Convection increased on August 11 , and by August 12 the contact between a tropical wave and an upper-level low in the area resulted in a large area of disorganized thunderstorms extending from the western Caribbean Sea into the central Bahamas . Convection increased on August 11 , and by August 12 the interaction between a tropical wave and an upper-level low in the area resulted in a large area of disorganized thunderstorms extending from the western Caribbean Sea into the central Bahamas .