That much rain could be making your leaves turn yellow, at least that's what happens to my roses when we have too much rain.

Yellowing leaves is a symptom of both over and under watering. Since you can't control the rain all you can do is make sure the soil the rose is in drains properly. If there is a lot of puddling on the ground around the rose that does not drain off quickly you might want to check deeper and see if the ground is staying soggy wet for too long. Heavy clay soils don't drain well. Amending the soil may will help with drainage.

Thanks.

I would add some granular humic acid around the soil line -- to improve the soil, especially the drainage. Check that water really has someplace to go after a puddle maker, (most important), and then try to break up the soil some with humic acid, sometimes called Leonardite. You can probably get Humic Acid at an ag store near you, or else, but more expensively, online.