"This is summer season."
Translation:यह गर्मी का मौसम है।
If you feel you must use "season" for "मौसम," then you would say "This is the summer season." Or, "This is the season of summer." Even though "मौसम" is there in the Hindi, however, more natural translations would be either "It's summer," or "It's summertime." (Even using "this" in the English—again, a literal translation of the "यह"—makes it sound overly emphatic, as if, after a long winter and not-so-great spring, someone woke up one morning to a lovely summer day and thought, "This is summer!")