Some fireplace doesn't have a chimney on the roof.
Instead, it has a wall mounted vent like this one below.
Problem
When there is heavy storm with gusty wind, the water will come in this vent and flowing the fireplace.
What's the solution?
A temporary solution is to cover this FirePlace vent with a garbage bag? => Travis put a piece of metal to cover the fireplace vent.
Later, Pedro found some leaks on the roof. So the fireplace vent may not be the root cause after all.
In addition, it was wrong to use rubber washers for the screws showed below since it's not heat resistant. Pedro removed these screws and restore the fireplace vent.
The real fix is as follows:
Finally, rotten plywood was replaced, the roof tiles were replaced, the gutters were cleaned up.