Hay mucha humedad.
Ay MOO-chah oo-meh-DAD
There is a lot of humidity.
Simple
Está muy húmedo hoy, el aire se siente pesado.
Es-TAH MOO-ee OO-meh-doh oy, el AI-reh seh SYEN-teh peh-SAH-doh
It is very humid today, the air feels heavy.
pesado = heavy
Hay un bochorno insoportable, estoy sudando sin hacer nada.
Ay oon bo-CHOR-no in-so-por-TAH-bleh, es-TOY soo-DAN-doh seen ah-SER NAH-dah
There is unbearable muggy heat, I am sweating without doing anything.
bochorno = sultry/muggy heat, very specific Spanish word for this feeling
More Spanish Weather Phrases