I posted this very same question about 6 months ago when I first discovered Cruise @ddicts. I received quite a few responses, most of which encouraged me to take advantage of the lower rates in September regardless of the "Hurricane Season." I was told that *usually* the worst case scenario would involve a change in ports of call, as the captain will do everything possible to steer clear of any storms. So you may skip a port of call, or you may have your itinerary "swapped" - for example, you may be re-routed through the Western Caribbean instead of the Eastern Caribbean. From the responses I read, I felt confident enough to book a cruise on the Explorer for 9/21/02. The most important thing for me is that I will NOT be at work - so if I end up in Cozumel instead of San Juan, so be it!
Good Luck!