Your analysis is spot on regarding heavy rainfall potential for southf Florida. If 90-L develops some more east of the Cape, then retrogrades WSW/SW across the Space/Treasure coast as forecast, the NE surge kicking in Saturday along the coast north of the Cape associated with the frontal trough and low will drive the bulk of moisture across the south half of Florida.

Drier air entrained into the circulation from the NW will lead to considerably lower rain chance for the north half of Florida, and the heaviest showers/storms will congregate just inland along and to the south of the I-4 corridor, then drop SW away from my still-thirsty central coastal Volusia rain gauge (2"+ July deficit, 6" annual deficit to date).