About 5%, see here

not 100% sure on if the special sounding data will make it for the 0z runs, but it's likely. I'll try to find out, by 6 or 12Z for sure though. Some of the 18Zs coming out may have partial data from it. The data it's collecting (along with the other special soundings) is extremely important with this environmental setup in determining the future track of Irene. There is the NOAA jet, and an airforce plane also doing upper air soundings up right now over the area north and west of Irene. The NHC is taking them very seriously.

Irene's center (Aka central dense overcast) is very symmetrical right now, and the best it's ever looked. South side of the storm is still rugged looking though and probably will remain so until it gets away from Hispaniola. North side is looking very good, although some elongation west to east.