Cómo describes las playas en puerto rico?
húmedas
húmedo
tranquilo
tranquilas
claros
claras

Húmedas, tranquilas y claras.

Explanation:

The noun "beach" in Spanish is translated as "playa". When you add the suffix -es to "beach" in English you get the plural noun "beaches".

In the case of Spanish when you add the suffix -s to the noun "playa" you get a plural noun "playas".  

As you can see adjectives do not need to be pluralized:

I would describe Puerto Rico's beaches as wet, quiet and clear.

However, in Spanish the noun must agree in number and gender with the noun:

Yo describiría las playas de Puerto Rico como húmedas, tranquilas y claras.