Yes, yes, yes......it's sunny just now but our experience tells us that the best cure is prevention and to that end we think you should look at those little jobs that need carried out to any external doors before we get the kind of weather shown in the pictures below.
I was genuinely glad I had both my timber doors (front and rear) all fitted with the best quality weather bars and draught strips, the weather bar is the aluminium (or gold colour) trim which is fixed by screws drilled in to the door step and a corresponding "drip" fitted to the bottom edge of the door, weather bars are available in numerous styles and normally as mentioned above in aluminium or gold colour aluminium.
You will need an electric drill with masonry drill bit, rawl plugs, some mastic to seal the bottom section of weather bar to the step, Philips type star screwdriver and a hacksaw....oh! and a measuring tape.
The weather strips which surround the door are made in the same materials/colours as the weather bars and are fitted to the two long edges of the door frame and also at the lintol (the top) of the door, they have a soft neoprene gasket which compresses tight to the door when the door is closed, don't be fooled in to buying the type of weather strip that has a larger black rubber seal, although it is larger it does not seal anything like as well as the one I have linked to above.
You will need a hammer (if the strip is fitted with pins) a Philips type star screw driver and a hacksaw, always fit the lintol section first, then fit the legs up to the lintol, it is always best to crimp/squash both ends of the weather strip legs as this will prevent the rubber gasket creeping and thereby leaving a gap.
The image above is Arthurs Seat in Edinburgh, this mountain in the distance is actually an extinct volcano and it's in the centre of the city.