if you have actually been following some of the Tropical Storm weather guys like Dr. Jeff Masters, you would KNOW that the storm has been weakening and that winds are at Cat-2 (105 MPH) and that the eye-wall has shown a tear and signs of weakness. The NHC has elected to keep Gustav at a Cat-3 strength with their 11AM advisory, because the satellite appearance still supports Cat-3, as opposed to the Hurricane Hunter's planes that show it at Cat-2.
There is also a decent amount of upper level winds that are creating 10-15 knots of shear over Gustav.
From Dr. Jeff Masters:
"By this evening, Gustav will be passing over a cold eddy. The heat content of the Gulf will decrease as Gustav approaches the coast. As seen in a simulation done yesterday using the GFDL model (Figure 2), the relatively shallow depth of warm water near the coast will allow Gustav to upwell large amounts of cold water from the depths. This will chill the surface waters down by up to 5°C (9°F), which should weaken Gustav's winds by about 15 mph.
This cooling effect does not occur for Gustav's path over the southern Gulf of Mexico, due to the great depth of warm waters there. Both the GFDL and HWRF models respond to the lower heat content waters near Louisiana by weakening Gustav to a Category 3 hurricane with 115-120 mph winds at landfall. These models are the only ones that incorporate detailed depictions of the thermal structure of the Gulf of Mexico into their runs."
http://www.wunderground.com/blog/JeffMasters/show.html
