A flash-flood watch issued for all islands by the National Weather Service is in effect until this afternoon, but the threat of heavy showers was expected to diminish by the weekend.

An area of heavy showers was about 40 miles south of O'ahu last night and moving to the northeast at about 20 mph.

Maui County and the Big Island appeared to be the best candidates to receive heavy rainfall, the weather service said.

An upper-level trough was moving toward the southeast from Kaua'i at about 35 mph, acting as a destabilizing factor in an atmosphere heavy with low-level moisture. The trough is expected to pass east of the Islands by tonight.

As of 8 p.m. yesterday, Maui's West Wailua Iki rain gauge was the fullest, with a six-hour rainfall total of 4.12 inches.

On the Big Island, Laupahoehoe and Pahoa each had more than 1.2 inches of rain, while on O'ahu, the Windward side showed 1.64 inches in Maunawili and 1.08 inches at 'Ahuimanu Loop.