Last year (my first year) I worried when I saw that that the bees were about to swarm. A lot of helpful people on this list told me that it has to do with the temperature and hive ventilation. Following their advice, I did the following things:
1. Made sure I had an open screened bottom board on each hive
2. Propped the top to make a top entrance by placing a stick to raise up the telescoping cover (adds air circulation and gives them a top entrance)
3. Bought slatted racks for all of my hives (allows the bees to hang out inside the hive rather than on the porch.
The bees on the porch may be out there because the hive is too warm and are there to use their wings to circulate air. They may also be there simply because their added body heat is making the hive too hot.
Even with the SBB, slatted rack and top propped in the hottest nights in Hotlanta, they still hang out on the porch but the beard is much smaller than without proper ventilation.
Hope that helps,
Linda T in Atlanta (with thanks to Brian Bray, Michael Bush, and others who helped me on this issue last year)