Llueve.
YWE-veh
It rains.
Single verb, simplest
Está lloviendo bastante fuerte.
Es-TAH yo-VYEN-doh bas-TAN-teh FWER-teh
It is raining quite hard.
bastante = quite/enough, natural intensifier
¡Está lloviendo a cántaros, mejor quedarse en casa!
Es-TAH yo-VYEN-doh ah KAN-ta-ros, meh-HOR keh-DAR-seh en KAH-sah
It's raining pitchers, better to stay home!
a cántaros = in pitchers, classic Spanish idiom for heavy rain
More Spanish Weather Phrases