December more likely for Fed lift-off than October

The key factor that held the Fed back is China, or specifically the possibility of a more abrupt slowdown in China which could then spill over to the global economy and financial markets. The Fed wants to see this question "revolved to some extent" before it raises rates. 

"One rate increase this year is expected, however the outlook for a September hike has failed to materialize and now it has to be decided which meeting is more likely. The odds favor the December gathering rather than October", says Societe Generale. 

Unfortunately, it is unlikely to be resolved over the next eight weeks which makes an October rate hike unlikely. Moreover, the potential split within the FOMC core also raises the hurdle for the October meeting. 

Yellen will want this individual in the consensus and this will probably require a good string of positive data. Another potential issue facing the Fed is the small, but non-negligible risk of a government shutdown and another debt ceiling showdown.