Potential rain in Hurricane Hilary’s wake worrisome for Sonoma County winegrowers

As Hurricane Hilary moves along the western coast of Mexico and flirts with the coastline of California, winegrowers in Sonoma and Napa counties are keeping a close eye on the weather forecast.

The storm has the potential to bring heavy rains and high winds to parts of the state over the weekend and into next week, which many winegrowers find worrisome at this critical time.

This year’s cool growing season has delayed harvest by an average of three weeks, and most fruit is still on the vine. Cooler temperatures have also made some vineyards more susceptible to disease, which wet weather could exacerbate.

“If there are any disease pressures in the vineyard — like powdery mildew — the rain and wind will spread it,” said John Balletto, president and founder of Balletto Vineyards in the Russian River Valley. “That would not be good.”

While it’s still too early to predict Hilary’s impact in the North Bay, winemakers like Adam Lee of Clarice Wine Co. have been tracking the forecast through the National Oceanic and Atmospheric Administration (NOAA), which provides several potential weather scenarios.

“Given we’re a long way out from harvest, a single rain may or may not lead to problems,” Lee said. “Rain can deposit mold spores (botrytis) in the vineyard, so its effect can depend on whether a vineyard has an open canopy (to increase air flow) and if it’s on top of its spray program.

“But a single rain does mean you have one strike against you, he added. ”Oftentimes, you don’t get more than two strikes when it comes to grape growing.”

Stephanie Honig, co-vintner of Rutherford’s Honig Vineyard & Winery, said her winemaker, Ashley Eglelhoff, is monitoring the movements of the hurricane closely, also through NOAA.

“Our plan is to move forward with picking sauvignon blanc grapes on Tuesday,” Honig said. “Worst-case scenario is that if it gets really moist, our tractors won’t be able to run. The rains could also cause some mildew, but we’re not making any adjustments at this time.”

Acknowledging “it looks like quite a storm,” Jon Ruel, CEO of Napa’s Trefethen Family Vineyards, said he’s keeping an eye on the forecast but he’s not overly concerned at this point.

The brunt of heavy storm activity over land is expected across parts of Southern California, including the San Diego and Los Angeles basins, the interior desert and parts of the Sierra Nevada.

“We’re expecting the energy to diminish considerably by the time it gets up here,” Ruel said. “It will probably just be enough to settle the dust on the vineyard avenues. But even if it’s more, the grapes are looking great so far this year and they can handle a spot of rain, especially if the sun comes out right after.”

However, Ruel said, other regions may be in for some challenges.

“Even if downgraded to a tropical storm by the time it hits Southern California, it would be the first time since 1939,” he said.

That tropical cyclone, nicknamed El Cordonazo or the Lash of St. Francis, hit Long Beach and San Pedro in September, with gusts up to 65 mph, heavy flooding that killed 45 people across Southern California and an additional 48 people at sea, according to the Los Angeles Times.

Southern California authorities were bracing for the storm Thursday, raising the alarm over a forecast that called for potential record August rainfall, starting Sunday, dangerous flash floods and rough surf.

You can reach Staff Writer Sarah Doyle at 707-521-5478 or sarah.doyle@pressdemocrat.com. On Twitter @whiskymuse.

You can reach Wine Writer Peg Melnik at 707-521-5310 or peg.melnik@pressdemocrat.com. On Twitter @pegmelnik.