As Tip noted in the post above. Large systems such as 91L take a bit more time to consolidate and or spin up.
91L covers a large area of the Atlantic Ocean at present. While it's being limited by Saharan Dust to the north and dry air to the west it is retaining it's size.

Current satellite imagery shows that 91L extends from 41W to 56W and from 6N to 18 N. This system's cloud cover could possibly encompass the whole Lesser Antilles Island Group from north to south, at some point in the next three days.
Note: the 31 July 0245Z water vapor image indicates there may be some dry air ingestion on the NW Quadrant of the system. That could put a huge dent in the system.As we saw yesterday with Tropical Storm Don.

Interests in the Lesser Antilles, Virgin Islands, Puerto Rico and westward should pay close attention to this system.

Recon is scheduled to Investigate the system on Sunday Afternoon.