After heavy rains a few years ago we did a few things.
Being 1st floor Jardines we make sure drain hole is clear even though there is a small tile lip which will hold back any small build up.
The front door does have a rubber seal that is adjustable so may be too high, open door, put sheet of newspaper underneath and adjust height using screw in hinged corner till you can't pull easily pull out paper.
What of a draft excluder?
There will always be a gap of some sort but not had any issues since.