Hermetic Seal
According to Junior Energy, fluorescent bulbs use a hermetic seal, which means no humidity will penetrate the bulb itself. This seal is necessary to keep the toxic mercury vapor from leaking out into the environment.
Corrosion
Humidity can cause corrosion of the metal fixtures on the ends of a fluorescent bulb, impeding its ability to transmit electricity. The corrosion is easily avoidable by purchasing a weatherproof fluorescent bulb, as they are resistant to corrosion.
Condensation
Excess buildup of condensation on the outside of the bulb can cause it to take longer to turn on, write Coaton and Marsden. The temperature difference on the glass negatively affects the delicate process within. Wiping the condensation off the bulb and waiting for five minutes will remedy the problem in most situations. Additionally, purchasing a weatherproof fluorescent bulb will avoid the problem altogether.