"Lane is expected to produce total rain accumulations of 10 to 15 inches with isolated maximum amounts of 20 inches over the Hawaiian Islands", the Central Pacific Hurricane Center said.
The National Weather Service said in a statement: "Lane is forecast to pass near the Hawaiian Islands this week, potentially bringing dangerously strong winds, rough seas and large swells".
Although it is not certain whether the storm, packing peak winds of 150 miles per hour, will directly strike the islands or just graze them, significant effects from rain, wind and waves are becoming increasingly likely.
A slow weakening of Lane is expected over the next two days but the system is expected to remain a unsafe hurricane as it draws nearer to the islands, the weather service said.
Forecasters warned of large swells that could produce unsafe surf and strong currents along some shorelines. "If the storm were to make a significant impact on the island of Oahu, in particular, it could cause flooding at Honolulu International Airport, the oil refinery at Barbers Point, and several large military installations, including Joint Base Pearl Harbor-Hickam", it noted.
A hurricane watch means that hurricane conditions are possible within the watch area.
A look at the path for Hurricane Lane as seen on Tue., Aug. 21, 2018. The proclamation also authorizes the expenditure of state monies as appropriated for the speedy and efficient relief of damages, losses, and suffering resulting from Hurricane Lane.
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Landfalling hurricanes are very rare in Hawaii, as the Central Pacific does not normally see as many storms as the Atlantic or Eastern Pacific, and the Hawaiian Islands present a very small target in the vast Pacific Ocean.
The gas lines were long at Costco in Kahului on Tuesday as Hurricane Lane approached the Hawaiian Islands.
Hurricane Lane poses a "potential threat to life and property", according to the NWS, and "efforts to protect property should now be underway".
"Due to a continued high degree of uncertainty on the forecast track and intensity of Lane, hurricane impacts could be felt across any of the Hawaiian Islands".
More watches and even warnings could be necessary for additional islands as the storm moves closer in the next 24 to 48 hours.
The Hurricane Center urged residents of Hawaii to prepare for the storm.