It sounds like it is exposed to the outside temps and this could really be an issue since the fluctuations daily isn't good for it.
This info will help explain why:
Temperature stability is the “holy grail” of wine storage. It is the most important of the storage requirements, and at the same time one of the hardest ones to achieve. For those using home storage methods, a 5ºF temperature variation can be a daily occurrence. Moreover, if you think your wine cabinet, your cellar, or your current storage provider is doing a good job, try leaving a Max-Min thermometer in the unit for a few months. I think you’ll be surprised.
Maintaining constant temperature over time is even more important than the actual average temperature level. Fluctuations in temperature allow more air/oxygen into the wine. As the environment warms up, the wine (and air) in the bottle warms up and expands. The only thing that can give is the cork. Either the cork moves out slightly, or some of the air (or wine when stored on its side) will push past the cork. As the air cools, the contents of the bottle will contract, drawing air/oxygen into the bottle. Over many temperature fluctuations, quite a bit of this outside air can actually replace the wine. This leads to the low fill level or ullage seen in older bottles.
Since high levels of oxygen, a highly reactive gas, is the single most damaging thing to wine, bottles that have undergone repeated temperature cycling tend to loose their freshness (at best) or spoil (at worst). For wine to age in a proper manner, temperature fluctuations must be minimized in both magnitude and frequency. Fluctuations of only 1.5ºC (3ºF) can be very damaging to wine if they occur on a daily basis.
