Has anyone had a Temecula wine ? It gets very hot down there. It must affect the sugar content adversely.
For growing grapes to make Cabernets and Shiraz, heat is actually a good thing. That's why Napa Valley (further inland than Sonoma and very hot at the north end of the valley, routinely above 100 during the summer) has the best Cabs and Paso Robles (even hotter than Temecula, slightly hotter than the northern Napa Valley) some great Shiraz (and Zinfandel).