000
WTPZ43 KNHC 182034
TCDEP3
TROPICAL STORM BLAS DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP032010
200 PM PDT FRI JUN 18 2010
 
VISIBLE IMAGERY SHOWS THAT THE LOW-LEVEL CENTER OF BLAS IS LOCATED
AT THE NORTHEASTERN EDGE OF THE MAIN CONVECTIVE REGION.  A RECENT
ASCAT SCATTEROMETER OVERPASS SHOWS 35-40 KT WINDS SOUTH OF THE
CENTER...SO THE INITIAL INTENSITY REMAINS 40 KT.  THE STORM
CONTINUES TO EXPERIENCE LIGHT/MODERATE NORTHEASTERLY VERTICAL WIND
SHEAR...WITH FAIR CIRRUS OUTFLOW IN THE SOUTHWESTERN SEMICIRCLE AND
POOR/NONE ELSEWHERE.
 
THE LARGE-SCALE MODELS STILL FORECAST THE SHEAR TO DECREASE DURING
THE NEXT 48-72 HR.  HOWEVER...THE FORECAST TRACK TAKES BLAS OVER
STEADILY DECREASING SEA SURFACE TEMPERATURES.  THE LATTER SHOULD
CAUSE THE STORM TO SLOWLY WEAKEN...WITH THE INTENSITY FORECAST
CALLING FOR BLAS TO BECOME A TROPICAL DEPRESSION IN ABOUT 48 HR AND
A REMNANT LOW IN ABOUT 96 HR.  THE NEW INTENSITY FORECAST IS IN
BEST AGREEMENT WITH...ALTHOUGH A LITTLE BELOW...THE INTENSITY
CONSENSUS.
 
THE INITIAL MOTION IS NOW 290/5.  BLAS REMAINS ON THE SOUTH SIDE OF
A MID-LEVEL RIDGE EXTENDING WESTWARD FROM MEXICO...AND THE
LARGE-SCALE MODELS FORECAST THIS FEATURE TO PERSIST WITH LITTLE
CHANGE IN STRENGTH THROUGH THE FORECAST PERIOD.  A LOW-LEVEL RIDGE
IS FORECAST TO BUILD NORTH AND WEST OF THE CYCLONE AFTER 72 HR. 
THE TRACK GUIDANCE RESPONDS TO THIS BY SHOWING THE CURRENT WEST-
NORTHWESTWARD MOTION BECOMING WESTWARD DURING THE NEXT COUPLE OF
DAYS...AND WEST-SOUTHWESTWARD AT ABOUT 72 HR.  THE NEW FORECAST
TRACK IS SIMILAR TO THE PREVIOUS TRACK.  HOWEVER...THE GUIDANCE
ENVELOPE HAS SHIFTED A LITTLE TO THE NORTH SINCE THE LAST
PACKAGE...AND THE FORECAST TRACK NOW LIES ALONG OR JUST SOUTH OF
THE MODEL CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/2100Z 16.1N 108.0W    40 KT
 12HR VT     19/0600Z 16.3N 108.8W    40 KT
 24HR VT     19/1800Z 16.6N 110.2W    35 KT
 36HR VT     20/0600Z 16.8N 111.9W    35 KT
 48HR VT     20/1800Z 16.9N 113.6W    30 KT
 72HR VT     21/1800Z 17.0N 117.0W    25 KT
 96HR VT     22/1800Z 16.5N 120.0W    25 KT...POST-TROP/REMNT LOW
120HR VT     23/1800Z 16.0N 123.5W    20 KT...POST-TROP/REMNT LOW
 
$$
FORECASTER BEVEN