The North Coast grape harvest, which began Aug. 1 in Napa Valley with fruit for sparkling wines, has now progressed into grapes destined for still wines, the vast majority of the region's grape crop. Fruit is ripening faster in warm regions like Dry Creek Valley, leading to an unusually early start to harvest in hot spots.

In his 35 years harvesting grapes from the same vineyard, David Coffaro, owner of the Geyserville winery that bears his name, said crush has started this early only four or five times.

"I think we're a little heavier than normal," Coffaro said, indicating that he thought the harvest would be larger than normal. "I think the bunches are sizing up very good."

Grape growers and vineyard managers said they are expecting a crop that's perhaps a little larger than normal, but probably not as bountiful as the bumper crop of 2012.

"We are excited about the start of harvest 2013," said Honore Comfort, executive director of the Sonoma County Vintners. "We're looking forward to a good year. The report so far is that the yields will be solid, and the quality very high, from across Sonoma County."

Stretches of warm weather did create some mild issues for growers. Some found themselves battling mites in the vineyards, which show up during heat spells and delay fruit ripening. Others found mildew among some clusters after dewy days, although growers said they were able to limit mildew problems by spraying with sulfur or taking other preventive actions.

"The mites will slow things down, but you won't lose anything," Coffaro said. "As far as the mildew, that can be a problem if it gets out of hand, but we didn't lose anything."

Meanwhile, harvest is on hold in cooler regions like the Russian River Valley. Some growers are anticipating an earlier start, but many expect to begin at a normal time.

Pinot noir in the Russian River Valley may be ready for harvest in about a week, said Ashley Herzberg, consulting winemaker for several wineries including Bacigalupi Vineyard in the Russian River Valley.

"Right now we're having pretty foggy mornings ... which gives it a nice hang time and lets the acid levels go down without the sugar going up too much," Herzberg said. "We had so many warm days so much earlier in the season, so everything happened earlier."

In Sonoma Valley, pinot noir grapes also may be ready next week, said Chris Bowen, vineyard manager for Hunter Farms.

"So far, things have looked pretty good," Bowen said. "To me, it's been a real cool summer. We had some really hot days, but overall it's been cooler than average."

Back in Dry Creek Valley, Coffaro's sauvignon blanc grapes were likely headed for a white wine blend at his winery, which produces about 5,000 cases per year. The small amounts of botrytis, a type of mildew that appeared on some clusters, wouldn't interfere with Coffaro's plans for the grapes, he said.

"It's like a raisin, and so there's nothing wrong with that," Coffaro said, indicating a cluster that showed a small amount of mildew. "If it starts rotting, that's like the 'noble rot.' That's going to give some character to the wine, too."