Interesting that Avila mentions that he is hesitant to forecast a stronger system because the GFDL does not develop it at all. The GFDL did not develop Katrina into a tropical storm until after it became a tropical storm, at which point it suddenly started forecasting a major hurricane. Given the uncertainties involved, I think the official forecast is very reasonable. If it can consolidate soon and sit over the Gulf Stream for awhile, it could become a hurricane, but if it moves quicker than expected toward the coast or the shear does not diminsh as expected, it may not even become a tropical storm. The 10% wind speed probabilities on the 5pm advisory are at 110 mph (borderline cat 2/3) at the high end and 25 mph (generally considered below T.D. status) on the low end at 72 hours, which is a good indication of the uncertainty in this particular case.