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 201 
 WTNT42 KNHC 160903
 TCDAT2
 HURRICANE JULIA DISCUSSION NUMBER  17
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
 500 AM AST THU SEP 16 2010
  
 THE SATELLITE PRESENTATION OF JULIA HAS CONTINUED TO DETERIORATE
 OVER THE PAST FEW HOURS.  MOST OF THE DEEP CONVECTION IS DISPLACED
 NORTH OF THE ESTIMATED CENTER POSITION...AND CLOUD TOPS HAVE
 CONTINUED TO WARM.  JULIA IS CURRENTLY SITUATED OVER WATERS OF
 26-27C...AND THE MID- TO UPPER-LEVEL TROUGH/LOW BETWEEN JULIA AND
 HURRICANE IGOR IS IMPARTING 20 TO 30 KT OF SOUTHWESTERLY SHEAR OVER
 JULIA ACCORDING TO THE UW-CIMSS SHEAR ANALYSIS.  BASED ON A BLEND
 OF SUBJECTIVE AND OBJECTIVE DVORAK INTENSITY ESTIMATES THE INITIAL
 INTENSITY IS LOWERED TO 90 KT FOR THIS ADVISORY.  WHILE THE SHIPS
 MODEL OUTPUT SHOWS THE SHEAR DECREASING TO LESS THAN 20 KT FROM 12
 TO 24 HOURS...JULIA WILL REMAIN OVER MARGINAL SSTS THROUGH THAT
 TIME.  THEN BY 36 HOURS OR SO...WHEN JULIA TEMPORARILY MOVES BACK
 OVER WARMER WATERS...THE SHEAR INCREASES TO AROUND 30 KT AND
 REMAINS HIGH FOR THE REST OF THE PERIOD.  THIS SCENARIO SHOULD
 RESULT IN A GRADUAL WEAKENING FOR THE FIRST 48 HOURS...WITH MORE
 RAPID WEAKENING TOWARD THE END OF THE PERIOD.  THE OFFICIAL FORECAST
 REFLECT THIS AND FOLLOWS A BLEND OF THE LGEM AND SHIPS MODELS
 THROUGH 48 HOURS...AND IS CLOSEST TO THE LGEM THEREAFTER. 
  
 WITH A LACK OF MICROWAVE IMAGERY OVER THE PAST FEW HOURS...THE
 INITIAL MOTION ESTIMATE OF 310/16 IS BASED LARGELY ON CONTINUITY
 AND THE ASSUMPTION THAT THE LOW-LEVEL CENTER REMAINS DISPLACED SOUTH
 AND EAST OF THE DEEP CONVECTION.  THE TRACK FORECAST REASONING
 REMAINS UNCHANGED FROM THE PREVIOUS PACKAGE.  JULIA IS CURRENTLY
 BEING STEERED NORTHWESTWARD BY THE UPPER-LEVEL LOW TO ITS SOUTHWEST
 AND A LARGE MID-LEVEL RIDGE TO ITS EAST...AND THIS WILL CONTINUE
 FOR THE NEXT DAY OR SO. THEN...AS JULIA MOVES AWAY FROM THE
 UPPER-LOW...THE CYCLONE WILL MOVE AROUND THE WESTERN PERIPHERY OF
 THE RIDGE AND TURN EAST-NORTHEASTWARD BY THE END OF THE PERIOD AS
 IT COMES UNDER THE INFLUENCE OF THE MID-LATITUDE WESTERLIES.  SOME
 DIFFERENCES REMAIN IN HOW SHARPLY JULIA MOVES AROUND THE RIDGE...
 WITH THE UKMET SHOWING A SHARPER TURN...WHILE THE ECMWF AND HWRF
 SHOW A WIDER TURN.  THE OFFICIAL FORECAST HAS BEEN ADJUSTED TOWARD
 THE TVCN MULTI-MODEL CONSENSUS...AND IS CLOSE TO THE GFS FOR
 THE FIRST 72 HOURS...WHICH REPRESENTS A COMPROMISE BETWEEN THE
 ECMWF AND UKMET. THE NEW NHC FORECAST IS ALSO FASTER THAN THE
 PREVIOUS PACKAGE DURING THE FIRST 24 HOURS...ACCOUNTING FOR THE
 OBSERVED ACCELERATION OF JULIA.   
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      16/0900Z 21.2N  36.2W    90 KT
  12HR VT     16/1800Z 22.8N  38.8W    85 KT
  24HR VT     17/0600Z 24.6N  42.4W    80 KT
  36HR VT     17/1800Z 26.4N  45.5W    75 KT
  48HR VT     18/0600Z 28.3N  47.7W    70 KT
  72HR VT     19/0600Z 32.5N  49.5W    65 KT
  96HR VT     20/0600Z 35.0N  46.5W    50 KT
 120HR VT     21/0600Z 36.0N  42.5W    40 KT
  
 $$
 FORECASTER BRENNAN
  
 
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