Hurricane Iselle was forecast to hit Hawaii on Thursday as residents scurried to gather supplies and officials warned of flooding and outages, while a hurricane tracking right behind it was upgraded to Category 2 status, U.S. officials said.

Iselle was about 405 miles (652 km) east of Hilo on the Island of Hawaii at about 11 p.m. Hawaiian Standard Time on Wednesday (5:00 a.m. EDT)and heading west-northwest at 18 miles (30 km) per hour, with maximum sustained winds of 90 mph (144 kph), the Central Pacific Hurricane Center said.

The center of Iselle was forecast to pass very near or over Hawaii's Big Island on Thursday evening and pass just south of the smaller islands on Friday, the CPHC said.

"Some weakening is forecast during the next 48 hours, but Iselle is now expected to be a hurricane as it passes near or over the Big Island," it said.

State officials warned of the potential for flash floods, mudslides and power outages, and Governor Neil Abercrombie signed an emergency proclamation, freeing up funds and other resources, in anticipation of its arrival.

Residents were stocking up on basics as authorities in Honolulu advised them to prepare seven-day disaster supply kits. Shoppers waited in lines at supermarkets with carts full of bottled water, batteries and nonperishable food.

Meanwhile Hurricane Julio, packing maximum sustained winds nearly 100 miles per hour (155 km/h), with higher gusts, has been upgraded to Category 2 status, the National Hurricane Center said on Thursday.

Julio, which was moving west-northwest at about 17 mph (28 km/h), could continue to strengthen on Thursday but was forecast to gradually weaken by late evening and into the weekend, the center said.