Batten down the hatches!

Some mighty powerful storms are coming to Napa County, promising heavy rains and howling winds starting tonight.

Downpours, very heavy at times, are set to hit late tonight, according to Diana Henderson, National Weather Service forecaster.

“We are looking at up to five inches of rain in some places,” said Henderson.

“The rains will be accompanied by very strong winds,” Henderson said. “We have issued a high wind watch for the area, including Napa County.”

Friday will bring the stormiest conditions, she said, and Mother Nature will ease up starting Saturday. “Showers are still in the forecast, but the strong winds and heavy rains should be on the way out by late Saturday. We should pretty much be coming out of the worst of it by Sunday morning.”

Although Neal O’Haire, Napa County emergency services manager, isn’t downplaying the strength of the impending storms, he doesn’t foresee major flooding problems.

“This is a classic storm,” he said. “We may see some local flooding in Napa from the small streams. There is a chance of up to eight inches of rain predicted in the hills. That’s a lot of water,” he said. “But at this point, we are not worried about the river overflowing its banks. If we had three of these powerful storms in a row, we could be looking at flooding.”

O’Haire said the storms are complicated by the whipping winds, which could get up to 40 miles per hour on the valley floor. There will be heavy gusts on the mountain ridges, with winds predicted to top 75 miles per hour above 3,000 feet. “That is hurricane wind,” he said.

The county’s River Forecast Center predicts significant rises in the Napa River, but only about halfway to monitoring stages.

The ground, which is relativity dry, will be saturated by the storms, O’Haire said, adding that future storms could produce more runoff.

Lake Hennessey is currently about 21 feet below the spillway, and Milliken Dam is 12 feet below the spillway.

“Although the storms will be intense, they are good news for Napa County’s water supply,” O’Haire said.

The heavy rains could lead to slides and flash flooding in small streams in such areas as Mount St. Helena, Mount Veeder, Petrified Forest and Atlas Peak roads. O’Haire urges those living along the small streams to monitor the rainfall and keep an eye out for flooding and slides.

Henderson also urged motorists to be extra careful driving in the bad weather.

“The roads will be wet and the winds will be very strong. There could be a lot of puddling and ponding on the roadways,” she said. “These conditions can make driving hazardous.”

With the high wind warnings, there is also a strong potential for power outages stemming from trees blown into power lines and down wires.

Sandbags will be available this Saturday at the city of Napa corporation yard on Jackson Street, and the county corporation yard on Silverado Trail, just south of the Yountville Cross Road.

There is no charge for sand bags. People are urged to bring their own shovels.