Warm wet air is condensing inside an uninsulated duct in a hot attic and running back down into the fan housing. It is condensation from your own shower, not a roof leak, and it means the duct is either uninsulated, sagging, or not vented outside at all.
Confirm it is condensation
Condensation drips during or shortly after a shower and stops in between. A roof leak drips during or after rain and does not care whether you have showered. If you cannot tell, run the shower hot for fifteen minutes on a dry day and watch the fan.
What is happening above your ceiling
A Florida attic in summer is brutally hot, but the duct carrying air out of your bathroom is full of moisture-saturated air. Where that duct passes through the attic, the moisture condenses on the inside of the duct wall. With nowhere else to go, it runs back down the duct — downhill, into your fan housing, and out through the grille.
The three faults, and they usually come together
No insulation on the duct
Bare flex duct condenses. Insulated flex duct mostly does not. This is the single most common cause and the cheapest to fix.
A sagging run
Flex duct draped between joists forms low spots, and low spots collect the condensate into a pool that eventually backs up into the fan. The duct should run as short and as straight as possible and slope away from the fan, so anything that does condense drains toward the outside vent rather than back at you.
It does not actually go outside
Worth checking every time. A fan discharging into the attic dumps every shower's worth of moisture onto your roof deck and insulation. The drip from the fan is then the least of the problem — you get damp insulation, mould on the underside of the sheathing, and in bad cases rot. It must terminate at a roof cap or soffit vent with a working backdraft damper.
What to check yourself
- Is the duct insulated along its whole length?
- Does it sag anywhere between the fan and the vent?
- Does it actually reach an exterior vent, and is the damper free to open?
- Is the insulation around the fan housing damp or compacted?
When to stop and get someone up there
Stained or sagging drywall around the fan, damp insulation over an area rather than a spot, or any dark staining on the underside of the roof sheathing. At that point the moisture has been going somewhere for a while and the fan is the symptom rather than the fault.