The interaction with the trough to the north is really what sealed the deal for the sub-900 mb intensification as well, it seems. Melissa was floating in the ~905 mb range before that. Took an already pristine environment for the hurricane and just improved upon it even more, kinda similar to how you have the outflow boundary further modify and improve the kinematics of an already extreme environment on 4/27/11. Furthermore, you also had the fact this storm just never went through a full traditional EWRC. Just an absolutely absurd chaining together of pristine ingredients to lead to a complete behemoth of a hurricane.