We used to go to SXM in September or October fairly regularly. We always travel off season and September is the HEIGHT of off season. On the French side, a lot of restaurants will be closed, but there still will be plenty of places to eat. On the Dutch side, some places will be closed, but not nearly as many as on the French side. There is NO traffic anywhere. No need for restaurant reservations. Often you can get cheap airfare for then. Do make sure that you purchase travel insurance. Look at the coverages and make sure there is coverage for storms.
For US, now that we live in Florida, I worry more about getting hit HERE than THERE, so I probably wouldn't go in September now unless it was a really special occasion. For you, if you don't have any such problems, I say go for it!!
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