334 
 WTNT42 KNHC 060851
 TCDAT2
 TROPICAL STORM BERTHA DISCUSSION NUMBER  13
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
 500 AM EDT SUN JUL 06 2008
 
 NOT MANY CHANGES TO REPORT WITH BERTHA THIS MORNING. THE CYCLONE
 CONTINUES TO MOVE QUICKLY WESTWARD ALONG A HEADING OF ABOUT 280/19
 TO THE SOUTH OF THE SUBTROPICAL RIDGE. THE OBJECTIVE GUIDANCE IS IN
 VERY GOOD AGREEMENT THROUGH ABOUT 48 HOURS ON A GENERAL
 WEST-NORTHWESTWARD MOTION...AND A GRADUAL SLOWING OF THE FORWARD
 SPEED AS HEIGHTS BUILD TO THE NORTHWEST OF BERTHA OVER THE
 SUBTROPICAL WESTERN ATLANTIC. THE MODELS STILL DIVERGE
 SIGNIFICANTLY AT DAYS 3 THROUGH 5...BUT THEY HAVE GENERALLY COME
 INTO A LITTLE BETTER AGREEMENT ON A TURN TOWARD THE NORTHWEST BY
 THEN...ALTHOUGH AT A FORWARD SPEED OF ABOUT HALF OF BERTHA'S
 CURRENT MOTION. THE OUTLIER IS THE HWRF THAT FORECASTS A MUCH
 SOONER TURN TOWARD THE NORTH ALONG ABOUT 58W. NONE OF THE
 MODELS...HOWEVER...FORECAST BERTHA TO REACH 30 DEGREES NORTH
 LATITUDE WITHIN FIVE DAYS. WHILE THE RIDGE OVER THE WESTERN
 ATLANTIC IS FORECAST TO BE MUCH WEAKER BY THE END OF THE FIVE-DAY
 FORECAST PERIOD...THE MODELS DO NOT DEPICT A HIGH-AMPLITUDE TROUGH
 THAT WOULD ACCELERATE BERTHA INTO THE MIDDLE LATITUDES. SO IT IS
 FAR TOO EARLY TO DETERMINE IF OR WHEN BERTHA WILL RECURVE. THE NEW
 OFFICIAL TRACK FORECAST IS ADJUSTED SLIGHTLY TO THE RIGHT...TOWARD
 BUT NOT AS FAR EAST AS THE CONSENSUS.
 
 THE WATERS BENEATH BERTHA ARE CURRENTLY ABOUT 26 CELSIUS AND
 CONTINUE TO GET WARMER AS THE CYCLONE PROCEEDS WESTWARD...AND BY 48
 HOURS FROM NOW THEY SHOULD BE APPROACHING 28 CELSIUS.  VERTICAL
 WIND SHEAR SHOULD NOT STRENGTHEN DURING THIS PERIOD...SO GRADUAL
 STRENGTHENING IS FORECAST IN LINE WITH NEARLY ALL OF THE OBJECTIVE
 INTENSITY GUIDANCE...AND BERTHA COULD BE A HURRICANE IN A COUPLE OF
 DAYS.  BEYOND THAT TIME...THE WATERS WILL BE PLENTY WARM...SO THE
 DETERMINING FACTOR ON THE INTENSITY OF BERTHA WILL PROBABLY BE WIND
 SHEAR.  THE UPPER-LEVEL PATTERN FORECAST BY THE MODELS AT DAYS 3
 THROUGH 5 IS COMPLEX...AND IT IS HARD TO DETERMINE JUST HOW MUCH
 SHEAR WILL BE AFFECTING BERTHA DURING THAT PERIOD.  DESPITE TAKING
 INTO ACCOUNT A MODEST INCREASE IN SHEAR BASED ON THE GFS MODEL WIND
 FIELDS...THE SHIPS AND LGEM FORECAST 70-75 KT AT 72-120 HOURS...SO
 THE NEW OFFICIAL INTENSITY FORECAST PEAKS AT 70 KT...A LITTLE
 HIGHER THAN THE PREVIOUS ADVISORY.  GIVEN THE UNCERTAINTIES IN THE
 ATMOSPHERIC PATTERN AT THOSE LONG RANGES...HOWEVER...THIS IS NOT A
 HIGH CONFIDENCE INTENSITY FORECAST.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      06/0900Z 17.3N  43.2W    45 KT
  12HR VT     06/1800Z 17.9N  46.1W    50 KT
  24HR VT     07/0600Z 18.7N  49.5W    55 KT
  36HR VT     07/1800Z 19.6N  52.5W    60 KT
  48HR VT     08/0600Z 20.4N  55.1W    65 KT
  72HR VT     09/0600Z 22.5N  60.0W    70 KT
  96HR VT     10/0600Z 24.5N  64.0W    70 KT
 120HR VT     11/0600Z 27.0N  67.5W    70 KT
  
 $$
 FORECASTER KNABB