Something is wrong and he moves up his departure, leaving Uncle to handle any emergencies.
Her vague letters have finally trickled off to nothing and he can't dismiss the awful feeling in his heart that something bad has happened.
He's written her faithfully—even more so now despite the overwhelming silence on her end and as the ship finally departs, he chafes at the slowness of their journey.
The air's coolness signifies that they're finally getting closer and he spends most of his time at the bow, watching the distance between them disappear as the ship cuts through the ocean.