It’s inevitable. The day after the US Open ends, the clarity and narratives that propelled tennis through most of the summer vanish.It doesn’t help that the tours ramble off to relatively new outposts in Asia and Russia before wending their way back, at least in the case of the ATP, to a more traditional finale in Europe and London. Another stumbling block to clarity: Both tour calendars are crowded with tournaments, many competing directly with each other.Don’t be fooled. Let’s make some sense of what the tours have in store for us in the coming weeks.What’s at stake?Top-ranked Novak Djokovic has a massive lead of nearly 5,000 ranking points over No. 2 Andy Murray. That’s the equivalent of a Grand Slam win and victories in three Masters 1000 events. Murray’s lead over No. 3 Stan Wawrinka is also significant — more than 3,000 points. With Roger Federer out for the year and Rafael Nadal at a distant No. 4 but still a shadow of his former combative self, there will be no musical chairs at the top level. From Nadal on down, though, almost everyone is either vulnerable or facing a significant opportunity.That opportunity would culminate with the year-end championships in London. The top eight players in the world qualify, and with Federer out, it opens the door for someone else. Right now Nadal sits in the eighth position in the race (not to be confused with the rankings). Tomas Berdych and Marin Cilic are close behind; a strong finish could propel them into the season’s final event.