000 WTNT41 KNHC 280850 TCDAT1 HURRICANE DANIELLE DISCUSSION NUMBER 28 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062010 500 AM AST SAT AUG 28 2010 DATA FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT DANIELLE HAS WEAKENED...LIKELY AS A RESULT OF AN EYEWALL REPLACEMENT CYCLE. THE AIRCRAFT FOUND CONCENTRIC EYEWALLS WITH RADII OF 20 AND 60 NM AROUND 0345 UTC...AND SUBSEQUENT SATELLITE IMAGERY SUGGESTS THAT THE INNER EYEWALL HAD CONTINUED TO ERODE. THE AIRCRAFT MEASURED A MAXIMUM FLIGHT LEVEL WIND OF 100 KT AND A CENTRAL PRESSURE OF 950 MB. BASED ON THIS...THE INITIAL INTENSITY IS DECREASED TO 95 KT FOR THIS ADVISORY. WHILE ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR THE NEXT DAY OR SO...DANIELLE WILL NOT LIKELY HAVE ENOUGH TIME TO RESTRENGTHEN SIGNIFICANTLY AFTER THE EYEWALL CYCLE COMPLETES. THE INTENSITY FORECAST SHOWS LITTLE CHANGE FOR THE NEXT 24 HOURS...AND A SLOW WEAKENING IS INDICATED BEYOND THAT TIME AS THE VERTICAL SHEAR INCREASES AND THE HURRICANE BEGINS TO MOVE OVER COOLER WATERS. LATE IN THE PERIOD...DANIELLE WILL LIKELY TRANSITION INTO A LARGE AND POWERFUL EXTRATROPICAL CYCLONE OVER THE NORTH ATLANTIC...AND ONLY SLOW WEAKENING IS INDICATED DURING THE TRANSITION PROCESS. THE AIRCRAFT FIXED THE CENTER A LITTLE TO THE LEFT OF PREVIOUS ESTIMATES...AND SHOWED THAT DANIELLE HAS SLOWED A LITTLE. THE INITIAL MOTION ESTIMATE NORTH-NORTHWEST OR 345/8. THE TRACK GUIDANCE IS TIGHTLY CLUSTERED OVER THE FIRST 24 TO 36 HOURS...AS DANIELLE WILL ACCELERATE TOWARD THE NORTH AND NORTHEAST AS IT INTERACTS WITH A LARGE MID- TO UPPER-LEVEL TROUGH MOVING OFFSHORE OF THE U.S. EAST COAST. BEYOND THAT TIME...DANIELLE WILL SLOW TEMPORARILY FROM 48 TO 72 HOURS AS THE FIRST UPPER-TROUGH LIFTS OUT...AND THEN ACCELERATE AGAIN TOWARD THE EAST-NORTHEAST AS ANOTHER TROUGH CAPTURES THE CYCLONE AND THEN PULLS IT SHARPLY NORTHWARD BY DAY 5. THE OFFICIAL FORECAST HAS BEEN ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ONE THROUGH 24 HOURS DUE TO THE MORE WESTERLY INITIAL POSITION OF THE CYCLONE. BEYOND THAT TIME...A MORE SIGNIFICANT ADJUSTMENT TO THE LEFT OF THE PREVIOUS TRACK WAS MADE TOWARD THE MODEL CONSENSUS THROUGH 48 HOURS...AND TOWARD A BLEND OF THE GFS AND ECMWF AT 72 HOURS AND BEYOND. FORECAST POSITIONS AND MAX WINDS INITIAL 28/0900Z 28.6N 61.0W 95 KT 12HR VT 28/1800Z 30.2N 60.6W 95 KT 24HR VT 29/0600Z 33.2N 58.6W 95 KT 36HR VT 29/1800Z 36.7N 56.1W 90 KT 48HR VT 30/0600Z 38.9N 54.3W 85 KT 72HR VT 31/0600Z 41.5N 47.0W 70 KT 96HR VT 01/0600Z 47.1N 32.4W 70 KT...POST-TROP/EXTRATROP 120HR VT 02/0600Z 54.5N 35.5W 60 KT...POST-TROP/EXTRATROP $$ FORECASTER BRENNAN