Going out on a limb tonight with the mention of dry air, shear, and hostile environment for further development. Looking at the diagnosis tools from CIMSS Cooperative Institute for Meteorological Satellite Studies Space Science and Engineering Center / University of Wisconsin-Madison, I think as plenty of others do in the tropical community, that the re-positioning of the storm center is due to the sheariing environment around the storm. From the shear tendency tools we find that the shear over the past 12 hours around the storm has doubled. As to click on the link you'll see the current graphic, click on the -3hr tab in the menu to see previous versions.
There is clearly a large influx of dry air surrounding Issac tonight indicated by the MIMIC TPW (Morphed Integrated Microwave Imagery...Total Precipitable Water) products.Many people much smarter than I have been talking about the dry environment around the storm and the potential impact to development.
As mentioned above the latest flight into Issac has found the center is further south and the tracks will obviously be adjusted in the 5 am update so will not even try to interpolate this at this time. Take a look at the National Hurricane Center site for the updated track and probabilities in the morning.
Many people are talking about data and the forecast in a negative way. The maximum wind speed probabilities obviously are taking the data into account as they are not very robust with the intensity forecast for the storm.
The highest hurricane probability is 38% for a category one storm in the 36 hour period. The reason for the forecast and track of Issac is the model output. With such good agreement this has to be taken into account as well. The spread in the track forecast is non-existent with the ECMWF as the only outlying model in the group.
The ECMWF has been right of all the other for several days, but also has a robust system moving up the eastern Gulf of Mexico. With that being said the forecast takes all this information in. The official forecast is reasonable and responsible. The upper level winds near and around the storm are shown in the following graphic.
The next 24 hours should reveal the true nature of Issac and produce a better forecast solution. The latest CHGHUR message from NHC still has chance for a 100 knot storm in 96 hours.
So we wait a little longer for more data and the storm to either get its act together or not.
For the latest information for official impacts and forecasts please visit your local National Weather Service Office website, or the National Hurricane Center website. Please remember that the center line of the forecast has an error. I saw some news stories today the showed the line only, which is a disservice to you. Remember Charley and the cone, the entire west coast of Florida was in the forecast cone and media didn't pay attention to what the hurricane center was putting in the forecast, they just went with what made the highest impact. It is easy to remember...use (.gov) not (.com). Your tax dollars at work. :-)