Dive Brief:

• Hawaii's main electric utility is warning of extended power outages as residents brace for the impacts of Hurricane Lane, the strongest storm to threaten the state in two decades. 

• Lane is expected to bring high winds and torrential rain to areas of the Big Island, Maui and Oahu as it passes southwest of the state as a category 3 storm on Friday and Saturday. The Big Island is already seeing "catastrophic" flooding, the National Weather Service said, after parts received more than 30 inches of rain. 

• The intensity of the storm will likely knock out power, Hawaiian Electric (HECO) said, and customers should "plan ahead for the possibility of extended outages." Experts are also concerned the slow-moving storm could disrupt fuel deliveries or petroleum refining in the state, which relies on oil for much of its electricity generation.

Dive Insight:

Hawaii's isolation puts it energy systems at special risk for disruption from storms like Hurricane Lane. The category 3 storm is expected to skirt south of the island chain this weekend with winds above 90 miles per hour.

Even if the state avoids a direct hit, the National Weather Service says Lane will be a "long-duration event," that could bring heavy rain into early next week, potentially threatening fuel deliveries to the state.

Hawaii generates nearly 70% of its electricity with petroleum, which must be refined at one of two facilities on Oahu. If the storm damages those refineries or receiving points on other islands, generators could run short of fuel.

Even if deliveries are not affected, Hawaiian Electric customers will likely experience power outages due to grid damage, particularly on the Big Island and Maui.

The utility's transmission and distribution system is relatively fragile and exposed on parts of those islands — a single radial line, for instance, carries power from population centers in Maui to the resort town of Hana on the opposite side of the island.

High winds and flying debris are likely to affect power lines like those, HECO said in a Thursday statement. Additionally, NWS warns that flooding and storm surge from Lane could "lead to inundation and overwash" of coastal areas, threatening power infrastructure and port facilities.

Hawaiian residents have more distributed generation per capita than any other state, but it won't help most of them through the storm. About one in five Hawaii households have rooftop solar, but relatively few have installed the battery backup necessary to operate independent of the grid.

HECO said Thursday it is working with the Western Regional Mutual Assistance Group, a group of utilities that share workers and equipment, to prepare for impacts of the storm. Experts say the failure to activate mutual assistance agreements is one of the main reasons storm recovery took so long after the Hurricane Maria destroyed Puerto Rico's utility system last year.

This week, Lane became only the second category 5 hurricane to threaten the island before weakening to a category 3 on Friday. The other was Hurricane John in 1994, which passed wide of the islands and caused little damage. Experts say a climate change contributes to the intensity of hurricanes and that utilities will have to deal with stronger storms as the planet warms.