It sounds to me like you have Alternaria Blight. It is caused by the fungus Alternaria cucumerina, and infects melon, squash, cucumber, pumpkin, and watermelon. Wet weather and temperatures of 60-90 F are it's best conditions. Spots develop first on older leaves. They enlarge rapidly and turn light brown or dark brown to black. Spots on the upper leaf surface may develop rings, Rapid defoliation occurs when weather favors the disease.
I have had this on my cucumbers before, and the only biological thing I found to treat it was to spray with copper hydroxide. This did slow the blight considerably and I was able to harvest cucumbers.
Once you have harvested, ensure that all foliage and plant material is burned, and then once again spray the garden area with copper hydroxide. It is a fungus that can lie in wait for it's perfect conditions, so try to eradicate any thing left behind.
You are correct in assuming that the weather has contributed to this, and there was probably nothing you could do to prevent it.
Best of Luck!