help hornets wasps
You have had European hornets find their way into your basement. This is wasp that often builds their nest in hollow trees or in areas with cavities. They sometimes will build nests in wall voids, attics, or areas with cavities that are seldom disturbed. Nests found in wall voids may have a slight odor associated with them (from what I have read).
This wasp can fly at night and will fly towards light. If lights were on in the basement they may have flown towards that and found their way inside one of the evenings you were away. We were experiencing drought conditions prior to the hurricane and the wasps could have been looking for sources of moisture. They could have found their way in while searching for moisture while you were on vacation.
The wasp has obviously found a way to get into your basement and I suspect there is a gap or access point they found. There could be gaps along windows, underneath a door, or an access from a void in a wall that reaches the outside of the home. This wasp does not use the same nest from year to year; however if there is sufficient space available they could build a nest in the gap as space allowed. You may wish to observe the basement area for wasp activity to see if you can see where they are coming into the home. Since you haven't found them coming into the home the entire summer (which is what I would have suspected if it was in the wall), I think they may have only now found an access point. Another possibility is the wasps found in your basement are males and females that are searching out areas (typically occurs in mid-July or so) for overwintering and next year. This would suggest you could possibly have a nest in a wall void or in the attic and they made their way into the basement during their search.
You may want to contact a local professional applicator to inspect the home for possible areas the wasps might be able to use. Professional pest control operator will be aware of management options, insecticides and practices available if a nest is found. I am unable to recommend any specific pest control business.