According to the 8:00 PM EDT intermediate advisory, the aircraft reconaissance flight currently in Hurricane Dean just reported a minimum central pressure of 920 millibars — down 10 mb from the last reading. Dean is strengthening again. The NHC isn’t reporting any change in the top wind speed yet, which may be because they’re waiting for additional recon data before making the call, or because it’s taking Dean’s winds a while to “catch up” with the falling pressure, or some combination of the two. Either way, I presume there will be a wind-speed bump in the 11:00 PM advisory, if not sooner in a special “update.” If it’s just a 5-mph bump, from 150 to 155, Dean will remain a Cat. 4. Otherwise, he’ll cross into Cat. 5 territory.

Is there a silver lining in this? Maybe. The deepening presumably means the eyewall replacement cycle is over. That’s a little sooner than I thought, and perhaps there will be time for Dean to start another cycle before landfall tomorrow afternoon. That could prevent the calamity of a landfall on the island as a strengthening Category 5 hurricane. But regardless, it ain’t going to be pretty in Jamaica tomorrow.

UPDATE/CORRECTION, 9:43 PM: On the other hand… if I’m reading the reconaissance report correctly, the aircraft is reporting a minimum central pressure of 918 millibars… but a maximum flight-level wind of just 123 knots! That’s 141 mph, which would normally translate to around 127 mph at the surface. Is Dean a 918-millibar Category 3?? I suppose I shouldn’t be so surprised — I remember some of the ‘05 hurricanes went through similar phases while their wind fields were expanding and their eyewalls were cycling.

Speaking of which: the aircraft reports that the strongest winds were in the “outer eyewall.” Apparently the eyewall replacement cycle isn’t over yet. So I guess you can forget my “silver lining” comment. But here’s a different silver lining: meteorologist and fellow weatherblogger Brian Neudorff comments that it “looks like there is some drier air getting into Dean. This seems to be consistent with what Accuweather’s Joe Bastardi was saying in his recent post. ‘Dean may weaken a bit the next 24 hours as dry air from the mountains of Hispaniola is drawn into the storm’.” If I’m not mistaken, hurricanes going through eyewall replacement cycles are especially vulnerable to disruption caused by dry-air entrainment. So that makes sense.

In any event, it will be very interesting to see what the NHC does at 11:00 PM. It appears we have ourselves a deepening, yet weakening, hurricane! Though to be honest, I wouldn’t be surprised if they hold the intensity at 150 mph, not wanting to downgrade it on the basis of a single recon report (which might have missed the strongest winds) only to upgrade it again in a few hours’ time.

UPDATE, 10:47 PM: The 11:00 PM advisory bumped the winds down only slightly, to 145 mph. Waiting for the discussion to post.

UPDATE, 11:06 PM: Here’s what the discussion says about Dean’s intensity:

THE INNER CORE OF DEAN APPEARS TO BE UNDERGOING SOME CHANGES. RADAR IMAGERY ONBOARD THE AIR FORCE RECONNAISSANCE AIRCRAFT DEPICTS CONCENTRIC EYEWALLS AT RADII OF ABOUT 10 AND 20 N MI…WITH THE OUTER EYEWALL RECENTLY BECOMING A LITTLE BETTER DEFINED. FLIGHT-LEVEL WINDS HAVE ALSO REVEALED DOUBLE MAXIMA. WIND DATA AT FLIGHT LEVEL…FROM THE SFMR…AND FROM DROPSONDES DIRECTLY SUPPORT AN INTENSITY OF NO MORE THAN ABOUT 115 KT. THE CENTRAL PRESSURE…HOWEVER…HAS BEEN GRADUALLY DROPPING AND WAS MOST RECENTLY MEASURED AT 918 MB. ASSUMING THAT THE MAXIMUM WIND HAS NOT BEEN SAMPLED…THE ADVISORY INTENSITY IS SET TO 125 KT…BUT THIS COULD BE A BIT ON THE HIGH SIDE. THE AIRCRAFT WILL CONTINUE TO INVESTIGATE DEAN FOR A FEW MORE HOURS TO SEE IF THE WINDS COME BACK UP.

Later, it adds, “THE SHORT-TERM INTENSITY FORECAST IS A BIT UNCERTAIN GIVEN THE DOUBLE EYEWALL STRUCTURE…BUT THE CENTRAL PRESSURE IS QUITE LOW AND THE INNER CORE COULD QUICKLY REORGANIZE AT ANY TIME…SO ANY DIP IN THE INTENSITY WILL PROBABLY BE SHORT-LIVED.”

More significantly, the track forecast keeps Dean just offshore of Jamaica. Hopefully that holds up.