There will be some restaurants closed, yes. But there will still be many, many choices to choose from. Regarding rain, unless there is a tropical system, which there is no way of knowing that ahead of time, there will be occasional showers, but should be no total rainouts. It's a bit different being on land, versus being on a boat, but I personally love travelling to SXM in September and October, as there are no crowds anywhere, no need for reservations at restaurants, etc.