Guess it had something to do with being in closer proximity to a Borg ship (and its vinculum, if you REALLY want to believe that sort of thing exists) allowing him to pick up on various drones' status reports to the hive mind. I think the novelization has prose to the effect of Picard hearing voices saying there was significant damage in a particular place which would allow a fatal, cascading explosion if hit. Or something.
In any case, he had to get close enough to go from spooky flashback dreams to actual contact. This continued through the rest of the movie as he was able to hear snippets of what the queen was up to in the basement.