A tropical disturbance east-southeast of Hawaii is expected to strengthen into a tropical storm before nearing the islands late Friday, prompting forecasters to warn residents to prepare now for potentially dangerous winds, heavy rain, flooding and large surf.
The Central Pacific Hurricane Center designated the system Potential Tropical Cyclone One-C early today, with the disturbance about 935 miles east-southeast of Hilo and 1,140 miles east-southeast of Honolulu. It was moving west at about 10 mph with maximum sustained winds of 35 mph.
The system had a 90% chance of developing into a tropical cyclone within 48 hours and over the next seven days, forecasters said. A tropical storm or hurricane watch will likely be needed for portions of the Hawaiian Islands by early Thursday.
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The system is forecast to move west to west-northwest over the next several days, with its center nearing the Hawaiian Islands by late Friday. The exact track and strength remain uncertain, and forecasters said the severity and location of the impacts will become clearer as the system becomes better organized.
The National Weather Service in Honolulu said the system could bring 5 to 10 inches of rain across much of the island chain, with maximum totals of 20 inches possible. The rainfall could cause life-threatening flooding and mudslides, particularly in areas of steep terrain.
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Hawaii island and Maui County currently have the highest potential for heavy rainfall, although that forecast could change as the system develops.
Strong winds are also possible, with the NWS warning that damaging winds could affect the islands even if the storm’s center remains offshore. The latest state forecast calls for tropical storm conditions to be possible as early as Friday night on Hawaii island and across much of the state Saturday and Sunday.
For Saturday, the state forecast calls for very windy conditions, with northeast winds of 30 to 45 mph across Kauai, Oahu, Maui, Molokai and Lanai. Hawaii island could see southwest winds of 30 to 45 mph.
The system is also expected to generate a large easterly swell as it moves northwestward across the Central Pacific. Surf could build along east-facing shores from east to west, with warning-level surf of 15 feet or higher possible this weekend.
The NWS also has a small craft advisory in effect through 6 p.m. Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Hawaii island leeward waters and Hawaii island southeast waters. Northeast winds of 15 to 25 knots are expected in those areas.
Forecasters said fire weather concerns could also increase Friday as winds strengthen and a dry, stable air mass moves over the islands. The combination of lower humidity and stronger winds could create near-critical fire weather conditions.
For today, mostly sunny conditions are expected statewide, with scattered showers focused on windward and mauka areas. Highs will reach 86 to 91 degrees, with east winds of 15 to 20 mph.
Thursday will be partly cloudy and breezy, with isolated to scattered showers in windward and mauka areas. Highs will be 86 to 91 degrees, with northeast winds of 15 to 25 mph.
Friday will remain partly cloudy and breezy, with scattered windward and mauka showers and a chance of leeward showers at night. Highs will reach 86 to 91 degrees, but tropical storm conditions will be possible Friday night, particularly on Hawaii island.
Saturday could bring the first significant impacts from the developing system, with tropical storm conditions possible statewide. The forecast calls for mostly cloudy skies, very strong winds of 30 to 45 mph and showers, with locally heavy rainfall possible. Highs will be 86 to 91 degrees.
Sunday also could bring tropical storm conditions, with windy weather, widespread showers and locally heavy rainfall. Highs will range from 85 to 90 degrees, with winds shifting to the southeast and reaching 20 to 35 mph in much of the state.
The NWS urged residents and visitors to prepare now for potential tropical cyclone impacts this weekend and continue monitoring updates as the system develops.
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For information about storm preparation, go to honolulu.gov/dem.