It's a common way to comment on the hot weather. You can use it as a greeting or as a conversational starter in situations where the heat is noticeable.
Here are some examples of how you could use it:
* "Que tal de calor? ¡Hace un calor terrible!" (How about the heat? It's unbearably hot!)
* "Hola, ¿que tal de calor?" (Hello, how about the heat?)
* "Uf, que tal de calor, ¿no?" (Whew, how about the heat, huh?)
Keep in mind that the tone of the phrase can vary depending on the context. It can be a simple comment on the weather or a more emphatic way to express how hot it is.