000
WTNT44 KNHC 211435
TCDAT4
 
TROPICAL STORM NADINE DISCUSSION NUMBER  41
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
1100 AM AST FRI SEP 21 2012
 
NADINE REMAINS A MARGINAL TROPICAL CYCLONE. MODEL ANALYSES AND PHASE
SPACE DIAGRAMS SUGGEST THAT THE CYCLONE REMAINS WARM CORE...WHILE
SURFACE DATA AND SATELLITE IMAGERY INDICATE THAT THE CENTER OF
NADINE IS SOUTH OF THE FRONTAL BOUNDARY DRAPED ACROSS THE AZORES.
HOWEVER...THE CONVECTIVE PATTERN HAS DEGRADED SIGNIFICANTLY OVER
THE PAST FEW HOURS...WITH ONLY A RAGGED BAND OF WARMING CLOUD
TOPS REMAINING SOUTH AND EAST OF THE CENTER. THE DECREASE IN
CONVECTION IS LIKELY DUE TO A COMBINATION OF MARGINAL SSTS AND DRY
AIR THAT HAS WORKED ITS WAY INTO THE INNER PART OF THE CIRCULATION.
A 1224 UTC ASCAT PASS SHOWED SOME 40 TO 45 KT WINDS NORTHWEST OF
THE CENTER...AND THE INITIAL INTENSITY IS CONSERVATIVELY LOWERED TO
50 KT FOR THIS ADVISORY. TRANSITION TO POST-TROPICAL STATUS IS
EXPECTED SOON...POSSIBLY BY LATER TODAY IF ORGANIZED DEEP CONVECTION
DOES NOT RETURN. AFTER TRANSITION...ONLY SLIGHT WEAKENING IS
FORECAST.
 
NADINE MOVED A LITTLE WEST OF DUE SOUTH EARLIER THIS MORNING...
LIKELY DUE TO THE DEEP-LAYER FLOW BETWEEN A MID-LEVEL RIDGE TO
THE NORTHWEST AND A MID/UPPER-LEVEL LOW TO THE NORTHEAST.
HOWEVER...NADINE HAS TURNED SOUTHWARD RECENTLY...AND THE INITIAL
MOTION ESTIMATE IS 180/09. AS THE UPPER LOW BEGINS TO LIFT OUT TO
THE EAST...NADINE SHOULD TURN SOUTHEASTWARD OVER THE NEXT 12 TO 24
HOURS. AFTERWARD NADINE WILL AGAIN BE CAUGHT IN WEAK STEERING
CURRENTS...AND THE OFFICIAL FORECAST SHOWS A SLOW EASTWARD TO
NORTHEASTWARD MOTION AT DAYS 2 THROUGH 5. THIS FOLLOWS THE GENERAL
TREND SEEN IN MOST OF THE GUIDANCE...BUT AT A MUCH SLOWER FORWARD
SPEED DUE TO THE LARGE SPREAD IN THE MODELS LATE IN THE PERIOD.
THIS UNCERTAINTY STEMS FROM LARGE RUN-TO-RUN AND MODEL-TO-MODEL
VARIABILITY IN THE DETAILS ABOUT HOW MUCH NADINE WILL INTERACT WITH
ANOTHER TROUGH DEEPENING OVER THE NORTHEASTERN ATLANTIC LATE IN THE
PERIOD. DUE TO THE RECENT SOUTHWARD JOG OF NADINE...THE OFFICIAL
FORECAST HAS BEEN SHIFTED ABOUT 60 TO 70 NAUTICAL MILES TO THE WEST
AND SOUTH OF THE PREVIOUS ONE.

THE 34-KT WIND RADII WERE EXPANDED IN THE WESTERN SEMICIRCLE BASED
ON THE ABOVE-MENTIONED ASCAT PASS. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 34.1N  27.5W   50 KT  60 MPH
 12H  22/0000Z 32.9N  26.9W   50 KT  60 MPH
 24H  22/1200Z 31.8N  25.8W   50 KT  60 MPH...POST-TROPICAL
 36H  23/0000Z 31.4N  25.1W   50 KT  60 MPH...POST-TROPICAL
 48H  23/1200Z 31.4N  24.4W   50 KT  60 MPH...POST-TROPICAL
 72H  24/1200Z 31.6N  24.0W   45 KT  50 MPH...POST-TROPICAL
 96H  25/1200Z 32.0N  23.5W   45 KT  50 MPH...POST-TROPICAL
120H  26/1200Z 32.5N  22.5W   45 KT  50 MPH...POST-TROPICAL
 
$$
FORECASTER BRENNAN