The most important part of watering is to insure that you are getting the soil wet to a depth of at least 12 inches (18 inches is better). The best way to do that is to get a soil probe (Hydroscape has some nice ones). This is a tool that is shaped like a “T”, is usually stainless steel & hollow and comes in a variety of lengths.
Give your roses what you think is a good soaking, wait about 30 minutes, then push the soil probe (with a twisting motion) into the soil about 1 foot way from the center of your hybrid tea rose. After you pull the probe out, look at the soil sample, the entire sample should be moist. Repeat this process in a couple of areas around our garden to check of good distribution. If the soil samples are not moist, then you need to get more water into the root zone.
Do this test in April and it will give you a good idea of how much your roses need in average weather. When summer comes, increase the amount of water and recheck your soil. Finally, never overhead water the roses in the afternoon, this can lead to mildew and other diseases.