From the Nassau Yacht Harbor (the article was written in July, proclaiming the jellyfish were back.)
“Generally found in Bahamian waters from spring through the early summer, in various stages, they can make swimming and enjoying the waters quite uncomfortable.”
It‘s when the water is warming up from Winter.
They are called Thimbles, and seem to cause problems when trapped in your clothes - more than the ones in the Gulf when you touch/ step in one.