[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 170847
TCDAT2
HURRICANE JULIA DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
500 AM AST FRI SEP 17 2010

UP UNTIL THE LAST HOUR...JULIA HAD EXHIBITED A SMALL BUT WELL-
DEFINED EYE WITH A SOLID EYEWALL. SUBJECTIVE DVORAK CLASSIFICATIONS
ARE 77 KT...WITH ADT VALUES USING AN EYE PATTERN SUPPORTING
ANYWHERE FROM 75-85 KT. GIVEN THAT THE EYE HAS BECOME OBSCURED...
THE INITIAL WINDS ARE ONLY INCREASED TO THE LOWER END OF THOSE
ESTIMATES...75 KT. THE HURRICANE IS IN A SMALL LOW SHEAR ENVIRONMENT
TO THE NORTH OF AN UPPER LOW. HOWEVER...JULIA IS ABOUT TO ENCOUNTER
AN UPPER-LEVEL JET...PART OF THE OUTFLOW FROM IGOR...WHICH SHOULD
INDUCE SIGNIFICANT SHEAR AND A FAIR AMOUNT OF WEAKENING. JULIA
SHOULD MOVE AWAY FROM THE MAIN JET CORE IN TWO TO THREE DAYS...
CAUSING THE SHEAR TO MODERATE SOMEWHAT...BUT SLOW WEAKENING IS
STILL EXPECTED.  BY THE END OF THE FORECAST PERIOD...VERY STRONG
SHEAR IS FORECAST TO OCCUR...WHICH SHOULD CAUSE RAPID DISSIPATION.
THE NEW NHC INTENSITY FORECAST IS CLOSE TO THE PREVIOUS ONE AND THE
SHIPS MODEL...BUT BELOW MOST OF THE REST OF THE GUIDANCE.

JULIA CONTINUES TO MOVE 290/21.  THE HURRICANE APPEARS TO BE
LEAVING THE INFLUENCE OF A MID- TO UPPER-LEVEL LOW TO THE SOUTHEAST
...AND BECOMING MOSTLY STEERED BY A RIDGE OVER THE EASTERN ATLANTIC
OCEAN.  JULIA SHOULD GRADUALLY GAIN LATITUDE AND EVENTUALLY TURN TO
THE NORTH AND NORTHEAST AROUND THE WESTERN PORTION OF THE RIDGE.
THE TRACK GUIDANCE CONTINUES TO SHIFT WESTWARD...PERHAPS DUE TO THE
FAST WEST-NORTHWESTWARD MOTION AND UNFORESEEN IMPACTS OF THE MID-
TO UPPER-LEVEL LOW.  THE NHC FORECAST IS SHIFTED WESTWARD AGAIN
...AND LIES BETWEEN THE GFS ENSEMBLE AND THE MULTI-MODEL CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INITIAL      17/0900Z 23.8N  45.1W    75 KT
 12HR VT     17/1800Z 25.0N  47.6W    65 KT
 24HR VT     18/0600Z 27.2N  50.2W    55 KT
 36HR VT     18/1800Z 29.7N  51.9W    50 KT
 48HR VT     19/0600Z 32.4N  52.4W    45 KT
 72HR VT     20/0600Z 36.0N  49.5W    40 KT
 96HR VT     21/0600Z 40.0N  44.5W    35 KT
120HR VT     22/0600Z...DISSIPATED

$$
FORECASTER BLAKE



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