Some reasoning from the most recent NHC forecast discussion:

THERE IS CONSIDERABLE UNCERTAINTY NEAR THE END OF THE
FORECAST PERIOD...WITH THE ECMWF AND UKMET MODELS SHOWING A
SHORT-WAVE TROUGH COMING OUT OF THE ROCKIES THAT INDUCES A RIGHT
TURN ON DAY 4. THE GFS AND NOGAPS HAVE A DIFFERENT PATTERN...WITH
MORE RIDGING EXTENDING WESTWARD TO THE NORTH OF IKE THAT KEEPS THE
HURRICANE MOVING BASICALLY WESTWARD. THE ECMWF HAS DONE VERY WELL
WITH IKE THUS FAR...AND HAS RELATIVELY HIGH SKILL IN FORECASTING
THE LARGE SCALE PATTERNS AT THE LONGER RANGES. OUT OF RESPECT FOR
THIS MODEL THE OFFICIAL FORECAST IS SHIFTED SLIGHTLY SLOWER AND TO
THE RIGHT OF THE PREVIOUS FORECAST...AND IS PRETTY CLOSE TO THE
DYNAMICAL MODEL CONSENSUS. BEGINNING TOMORROW AT 12Z THE NOAA G-IV
JET AIRCRAFT WILL BE SAMPLING THE ENVIRONMENT OF IKE TO ASSIST IN
THE DETERMINATION OF WATCHES AND WARNINGS.