General synonyms:
* Moist
* Damp
* Muggy (especially for hot, humid weather)
* Heavy (air)
* Oppressive (atmosphere)
More specific synonyms:
* Dewy (for a surface covered in moisture)
* Soaked (for something completely saturated with moisture)
* Stifling (for air that is difficult to breathe due to humidity)
* Sweltering (for hot, humid weather)
* Claustrophobic (for a feeling of being trapped by humidity)
The best word to use will depend on the specific situation and the tone you want to convey.
