii little time before the rain arrives and even less room for error if it strengthens faster than expected.
