Potential Tropical Cyclone One-C is expected to strengthen as it moves toward Hawaii, and the tropical storm weather forecast calls for life-threatening flooding risk beginning Friday. The National Hurricane Center placed the system a little over 1,000 miles east-southeast of Honolulu on Wednesday morning.
Rainfall totals of 5 to 10 inches are possible across much of the Hawaiian Islands, with some spots reaching 20 inches. The heaviest rain is expected first on the Big Island, then Maui by the beginning of the weekend, before spreading across much of the islands through the weekend.
Big Island first, then Maui
The National Hurricane Center said heavy rainfall should begin on the Big Island on Friday. By the beginning of the weekend, the rain is expected to move into Maui, with the rest of the Hawaiian Islands seeing impacts throughout the weekend.
That timing matters for residents and visitors who need to track local conditions as the system approaches. The forecast points to a storm that is still organizing while already carrying a clear rain threat over a broad area.
Hernan and the rain threat
At 11 a.m. EDT Wednesday, the estimated minimum central pressure was 1003 mb, or 29.62 inches of mercury. The system was likely to be named Hernan by Friday at the latest, and the National Hurricane Center said it could strengthen into a strong tropical storm as it moves over or near Hawaii.
The bigger complication is that hurricane landfall was not ruled out. The same forecast also says landfall as a hurricane was not out of the question, even though the main threat was expected to come from heavy rain, flooding, mudslides, and gusty winds that could knock down trees and power lines.
Hawaii and August storms
Only two named storms have made landfall on the island of Hawaii at tropical storm strength, according to the NOAA Historical Hurricanes Tracks database. Hurricane Hone was the most recent tropical cyclone to directly impact the main Hawaiian Islands in August 2024, passing within about 50 miles south of South Point on the Big Island while strengthening into a Category 1 hurricane.
The Eastern Pacific was already at seven named systems, and the eighth named system typically forms by August 21. If Hernan is named by the end of the week, the season will be running about nine days ahead of schedule.
For anyone on the Hawaiian Islands, the immediate takeaway is to prepare for several rounds of rain rather than a single burst. The forecast centers on the Big Island first, then Maui, then the rest of the islands, with the highest totals still possible in the same system that may grow stronger while it approaches.
