Karl will be way too far to the east when it recurves and goes extratropical to have an impact on Jeanne. Maybe it'll pump up one of the ridges in the Atlantic, but more likely the one near Africa/Europe than anything.

Extratropical transition of tropical cyclones is a process that is only partially understood now. There are many identifying signs: the cloud pattern becomes asymmetric and more representative of a midlatitude system, the SW portion of the eye begins to collapse, the wind field expands away from the center, and the center of the storm transitions from a warm core to cold core (at the surface & aloft) -- among other things. The exact timeline and path that these transitions storms undergo is still under research as well as identifying characteristics that can help better forecast the transition and impacts of transitioning storms along the coastline.