Wines I'm Making: 2013 Cabernet at 20 Brix

Yesterday I got out the refractometer for the first time this year--out of curiosity; we are still several weeks from a normal harvest date--but a random berry I tested from one of our Cabernet vines was at 20 brix. I normally aim to harvest at around 24 brix. As generally it takes about a week of good weather to raise the brix level by one degree, that would suggest we're about a month from harvest. As we usually harvest in the first week of October, everything seems to be on track, despite the rather cool summer we've had. Looking at the grapes, I noticed some that were beginning to shrivel a little. I'd watered only once so far this year. Given the cool weather, I was trying to see if we could go entirely without supplemental water this year, but I decided it would be best to water once before harvest. I turned on the irrigation system for five and a half hours.