The black and orange depict how dry the air is, and this "batch" came down with the trough that pulled Ivan NW and NNW. Even though the trough is departing, the dry air is actually being drawn into the very large circulation of Ivan. Whenever a tropical system ingests dry air, it has a chance to weaken because the hurricane needs a very warm, moist, environment as the energy to keep convection going. Sometimes it is temporary, and in this case, the NHC is expecting the atmosphere to be a little less hostile towards Ivan in about 24 hours I think.
I would also point out that this storm is very lopsided, as per Dr. Neese's explanation on TWC. This is also a direct result of the westerlies impacting Ivan, and again, Ivan was pulled up into these westerlies by that trough that left the dry air in the Gulf. It is almost as if the atmosphere is trying to "shove" the storm to the right, but it still remains a bully of a system.