I commuted 40 miles (roundtrip) a day last year through Tempe and Mesa all summer (and the rest of the year too). Most days were not a problem if I just had two water bottles (one frozen). On the especially hot days I would soak my jersey and ride it until dry, then stop at a park and re-soak it. I found with this method I could get up to 115 degrees and above for an hour and a half and be ok. Another thing is to slow down a bit when they have heat advisories as overdoing it can get you in trouble on hot days. Incidentally a soaked jersey will dry out in 10 - 20 minutes of riding on hot days. My one way commute is longer now so my evening commute is just 4 miles over to my father in-laws place of employment to get a ride home so this summer I won't have to do that much heat riding.