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 386 
 WTNT42 KNHC 122034
 TCDAT2
 TROPICAL DEPRESSION TWO DISCUSSION NUMBER   7
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022009
 500 PM AST WED AUG 12 2009
 
 THE DEPRESSION APPEARED TO BE ON THE VERGE OF BECOMING A TROPICAL
 STORM A FEW HOURS AGO...WITH SATELLITE INTENSITY ESTIMATES OF 35 KT
 FROM TAFB AND SAB.  HOWEVER...SINCE ABOUT 18Z THE CONVECTION HAS
 DECREASED SIGNIFICANTLY AND HAS MOVED FARTHER AWAY FROM THE EXPOSED
 LOW-LEVEL CENTER.  BASED ON THIS...THE CYCLONE WILL REMAIN A 30 KT
 DEPRESSION FOR THIS ADVISORY.  THE CURRENT DOWNWARD TREND IN THE
 CONVECTION MAY BE DUE TO AN INCREASE IN EASTERLY VERTICAL WIND
 SHEAR...AND TO A DRY SLOT WRAPPING AROUND THE CIRCULATION NOTED IN
 AMSR-E VAPOR IMAGERY NEAR 1534Z.  ALSO...AS SEEN EARLIER...MOST OF
 THE LOW-LEVEL INFLOW INTO THE DEPRESSION SEEMS TO BE COMING FROM
 THE NORTH...REPRESENTING POSSIBLY MORE STABLE AIR PASSING OVER
 COOLER WATERS.  THE FLOW ON THE SOUTH SIDE OF THE DEPRESSION IS
 FEEDING INTO A LARGE DISTURBANCE BETWEEN THE CAPE VERDE ISLANDS AND
 AFRICA.
  
 THE INITIAL MOTION IS 265/12.  THE DEPRESSION IS ON THE SOUTH
 SIDE OF A LARGE LOW/MID-LEVEL RIDGE...AND THE LARGE-SCALE MODELS
 FORECAST THIS TO CONTINUE FOR THE NEXT TWO DAYS OR SO.  AFTER THAT
 TIME...THE MODELS FORECAST A WEAKNESS IN THE RIDGE THAT WOULD STEER
 THE CYCLONE WEST-NORTHWESTWARD.  THE TRACK MODEL GUIDANCE GENERALLY
 AGREES WITH THIS SCENARIO...AND WHILE THE MODEL CLUSTERS SEEN
 EARLIER HAVE MERGED THERE IS STILL A SIGNIFICANT SPREAD BY 120 HR.
 THE GFS AND UKMET ARE ON THE SOUTH SIDE OF THE GUIDANCE ENVELOPE
 SHOWING A MORE WESTERLY MOTION...WHILE THE HWRF AND BAMD ARE ON THE
 NORTH SIDE SHOWING A NORTHWESTWARD MOTION BY 120 HR.  OVERALL...THE
 GUIDANCE ENVELOPE HAS AGAIN SHIFTED A LITTLE SOUTHWARD...AND SO HAS
 THE NEW OFFICIAL FORECAST.  THE NEW TRACK IS IN THE CENTER OF THE
 GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE TVCN AND TVCC
 CONSENSUS MODELS.
  
 THE DEPRESSION REMAINS OVER SEA SURFACE TEMPERATURES NEAR 27C...WITH
 SSTS ALONG THE FORECAST TRACK INCREASING TO 28C AFTER 72 HR.  THE
 LARGE-SCALE MODELS FORECAST THE DEPRESSION TO ENCOUNTER MODERATE
 VERTICAL WIND SHEAR DURING THE FORECAST PERIOD...FIRST FROM THE
 EAST AND LATER FROM THE SOUTHWEST.  ALSO...WATER VAPOR IMAGERY
 SHOWS VERY DRY AIR AT THE MID/UPPER-LEVELS TO THE NORTHWEST OF THE
 DEPRESSION.  THE LATTER TWO FACTORS SUGGEST THE SYSTEM MAY BE SLOW
 TO STRENGTHEN...AND NONE OF THE INTENSITY GUIDANCE CURRENTLY
 FORECASTS AN INTENSITY GREATER THAN 55 KT DURING THE FORECAST
 PERIOD.  BASED ON THIS...THE NEW INTENSITY FORECAST IS AN UPDATE OF
 THE PREVIOUS FORECAST IN BEST AGREEMENT WITH THE SHIPS MODEL.  IT
 IS POSSIBLE THAT THE SYSTEM COULD WEAKEN TO A TROPICAL WAVE DURING
 THE FORECAST PERIOD...AS FORECAST BY THE ECMWF...UKMET...AND GFS
 MODELS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      12/2100Z 14.3N  35.0W    30 KT
  12HR VT     13/0600Z 14.1N  36.7W    35 KT
  24HR VT     13/1800Z 14.1N  38.9W    35 KT
  36HR VT     14/0600Z 14.2N  41.3W    40 KT
  48HR VT     14/1800Z 14.6N  43.7W    45 KT
  72HR VT     15/1800Z 16.0N  49.5W    50 KT
  96HR VT     16/1800Z 19.0N  56.0W    50 KT
 120HR VT     17/1800Z 23.0N  62.0W    45 KT
  
 $$
 FORECASTER BEVEN
  
 
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