Tropical Storm Wali, the first named storm of the Central Pacific hurricane season, formed southeast of Hawaii on Thursday and is expected to weaken but still bring heavy rain over the islands this weekend.

The National Weather Service issued a flash flood watch for all islands from Saturday 6 p.m. until Monday 6 p.m. in anticipation of Wali’s arrival.

"Localized intense rainfall is likely to occur with the potential for flash flooding. The greatest chance of flooding will occur over windward slopes, with a lesser chance over leeward locations," forecasters said.

The weather service said tropical depression One-C reached tropical storm strength about noon Thursday with 45 mph winds and higher gusts. 

By 5 p.m., Tropical Storm Wali was traveling at a rate of 12 mph to the northwest. Tropical storm force winds extend 90 miles from the center of the storm, which was 995 miles miles east-southeast of Hilo and about 1,200 miles from Honolulu.

The storm increased in strength overnight and Thursday and "looks to be moving rather slowly," said weather service meteorologist Ian Morrison. "It has about 12 to 24 hours to maintain itself or strengthen slightly, then will weaken dramatically in the 24-hour range."

Forecasters said the storm is expected to weaken back into a post-tropical depression as its remnants near the islands.

"Expect tropical moisture to come Saturday night through Monday night, with very humid conditions with the possibility of heavy showers," Morrison said.

Rain ahead of the storm is expected to reach the Big Island and Maui Saturday night and the other islands on Sunday.

"Rainfall intensity will increase with the added moisture content and muggy conditions will prevail. Locally heavy rainfall will be possible as models show precipitable water levels over 2 inches (an hour)," a weather service forecast said.

Officials at the Hawaii Emergency Management Agency, formerly known as State Civil Defense, said they, along with the county civil defense agencies, are closely monitoring the storm. HI-EMA encourages members of the public to be alert and to take appropriate precautions.

"We recommend residents and visitors take the time to prepare and be informed," said Doug Mayne, administrator for Emergency Management. 

The Central Pacific Hurricane Center is tracking Wali and issuing advisories on the storm.

According to the Hawaiian Dictionary, wali means "smooth, thin, as poi." It also has a second meaning of "supple, limber, as a dancer’s body."