The drenching northern fringe of former hurricane Cosme swept across the Big Island overnight, and was expected to bring rains to the rest of the state today and tomorrow.

Big Island residents were bracing for between 5 and 10 inches of rain overnight and today. An islandwide flash-flood watch is in place through this afternoon.

Parts of the Big Island were getting moderate to heavy rain as of 8:45 last night, but there were no reports of road closures or property damage, civil defense official Neil Gyotoku said.

A second band of heavy showers was expected about midnight, he said.

From 5 to 8 p.m., Glenwood received 1.9 inches of rain, Laupahoehoe 1.78 inches and Hilo airport 1.73 inches.

Big Island civil defense chief Troy Kindred said his office stepped up monitoring and was getting regular surf and rainfall reports from police and fire officials.

"We definitely have some (storm) cells offshore and along" the eastern and southern parts of the island, Kindred said earlier yesterday.

County crews have cleaned out drains and culverts to minimize flooding and have filled sandbags in case they are needed. The key for the island is whether the rain is spread out or falls in a short period of time, which could cause flooding, he said.

Other islands can expect moisture as well, but less of it — perhaps up to 5 inches in parts of Maui County and up to 2 inches on O'ahu and Kaua'i.

"It will resemble more wet trade-wind weather," said National Weather Service meteorologist Bob Burke.

Winds could gust to 45 mph atop the Big Island peaks and Haleakala on Maui, and in areas like South Point and 'Upolu Point, whose terrain generally promotes strong and gusty winds.

At 5 p.m. yesterday, Cosme was 225 miles south of Hilo, moving west at 20 mph. Winds near the center were 35 mph, gusting to 45 mph.

High-surf advisories are in place for eastern shores of all islands, with predictions of 8 to 10 feet on the Big Island and 6 to 8 feet on other islands. Small-craft advisories were in place for all Hawai'i waters through tonight and for Big Island southeast and leeward waters through Monday.

Cosme is expected to have moved west of the islands by the end of the weekend. It could enter warmer water Monday and intensify to sustained winds of near 40 miles an hour, but that should have no effect on Hawai'i weather.

The tropical depression is the first named storm to enter the central Pacific this hurricane season. It reached hurricane wind speeds early this week, but then lost strength from passing over cooler water.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.