220 
 WTNT42 KNHC 120300
 TCDAT2
 HURRICANE BERTHA DISCUSSION NUMBER  36
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
 1100 PM EDT FRI JUL 11 2008
  
 THE GEOSTATIONARY SATELLITE APPEARANCE OF BERTHA HAS NOT CHANGED
 THAT MUCH SINCE THE RECONNAISSANCE AIRCRAFT DEPARTED SEVERAL HOURS
 AGO...AND THE SUBJECTIVE DVORAK ESTIMATES ARE ABOUT THE SAME...SO
 THE ADVISORY INTENSITY REMAINS 80 KT.  BOTH INFRARED AND MICROWAVE
 IMAGERY SUGGEST THERE IS STILL SOMETHING OF AN INNER EYEWALL THAT
 REFUSES TO COMPLETELY GO AWAY...WHILE THE OUTER EYEWALL PERSISTS AS
 A CLOSED RING AT A SLIGHTLY SMALLER RADIUS THAN 24 HOURS AGO.  ALL
 OF THAT MEANS THAT THE WELL-ADVERTISED EYEWALL REPLACEMENT CYCLE IS
 NOT EXACTLY PROCEEDING AT A BLISTERING PACE...AND I AM REALLY NOT
 SURE HOW THE INNER CORE STRUCTURE WILL EVOLVE DURING THE NEXT 24
 HOURS OR SO.  PERSISTENCE MIGHT BE A GOOD GUIDE...SO A VERY SLOW
 CHANGE IN BERTHA'S STRUCTURE WILL BE THE ASSUMPTION DRIVING THE
 FLAT INTENSITY FORECAST THROUGH 24 HOURS.  VERY GRADUAL WEAKENING
 IS FORECAST THEREAFTER...IN ACCORDANCE WITH A CONSENSUS OF OUR
 PRIMARY INTENSITY MODELS...AS BERTHA TAKES ITS TIME MOVING TOWARD
 COOLER WATERS.  THE NEW OFFICIAL INTENSITY FORECAST IS ALMOST AN
 EXACT COPY OF THE PREVIOUS ONE.
 
 BERTHA IS CAUGHT IN A VERY WEAK STEERING REGIME AS IT CONTINUES
 MOVING...BARELY...AT 335/4.  THE DYNAMICAL MODELS DO NOT OFFER MUCH
 PROGNOSTIC EVIDENCE THAT A MID-LATITUDE TROUGH WITH SUFFICIENT
 AMPLITUDE WILL BE ABLE TO GET BERTHA MOVING MUCH FASTER WITHIN THE
 FIVE-DAY FORECAST PERIOD.  THE SHORTWAVE TROUGH CURRENTLY ALONG THE
 U.S. NORTHEAST COAST WILL ALMOST CERTAINLY BYPASS BERTHA WELL TO
 THE NORTH...AND NONE OF THE MODELS FORECAST BERTHA TO ACCELERATE
 AHEAD OF THE NEXT TROUGH WITHIN FIVE DAYS...ALTHOUGH THAT TROUGH
 LOOKS TO BE STRONGER AND MIGHT TRULY PICK UP BERTHA BEYOND THAT
 TIME.  IN BETWEEN THOSE TWO TROUGHS...THE MODELS DISAGREE ON HOW
 MUCH OF A RIDGE MIGHT FORM NORTH OF BERTHA...AND SOME OF THEM
 FORECAST BERTHA TO STALL WITHIN THE NEXT DAY OR TWO.  IN
 ADDITION...MOST OF THE MODELS SHOW AT LEAST SOME SOUTHWARD
 COMPONENT OF MOTION ON DAY 5...IN RESPONSE TO A CUTOFF LOW FORECAST
 TO BE NOT FAR NORTHEAST OF BERTHA BY THAT TIME.  THE RESULT OF THE
 COMPLICATED SET OF INDIVIDUAL MODEL TRACKS IS A CONSENSUS THAT
 LEADS ME TO SLOW DOWN THE OFFICIAL FORECAST JUST SLIGHTLY...ALSO
 WITH A NUDGE TO THE WEST...ALONG A TRACK SIMILAR TO THE PREVIOUS
 ADVISORY THAT SIMPLY BENDS BERTHA'S MOTION GRADUALLY TO THE
 RIGHT... AT A SPEED OF ABOUT 3 KT THROUGHOUT THE FIVE-DAY FORECAST. 
 SOME ERRATIC MOTION AT SOME POINT ALONG THE WAY WOULD NOT BE
 SURPRISING.
 
 THE PROBABILITY OF WINDS OF TROPICAL STORM FORCE OCCURRING IN
 BERMUDA WITHIN THE NEXT FIVE DAYS...AS CONVEYED IN THE WIND SPEED
 PROBABILITY PRODUCT INCLUDED IN EACH ADVISORY PACKAGE...HAS BEEN
 GRADUALLY RISING DURING THE PAST COUPLE OF DAYS...AND HAS NOW
 REACHED 58%.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      12/0300Z 29.4N  62.4W    80 KT
  12HR VT     12/1200Z 30.0N  62.6W    80 KT
  24HR VT     13/0000Z 30.6N  62.6W    80 KT
  36HR VT     13/1200Z 31.2N  62.5W    75 KT
  48HR VT     14/0000Z 31.7N  62.4W    70 KT
  72HR VT     15/0000Z 33.0N  62.0W    65 KT
  96HR VT     16/0000Z 34.0N  61.5W    60 KT
 120HR VT     17/0000Z 35.0N  60.5W    60 KT
  
 $$
 FORECASTER KNABB
  
 
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