It's cool
시원하다
It's cooler
더 시원하다
It's cooler than yesterday
어제보다 시원하다
It's much cooler than yesterday
어제보다 훨씬 더 시원하다
It's getting cooler
더 시원해지고 있다
It's getting much cooler
훨씬 더 시원해지고 있다
It has gotten cooler
시원해졌다
It gotten much cooler
훨씬 더 시원해졌다
It's gotten (much) cooler
It's definitely gotten (much) cooler
확실히 더 시원해졌어