It could be, but it's more likely temporary fluctuations inside the core of the storm. It's a rather dry environment that the storm is embedded in and it appears a temporary lull in the wind shear around the storm may be coming to an end. While the Gulf Stream has some of the warmest, deepest waters in the basin, they can't support a storm forever. It'll be tough to make a call on the storm now as to whether upwelling is playing a role, but much longer in the same area -- or a trip away and then back -- and it'd be a much easier distinction to make. For now though, the storm doesn't look quite as impressive as it did earlier today.

It looks to be more of a breakdown of the eyewall as opposed to concentric eyewalls. It's not uncommon for hurricanes of all intensities to undergo eyewall replacement cycles; you just see it more often with intense storms as they are able to maintain their eyewalls for longer periods of time than weaker storms are (which often go through phases of trying to define a better eyewall as opposed to true replacement cycles) able to do so.