Mostly, we get cool bay breezes at our location on the south end of the Napa Valley but it wasn't enough to moderate the weather. So, what about the vines?
On our way across the Central Valley I saw numerous instances of sunburned grapes -- and many instances without any problems at all. Part of the balancing act for a grapegrower is walking that thin line between a vine "struggling" to produce concentrated, intense wines. On the other end is the big, strong, healthy vine that can take a beating in those conditions. Usually that also includes irrigation in some form here in California, usually a drip system.
The biggest trick for getting the intensity without over watering is a combination of experience and technology. The only way to stave off damage due to excessive heat is by having water in the soil before the event. This takes advance planning which, in our case, is done by our Vineyard manager, Mike Wolf and his great crew. They monitor leaf water potential with a device called a pressure bomb. It measures the amount of pressure applied before the leaf exudes water. With that device and an eye towards the weather forecast, the best vineyard managers (like ours) know when to add water that the vine can use at the proper time to stave off any damage.
The upshot from last week? A few dried up berries here and there on the most exposed location. These will be a non-issue by harvest time, but it does give one a scare. If the timing were later in the season, then the berries and their raisiny flavors can add to the juice. That's not good (unless your trying to make an ersatz Amarone).
Honestly, after 27 years doing this, I find grapevines incredibly amazing plants. We dodged another bullet but there are still several weeks before harvest. I find that I hold my breath a little as we get closer to the crush because nothing is safe until they're in the tank and bad things can happen right up to the last minute (like 1989's rains or 2003's single-digit humidity and north winds for 10 days).
Oh, yea: breathe!