The National Hurricane Center designated Potential Tropical Cyclone One-C about 1,000 miles east-southeast of Honolulu, and the system could bring Hawaii weather tropical storm conditions this week. It was expected to strengthen into Tropical Storm Hernan by Friday at the latest, with heavy rain beginning on the Big Island the same day.
At 11 a.m. EDT Wednesday, the system’s estimated minimum central pressure was 1003 mb, or 29.62 inches of mercury. Rainfall totals of 5 to 10 inches were possible across much of the Hawaiian Islands, and some spots could see up to 20 inches.
Big Island and the weekend
Heavy rainfall was expected to move into Maui by the beginning of the weekend, then continue through much of the rest of the Hawaiian Islands throughout the weekend. The biggest threat was heavy rainfall and the potential for life-threatening flooding and mudslides, especially across mountainous areas.
Gusty winds could knock down trees and power lines. The National Hurricane Center said the system was likely to be a strong tropical storm as it moved over or near Hawaii, but landfall as a hurricane was not out of the question.
Eastern Pacific pace
The Eastern Pacific had seven named systems so far in the season, and the eighth named system typically forms by August 21. If Hernan became a named tropical system by the end of the week, the season would be running about nine days ahead of schedule.
That faster pace comes after only two of the seven named storms became hurricanes, Fausto and Genevieve. The Eastern Pacific was in its first peak of hurricane and tropical storm activity, with the second peak usually around the beginning of September and the third toward the end of September.
Hurricane Hone in August
The most recent tropical cyclone to directly affect the main Hawaiian Islands was Hurricane Hone in August 2024, when it passed within about 50 miles south of South Point on the Big Island on August 25, 2024. According to NOAA Historical Hurricanes Tracks, only two named storms have made landfall on the island of Hawaii at tropical storm strength.
For residents and visitors, the practical window is now: rain on the Big Island on Friday, Maui by the beginning of the weekend, and a broader stretch of wet weather across the islands after that. The higher totals are most likely to fall where terrain forces rain upward, and that is where flooding and mudslide risk rises fastest.
