ah, the Fuiji-wahra effect. (spelling is probably way off)

I remember some years ago it happened in the Pacific, as one storm tried to rotate around the other. In the Atlantic, I remember Isis being destroyed by the outflow of a close upstream system.
There was another instance in the last 10 years I think there were actually 5 classified systems in the Atlantic at the same time, but all were well-spaced.
As crazy as this year has been, the unusual is becoming the usual.

One note on post-landfall: I hope the forecast of this system stalling does not verify because it will turn into a situation like Allison. Wherever that sits, with the upslope flow, this can be devastating to many areas, in all different ways. The latest GFS does move it a little more, but still keeps it stuck.