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 684 
 WTNT42 KNHC 150859
 TCDAT2
 HURRICANE JULIA DISCUSSION NUMBER  13
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
 500 AM AST WED SEP 15 2010
 
 A RAPID STRENGTHENING EPISODE WAS NOTED A FEW HOURS AGO.  THIS WAS
 MOSTLY UNEXPECTED...AND REMINDS US OF OUR LIMITED UNDERSTANDING OF
 TROPICAL CYCLONE INTENSITY CHANGE.  JULIA IS STILL STRENGTHENING...
 BUT AT A SIGNIFICANTLY SLOWER RATE THAN WAS OBSERVED LAST EVENING
 AND EARLIER THIS MORNING.  ALTHOUGH THE EYE HAS NOT WARMED
 MUCH...THE CONVECTIVE BANDING AROUND THE EYE HAS BECOME BETTER
 ORGANIZED.  SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 115
 KT...AND THAT WILL BE THE INITIAL WIND SPEED FOR THIS ADVISORY...
 MAKING JULIA A CATEGORY FOUR HURRICANE.  JULIA COULD STRENGTHEN A
 LITTLE MORE TODAY AS IT REMAINS OVER RELATIVELY WARM WATER AND IN A
 MODERATE WIND SHEAR ENVIRONMENT.  HOWEVER...MUCH OF THE INTENSITY
 GUIDANCE SHOWS GRADUAL WEAKENING BEYOND 12 TO 24 HOURS AS JULIA
 MOVES OVER COOLER WATER AND THEN INTO STRONG NORTHERLY SHEAR
 ASSOCIATED WITH THE OUTFLOW OF HURRICANE IGOR.  THE NHC OFFICIAL
 INTENSITY FORECAST IS A LITTLE HIGHER THAN THE PREVIOUS
 ADVISORY...AND IS ABOVE ALL OF THE MODELS FOR THE FIRST FEW DAYS AS
 NONE OF THE GUIDANCE ANTICIPATED THE OBSERVED STRENGTHENING OF
 JULIA.
  
 THE HURRICANE HAS NOW TURNED TO THE NORTHWEST...WITH A 12-HOUR
 INITIAL MOTION ESTIMATE OF 305/9.  A CONTINUED NORTHWESTWARD MOTION
 IS EXPECTED FOR THE NEXT DAY OR SO AS JULIA NEARS A MID- TO
 UPPER-LEVEL TROUGH OVER THE EASTERN ATLANTIC.  HOWEVER...A TURN
 BACK TO THE WEST-NORTHWEST IS FORECAST IN ABOUT 36 HOURS AS THE
 HURRICANE IS STEERED BETWEEN AN UPPER-LEVEL LOW AND A STRENGTHENING
 SUBTROPICAL RIDGE.  JULIA IS EXPECTED TO APPROACH THE WESTERN
 PERIPHERY OF THE RIDGE IN 3 TO 4 DAYS ALLOWING THE SYSTEM TO TURN
 NORTHWARD AND POSSIBLY NORTH-NORTHEASTWARD BY DAY 5.  THE OFFICIAL
 TRACK FORECAST IS ADJUSTED SLIGHTLY TO THE RIGHT AND IS A LITTLE
 FASTER THAN THE PREVIOUS ONE TO COME INTO BETTER AGREEMENT WITH THE
 NEW GUIDANCE SUITE. 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      15/0900Z 17.3N  31.8W   115 KT
  12HR VT     15/1800Z 18.6N  33.2W   120 KT
  24HR VT     16/0600Z 20.4N  35.9W   120 KT
  36HR VT     16/1800Z 22.2N  39.3W   105 KT
  48HR VT     17/0600Z 23.4N  42.6W    95 KT
  72HR VT     18/0600Z 26.3N  48.1W    80 KT
  96HR VT     19/0600Z 30.0N  50.5W    65 KT
 120HR VT     20/0600Z 34.0N  49.5W    50 KT
  
 $$
 FORECASTER CANGIALOSI
  
 
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