I'm not sure 1 mb pressure drop constitutes a sign that appreciable intensification is underway -- heck 1 mb may be within the margin of error (or 90% confidence interval) of the pressure observations. However, it
could be a sign that weakening has stopped, but we'll need another center fix or two to know for sure.
The latest surface wind speed analysis from HRD is available at
ftp://ftp.aoml.noaa.gov/hrd/pub/hwind/2011/AL092011/0826/1930/AL092011_0826_1930_contour02.png. From that analysis, there are no hurricane force winds in the southwest quadrant of the storm. The winds in the northwest quad peak just above Cat 1 threshold, and the winds in the NE and SE quadrants are a little more solid Cat 1. Note that the analysis shows a peak wind of
77 kts to the east of the center; there are no Cat 2 winds in that analysis (based on Doppler radar aboard aircraft recon as well as in-situ and dropsonde observations).
A rather lengthy arc of dry air is seen entraining into the core of Irene on satellite imagery from this afternoon, indicating that Irene has wrapped up some drier air that lies to its southwest through north. Sfc obs don't reveal this dry air, but tropopspheric soundings from some locations in the southeastern U.S. reveal very dry mid-levels. For example, the GSO and RNK soundings sampled <10% relative humidity (RH) in the 550-300 mb layer several hours ago (1800 UTC). KFFC (Atlanta area) was a little more moist, but still showed RH <30% in the middle of the troposphere. Measured precipitable water (PW) at FFC and RNK were <1.40". Current UW CIMSS wind shear analysis continues to show 10-20 kts of deep-tropospheric shear over most of Irene. The combination of moderate vertical wind shear, dry air, and a rather messy inner core does not suggest that appreciable intensification is likely. That doesn't mean it's not possible -- it's just not likely. Thus, the NHC has toned down the forecast max wind speeds.
I'll reiterate that this should NOT mean that you should let your guard down. Do NOT let your guard down. If the local authorities tell you to evacuate, you should follow their orders. There is still the possibility that Irene could pulse back up in intensity tonight, and it could get back into a more solid Cat 2 range before the NC landfall or close call. This doesn't seem very likely considering how disorganized Irene currently is (particularly its inner core) and how very spread out Irene's wind field is. Continue to plan for appreciable flooding potential, and be careful out and about in case trees fall victim to the winds and wet soils!