Sammy, to play with the answer a bit, it's a matter of both degrees and degree. That is the actual temperature and length of exposure.
Problems with wine are referred to as "wine faults" and among them is heat damage, often referred to as "cooked wine". Several things happen when wine is exposed to heat. One is that it expands, like any liquid. This puts the bung (or cork, for bottled wine) under pressure, eventually resulting in oxidation. Beyond that, subjecting your wine to heat causes a baked smell and flavor. The wine will turn brown.
Cooked wine can occur fairly quickly (perhaps by keeping a bottle in the car for a Summer day) or by exposure to lower temperatures over an extended period (such as what could occur in your situation). I am not familiar with any reliable studies on the subject, so can only suggest you avoid anything higher than 75F for extended periods.
One last point, dramatic temperature changes compound the temperature issue and should be avoided.