[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 232043
TCDAT5

TROPICAL STORM JOYCE DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102012
500 PM AST THU AUG 23 2012

SATELLITE DATA INDICATE THAT THE CENTER OF JOYCE HAS UNEXPECTEDLY
BECOME EXPOSED. THE DEEP CONVECTION...WHICH WAS EARLIER THOUGHT TO
BE PARTIALLY COVERING THE CENTER...HAS BEEN CARRIED FAR TO THE
NORTHWEST ALONG WITH A STRONG MID-LEVEL CYCLONIC CIRCULATION...
LEAVING THE LOW-LEVEL CENTER BEHIND. AN 1816 UTC SSMI OVERPASS
CONFIRMED THIS STARK DECOUPLING...WHICH APPEARS TO HAVE RESULTED
FROM A COMBINATION OF SOUTH-SOUTHEASTERLY SHEAR AND DRY AIR.
ALTHOUGH DVORAK T-NUMBERS HAVE DECREASED AS A RESULT OF THE
DECREASE IN ORGANIZATION...IT IS ASSUMED THAT TROPICAL-STORM-FORCE
WINDS ARE STILL OCCURRING IN THE CONVECTION WELL TO THE NORTH IN
ASSOCIATION WITH THE MID-LEVEL CYCLONIC CIRCULATION.  THE WIND RADII
HAVE TEMPORARILY BEEN ADJUSTED TO REFLECT THIS DISPLACEMENT.

THE INITIAL MOTION ESTIMATE IS A HIGHLY UNCERTAIN 300/12 SINCE THE
CENTER POSITION WAS NOT WELL KNOWN EARLIER.  JOYCE IS EXPECTED TO
BE STEERED WEST-NORTHWESTWARD TO NORTHWESTWARD FOR THE NEXT FEW DAYS
AROUND THE SOUTH SIDE OF A SUBTROPICAL RIDGE OVER THE CENTRAL
ATLANTIC.  A TURN TOWARD THE NORTH AND THEN NORTHEAST SHOULD OCCUR
IN ABOUT 4-5 DAYS AS JOYCE ENCOUNTERS A BREAK IN THE RIDGE OVER THE
WESTERN ATLANTIC AND RECURVES INTO A STRONG BAND OF WESTERLIES TO
THE NORTH. THE NHC TRACK FORECAST HAS BEEN SHIFTED TO THE
RIGHT IN THE FIRST 48-72 HOURS TO ACCOUNT FOR THE POSSIBLE
REFORMATION OF JOYCE TO THE NORTH.  THE REMAINDER OF THE FORECAST
IS SIMILAR TO THE PREVIOUS ONE AND IS CLOSE TO A BLEND OF THE
ECMWF/GFS...WHICH SHOWED A DEEPER REPRESENTATION OF THE CYCLONE.

ONE OF TWO OPTIONS SEEMS PLAUSIBLE IN THE SHORT TERM WITH REGARD TO
THE INTENSITY FORECAST. A NEW LOW-LEVEL CENTER COULD FORM IN
ASSOCIATION WITH THE MID-LEVEL CYCLONIC CENTER AND BECOME DOMINANT.
THE OTHER POSSIBILITY IS THAT NO NEW CENTER WILL FORM AND JOYCE
WILL DISSIPATE. ASSUMING THAT JOYCE SURVIVES DURING THE NEXT DAY OR
TWO...THE PROSPECT FOR INTENSIFICATION SEEMS UNLIKELY FOR THE NEXT
2-3 DAYS. THE CONTINUED PROXIMITY OF A MID- TO UPPER-LEVEL
TROUGH...COUPLED WITH THE EFFECTS OF DRY AIR...SHOULD INHIBIT ANY
SIGNIFICANT STRENGTHENING. LATER IN THE FORECAST PERIOD...GLOBAL
MODELS CONTINUE TO ADVERTISE SOME CHANCE OF JOYCE INTENSIFYING
AROUND THE TIME IT RECURVES. THE NEW NHC INTENSITY FORECAST HAS
BEEN REDUCED DURING THE FIRST COUPLE OF DAYS AND MODIFIED UPWARD ON
DAYS 4-5.


FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 15.9N  42.5W   35 KT  40 MPH
 12H  24/0600Z 17.1N  45.1W   35 KT  40 MPH
 24H  24/1800Z 18.5N  47.9W   35 KT  40 MPH
 36H  25/0600Z 20.0N  50.8W   35 KT  40 MPH
 48H  25/1800Z 22.1N  54.4W   35 KT  40 MPH
 72H  26/1800Z 26.3N  60.4W   45 KT  50 MPH
 96H  27/1800Z 30.8N  63.0W   50 KT  60 MPH
120H  28/1800Z 34.5N  60.4W   55 KT  65 MPH

$$
FORECASTER KIMBERLAIN



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