SST's show a large region of warmer than normal temperature anomalies in the waters surrounding Greenland and as far south as Nova Scotia, Canada. This large warm water anomaly gives a strong indication that a negative NAO is present in the area, with no signal that it is to let up soon.
I feel that the ensemble forecasts are not in the most accurate of realms- yesterday they were displaying a trend to a positive NAO phase, whereas today the ensembles have shifted to a more negative phase. That said, I don't have too much confidence in the ensembles at this time, but I do believe that the forecast listed above is more likely to pan out than a positive NAO.
Because the stratosphere remains at near normal levels rather than cooler than normal, I believe that the negative NAO will remain in place for a while to come.
Is it possible for the negative NAO to stick around into winter? It's possible, but prolonged patterns are like trying to treat diseases with one type of medicine- the more you use that one type, the more potential the disease has to find a way around it and break down the medicine's effectiveness. In this case, the atmosphere could find a way to break through the negative NAO and intense high pressure regimes before winter. Accurate forecasting on those regimes, however, is not warranted at this time.