When the weather is hotter outside then the engine in a car will usually run a bit hotter in the summer than it would in the winter.
However the hot weather shouldn't cause a significant increase in the engines operating temperature and if it is running too hot or overheating in the summer then something is wrong.
My vehicles run around 10 F higher in temperature during the summer months and tend to run a bit cooler in the winter months.
Also having the air conditioner on puts more strain on your engine as well which can increase the operating temperatures of your vehicle.
Your engine should run between 195 F to 220 F engine temperature and if it gets any higher than that it can begin overheating which can lead to warped engine heads and other engine damage.
But if you're just say 10 or 20 F above that 220 F then your engine is likely okay especially if the weather outside is hot.