What is your hybrid tea David ? Blooms come in all sizes perhaps it is the nature of your rose.

Did it previously have larger blooms?

All of the above!

It's most probably the summer heat. I was very surprised about the difference between spring and summer bloom size. For me, the real party is in the Spring before the South turns into a humid oven. After that, it's a bit of meh. Not only is the bloom more sparse but also much smaller.

I am not sure how long roses bloom into the Fall here but I have a neighbor who said she has a rose that blooms in December. so maybe I will get to see nicer flushes in the Fall.

I think you are right. We had a couple of weeks with no rain and 95 degree heat every day.

I watered them deeply every few days but I think the heat was too much for them.

Guess it is time to stop fertilizing them too.

You don't have to stop fertilizing them now. And if you use organics, like alfalfa or fish emulsion, you can do those any time of year. I use fertilizer right up to dormancy. I would stay away from granular slow release fertilizers but liquid foliar ones are fine.

Ever use this on your roses Urban Farm Fertilizers Rose Garden Professional Rose Fertilizer. 1 Gallon. Makes 256 gals.

by Urban Farm Fertilizers

Caution: I should have noted that you should never use any foliar sprays in high heat! It should be in the low 70s and preferably a cloudy day to spray your rose leaves with fungicides, insecticides or fertilizers, even organics.