7:50 p.m.As winemaker Sal DeIanni pressed just-picked chardonnay grapes into a bladder press at Truchard Vineyards in Carneros on Friday, crews picked fruit in nearby vineyards along Old Sonoma Road ahead of this weekend’s storm.

Thursday and Friday were particularly busy days at the winery, as crews brought in zinfandel and chardonnay, varietals that will suffer if the rain strikes them this late in the season. Cabernet sauvignon, with thicker skins on the berries and looser clusters of grapes to allow drying without mold, are less susceptible to rot.

“Everyone is scrambling,” said DeIanni, as he, assistant winemaker Abraham Alvarez and intern Michael Lucia watched clear juice flow from the press.

The Truchard’s 270 acres produce 10 varieties of grapes for the family’s estate wines and a dozen other Napa wineries.

Harvest began in late August with pinot noir, and should be sewed up by mid-October, co-owner Jo Ann Truchard said.

Yield is down about 30 percent this year as a result of last spring’s unusual frost, but the quality is  excellent, Truchard said.

Her husband, Tony, who left medicine to concentrate on the family business three decades ago, also seemed pleased with the harvest.

“It’s been good so far,” said Truchard, as he watched crews bring in cabernet sauvignon for the Robert Mondavi Winery, the first cab of the year for Truchard.

Around the valley other grapegrowers also reported lower-than-normal yields.

Vince Bonotto, vice president at Diageo Chateau and Estate Wines, owner of several local wineries, said Upvalley cabernet is still out. Other varietals, including petit verdot and cabernet franc, have been harvested.

Overall, he said, “quality has been very good.”

Julie Nord, whose family farms about 1,000 acres in Napa County, including Yountville, Pope Valley and near American Canyon also said that fruit quality is excellent, with good acid-sugar balance.

Yield is 30 to 40 percent below normal, said Nord, who reported heavy frost damage this spring.

Nord’s harvest, which began Aug. 13, is about 70 percent done.

As happened elsewhere in the valley, Nord crews worked hard this week to pick grapes susceptible to be damage by the rain, including syrah and petite sirah.

“We have been picking like crazy,” Nord said Friday.

Up in Chiles Valley, several hundred feet of above the Napa Valley floor, Volker Eisele said he has not begun to harvest any red grapes.

Ripening has been slow, said the proprietor of Volker Eisele Vineyard. “That is good for quality.”

White grapes came in about a month ago, he said.

Eisele, who expects harvest to be over in four weeks, predicts overall tonnage will be “way down” this year. All indications are for a harvest of “extremely high quality and disappointing quantity,” said Eisele, who said the weekend forecast for rain doesn’t worry him.

Sander Scheer, viticulturist at the Hess Collection, which owns vineyards on Mt. Veeder, American Canyon and Pope Valley, said the weekends rains will be OK as long as the weather quickly warms up afterwards to dry the berries and prevent rot.

While the chardonnay from American Canyon vineyards along Highway 29 is 90 percent picked, harvest has barely begun at Mt. Veeder and Pope Valley, he said. Harvest should be completed in early November, Scheer said.

The crews will spend a lot of time on Mt. Veeder to make sure that erosion controls are in place where Hess Collection is replanting a third of its 300 acres, he said.

National Weather Service forecaster Diana Henderson on Friday predicted up to 1.5 inches of rain for the North Bay between Friday through Saturday evening. The last significant rains were in May.