Hurricane Nolo strengthened into a Category 2 storm Friday as it moved north-northeast south of Hawaii, with forecasters warning of potentially catastrophic rainfall across the Big Island.

An Air Force Reserve Hurricane Hunter aircraft measured maximum sustained winds of 105 mph, according to an 8:35 a.m. HST update from the National Hurricane Center. Nolo was located about 185 miles south of South Point on the Big Island and was moving north-northeast at 5 mph.

A tropical storm warning and hurricane watch remained in effect for Hawaii County, which encompasses the Big Island. Tropical storm conditions were expected to begin Friday night, with hurricane conditions possible by early Saturday, particularly in areas with steep terrain.

Maui County was under a tropical storm watch, with tropical storm conditions possible beginning Saturday.

The eastern and southern portions of the Big Island could receive 10 to 15 inches of rain, with isolated totals reaching 25 inches. The National Hurricane Center warned that the rainfall could produce “catastrophic life-threatening flooding and mudslides,” particularly in steep terrain.

Western parts of the Big Island were forecast to receive 2 to 4 inches of rain, with isolated totals of 8 inches. Maui could see 4 to 6 inches, with isolated amounts of up to 10 inches and the potential for life-threatening flooding and mudslides.

Other parts of the Hawaiian Islands were expected to receive 1 to 3 inches of rain, with isolated totals of 6 inches and possible localized flooding.

Nolo was expected to slow Friday night before turning west-northwest and then west over the weekend while accelerating. Forecasters expected the storm to strengthen into a major hurricane during that period.

Storm surge could push water 1 to 3 feet above ground along portions of the Hawaii County coastline if the peak surge coincides with high tide. Large waves were also expected along the immediate coast.

Swells were forecast to reach exposed east- and south-facing shores of the Big Island Friday before spreading westward and building through the weekend, creating dangerous surf and life-threatening rip currents.