[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 310902
TCDAT2
HURRICANE EARL DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072010
500 AM AST TUE AUG 31 2010

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT EARLIER REPORTED
700 MB FLIGHT-LEVEL WINDS OF 124 KT...AND ESTIMATED SURFACE WINDS
OF 112 KT FROM THE SFMR.  THE PLANE ALSO REPORTED A CENTRAL
PRESSURE OF 931 MB.  BASED ON THIS...THE INITIAL INTENSITY IS SET
AT 115 KT.  SINCE THE PLANE LEFT...A TRMM OVERPASS AND DATA FROM
THE SAN JUAN WSR-88D RADAR INDICATE THAT EARL HAS STARTED AN
EYEWALL REPLACEMENT CYCLE.  ANOTHER HURRICANE HUNTER AIRCRAFT WILL
ARRIVE IN EARL NEAR 12Z TO DETERMINE IF IT HAS PEAKED IN INTENSITY
FOR NOW.

THE INITIAL MOTION IS A WOBBLY 295/11.  THERE IS LITTLE CHANGE TO
THE TRACK FORECAST PHILOSOPHY FROM THE PREVIOUS ADVISORY.  EARL
SHOULD MOVE GENERALLY NORTHWESTWARD FOR THE NEXT 48 HR OR SO ON THE
SOUTHWESTERN SIDE OF THE SUBTROPICAL RIDGE.  AFTER THAT...THE
HURRICANE SHOULD TURN NORTHWARD AROUND THE WESTERN END OF THE
RIDGE...FOLLOWED BY A TURN TO THE NORTH-NORTHEAST AND ACCELERATION
ON THE EAST SIDE OF A STRONG DEEP-LAYER TROUGH MOVING INTO THE
NORTHEASTERN UNITED STATES.  THE TRACK GUIDANCE IS TIGHTLY
CLUSTERED FOR THE FIRST 72 HR...WITH SOME SPREAD IN THE TRACK
DIRECTIONS BETWEEN THE LEFT-MOST HWRF AND THE RIGHT-MOST GFS
ENSEMBLE MEAN THEREAFTER.  THE NEW FORECAST TRACK IS AN UPDATE OF
THE PREVIOUS TRACK AND LIES JUST LEFT OF THE CENTER OF THE GUIDANCE
ENVELOPE.

THE INTENSITY FORECAST IS A LITTLE PROBLEMATIC.  THE GFDL AND GFDN
MODELS SUGGEST THAT EARL COULD STRENGTHEN DURING THE NEXT 24 HR OR
SO...AND THIS COULD OCCUR IF THE HURRICANE COMPLETES THE EYEWALL
REPLACEMENT QUICKLY ENOUGH.  ON THE OTHER HAND...EARL IS FORECAST
TO BE IN AN ENVIRONMENT OF MODERATE SOUTHWESTERLY VERTICAL WIND
SHEAR...AND WATER VAPOR IMAGERY SHOWS VERY DRY MID/UPPER-LEVEL AIR
APPROACHING THE HURRICANE FROM THE NORTH.  THESE FACTORS COULD
PREVENT ADDITIONAL STRENGTHENING.  THE INTENSITY FORECAST WILL
FOLLOW THE GFDL/GFDN SCENARIO WITH A LITTLE MORE STRENGTHENING
DURING THE NEXT 12-24 HR...BASED ON THE HURRICANE COMPLETING THE
EYEWALL REPLACEMENT AND THE DRY AIR NOT REACHING THE HURRICANE
CORE.  THE FORECAST TRACK TAKES EARL OVER COLDER SEA SURFACE
TEMPERATURES AND INTO INCREASING SHEAR AFTER 72 HR...WHICH SHOULD
CAUSE STEADY WEAKENING AND EVENTUAL EXTRATROPICAL TRANSITION.

INTERESTS FROM THE CAROLINAS NORTHWARD TO NEW ENGLAND SHOULD MONITOR
THE PROGRESS OF EARL.  THERE IS STILL CONSIDERABLE UNCERTAINTY AS
TO HOW CLOSE THE HURRICANE WILL COME TO THE U.S. EAST COAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL      31/0900Z 20.5N  66.7W   115 KT
 12HR VT     31/1800Z 21.4N  68.2W   120 KT
 24HR VT     01/0600Z 23.3N  70.3W   120 KT
 36HR VT     01/1800Z 25.5N  72.3W   120 KT
 48HR VT     02/0600Z 28.0N  73.8W   115 KT
 72HR VT     03/0600Z 33.5N  74.5W   105 KT
 96HR VT     04/0600Z 40.0N  69.5W    85 KT
120HR VT     05/0600Z 48.0N  60.5W    60 KT...POST-TROP/EXTRATROP

$$
FORECASTER BEVEN


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