000
WTPZ43 KNHC 071433
TCDEP3
TROPICAL STORM BLANCA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP032009
800 AM PDT TUE JUL 07 2009
 
ALTHOUGH THE CLOUD PATTERN AND UPPER-LEVEL OUTFLOW ASSOCIATED WITH
BLANCA REMAINS WELL-ESTABLISHED...DEEP CONVECTION HAS GRADUALLY
BEEN DIMINISHING.  IN FACT...THE MOST SIGNIFICANT AREA OF
CONVECTION COMPRISES A BAND TO THE SOUTHEAST OF THE CENTER...WITH
PULSATING DEEP CONVECTION SURROUNDING THE CENTER RATHER SPARSE.
THE LACK OF DEEP CONVECTION HAS CAUSED DVORAK T-NUMBERS TO SLOWLY
DECREASE...WITH THE LATEST ESTIMATES OF 2.0 AND 2.5 FROM SAB AND
TAFB... RESPECTIVELY. BASED UPON THESE...THE INITIAL INTENSITY IS
REDUCED TO 40 KT THIS ADVISORY.
 
THE CYCLONE HAS ENTERED SUB-26C SSTS...AND THE SHIPS MODEL SHOWS
SSTS TO DECREASE TO AS LOW AS 23-24C ALONG THE FORECAST TRACK
WITHIN 24 HOURS. MOREOVER...BLANCA SHOULD ENCOUNTER AND INGEST MORE
STABLE BOUNDARY LAYER AIR AND WILL BE SUBJECT TO MODEST EASTERLY
SHEAR.  THE ABOVE CONDITIONS SUGGEST THAT THE CURRENT WEAKENING
TREND WILL CONTINUE AND POSSIBLY ACCELERATE OVER THE NEXT DAY OR
TWO.  IT IS POSSIBLE THAT BLANCA COULD DEGENERATE INTO A REMNANT
LOW SOONER THAN FORECAST...GIVEN THE INCREASING NEGATIVE FACTORS.
 
RECENT SATELLITE FIXES YIELD AND ESTIMATED MOTION OF 295/09.  THE
TRACK PHILOSOPHY IS UNCHANGED.  A BROAD BUT FLAT MID-LEVEL RIDGE
EXTENDING FROM THE DESERT SOUTHWEST INTO THE SUBTROPICAL EAST
PACIFIC WILL STEER BLANCA ON A GENERALLY WEST-NORTHWESTWARD
COURSE...WITH A GRADUAL DECREASE IN FORWARD SPEED AFTER 36 HOURS AS
BOTH THE CYCLONE AND THE RIDGE WEAKEN.  THEREAFTER...MODELS HAVE
TRENDED NORTH FROM YESTERDAY'S RUNS...AS BLANCA NEARS THE WESTERN
EDGE OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE.  AS A RESULT...THE
FORECAST TRACK HAS BEEN GRADUALLY NUDGED FARTHER NORTHWEST THE LAST
SEVERAL ADVISORIES PRIOR TO DISSIPATION.
 
OBSERVATIONS FROM CLARION ISLAND...TIMELY PROVIDED BY THE MEXICAN
NAVY...HELPED TO MONITOR TROPICAL STORM BLANCA.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      07/1500Z 19.0N 115.8W    40 KT
 12HR VT     08/0000Z 19.5N 117.2W    35 KT
 24HR VT     08/1200Z 20.2N 118.8W    30 KT
 36HR VT     09/0000Z 20.8N 120.2W    25 KT
 48HR VT     09/1200Z 21.3N 121.4W    20 KT...REMNANT LOW
 72HR VT     10/1200Z 22.0N 123.5W    20 KT...REMNANT LOW
 96HR VT     11/1200Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN/AVILA