Some voters may have been eager to get outside. Hawaii Electric Light said more than 9,000 customers remained without power in numerous cities and towns after Iselle, the first tropical storm to hit Hawaii in 22 years, glanced by the islands without causing any major injuries, Gov. Neil Abercrombie said.
Iselle has passed and has been downgraded to a post-tropical cyclone, but the window for voting is still narrow, because Julio remains a Category 2 hurricane with winds topping 100 mph.
Read MoreHawaii rattled by quake as hurricanes near
While Julio is expected to remain north of the islands when it approaches Sunday night, it will still come pretty close, and residents and business should "watch for developments with this system closely," the National Weather Service said.
—By M. Alex Johnson, NBC News