I agree with emsr2d2.
My guess is that it is a question.
So, "cool" means "not very cold / fairly cold".
You can say, "The morning air was cool (so we went for a walk in the park). / "It was a cold morning (so we decided not to go out)."
Or: At the seaside - "The water is cool. Do come here and sit next to me." / "The water is cold. I'd rather sit in the sun."
WW