When and How Oftem to water grape vines?

Question

I have a few wine grapes and wish to know WHEN it is best to water them.  Presently, the vines are finishing the bloom phase and setting the grapes.  I am in Sonoma County CA and it has not rained for over a month but the ground is deep and has sufficient clay in the soil to retain moisture; the vines are growing well now and show No Stress.

Last year, I watered twice:  once in late Spring and again in mid-Summer (after veraision).  Waterings are always Deep, so as to saturate the root zone.

What do you think?

Thank you.  Russ