With our recent higher temps I have been watering every other day for 20-30 minutes per zone.

Very bad idea ... you are overwatering by a phenomenal amount.

Go to this site and follow the instructions: http://ag.arizona.edu/azmet/phx/

I agree with lzygdns. When it was above 100 I shifted to 15min 2x/wk. I have
a mix of hybrid and reg bermuda and it looks fine on that amt of water. When
I up it for the "real" summer, I'll up the time to insure I get a good deep soaking but probably not the freq. Put some cups out to check the water each zone is receiving. The browning one could be receiving a different amt of water.

Spring transition can be an unsightly time for turf. Sometimes the rye will die before the Bermuda begins to grow vigorously leaving brown patches. The rye planted last year prevents the Bermuda from coming back as early or as strong because it competes for light and nutrients. Other times the Bermuda has been so stressed by the overseeding process that bare patches appear after the rye dies.

Here are steps to help with spring transition to Bermuda from the U of A Karsten Turfgrass Research Center.
� Start your transition only when the minimum nighttime temperature is 60�F or higher for five days in a row - usually mid-April in Phoenix.
� Lower the mowing height of your lawnmower. This is critical to success. If you have standard Bermuda or one of the hybrids like EZ Turf, Midiron or Bob Sod set your mower at 1-1/2 inches. The golf-green type hybirds like Tifway or Tifgreen can be mowed shorter. Do not scalp your lawn as this will damage the grass. Continue this height for four weeks and then return to the normal mowing height for your Bermuda.
� Consistently water to a depth of 8 inches. You can check with a probe or long screwdriver to see how far down the moisture goes. It's easy to probe in moist soil but extremely difficult when you reach a depth where the soil is still dry. Water once every 4 - 5 days through May and once every 2 - 3 days from June to September applying about 3/4 inch of water each time.
� Fertilize your lawn monthly starting the second week in April, with 1/2" lb. nitrogen (N) - per 1000 ft2 . If you use a product like ammonium sulfate (21-0-0) which is 21% nitrogen, you would use 2.38 pounds per 1,000 sq. ft. of lawn. (The calculation is 1/2 lb (or .5 lb) divided by the percent of nitrogen - in this case .21 - that equals 2.38 pounds).

Areas with bare soil can be 'spot-seeded' or sodded with Bermuda in summer if necessary.

Here is a link that might be useful: Turf Tips