It's an interesting idea wrt upwelling; I did consider this but ... Danielle was one system so far in an oceanic arena that has positive anomalies in oceanic heat content over a large area - I've been toying with the idea that the SSTs are not perturbed enough by Danielle. High resolution infrared of the SSTs may shed some light, though I haven't had the time.

What I did notice though is that Danielle weakened for a stint when also passing near these same longitudes, which was also similar in spatial-temporal positioning to when Earl also encountered SAL per CIMSS. That specific commonality is what led me to thinking along the lines of more atmospheric dynamics.

Either way, I think Earl is headed toward being an impressive TC. Whether upwelling or SAL aside (probably both to some degree respectively) both factors would be escaped along this current trajectory placing Early in a region where neither would mitigate strengthening.