What's the weather like?
It's hot. / It's warm. / It's sunny. (When the weather is warm, I prefer light clothing like t-shirts.)
How's the weather?
It's rainy. / It's humid. (Rainy days are the best time to stay home and read a book.)
What's the weather like?
It's cloudy. (It looks cloudy; you should bring an umbrella in case it rains.)