000
WTPZ44 KNHC 231442
TCDEP4
TROPICAL STORM FRANK DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092010
800 AM PDT MON AUG 23 2010
 
THE CONVECTIVE PATTERN ASSOCIATED WITH FRANK HAS ERODED CONSIDERABLY
NEAR THE CENTER AND IN THE EASTERN SEMICIRCLE DURING THE PAST FEW
HOURS DUE TO STRONG UPPER-LEVEL EAST-NORTHEASTERLY SHEAR OF AT
LEAST 25 KT. OBSERVATIONS FROM NOAA SHIP NWS0020 TO THE NORTH OF
AND SHIP A8SG2 SOUTHWEST OF THE CENTER ALSO INDICATE THAT THE WIND
FIELD HAS NOT EXPANDED AS FAR AS PREVIOUS EXPECTED. ALTHOUGH
SATELLITE INTENSITY ESTIMATES AT 1200 UTC WERE T3.5/55 KT FROM BOTH
TAFB AND SAB...THE INITIAL INTENSITY IS BEING HELD AT 50 KT DUE TO
THE AFOREMENTIONED DECREASE IN CENTRAL DEEP CONVECTION.
 
MICROWAVE FIX POSITIONS SUGGEST THE MOTION ESTIMATE IS 285/07. THE
MID-LEVEL RIDGE TO THE NORTH OF FRANK OVER THE U.S. SOUTHERN PLAINS
AND DESERT SOUTHWEST IS EXPECTED TO REMAIN INTACT THROUGH THE
FORECAST PERIOD. THIS FLOW PATTERN SHOULD KEEP FRANK MOVING IN A
GENERAL WEST-NORTHWESTWARD DIRECTION AND PARALLEL TO THE MEXICAN
COAST. BY DAY 5...THE WESTERN EXTENT OF THE RIDGE IS FORECAST TO
WEAKEN...WHICH SHOULD RESULT IN A DECREASE IN FORWARD SPEED AND
PERHAPS A SLIGHT TURN TOWARD THE NORTHWEST. THE OFFICIAL FORECAST
TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND THE MODEL CONSENSUS.
 
THE VERTICAL WIND SHEAR ACROSS THE CYCLONE IS NOT FORECAST TO ABATE
SIGNIFICANTLY FOR THE NEXT 48 HOURS OR SO. AS A RESULT...THE
INTENSITY FORECAST HAS BEEN TRIMMED BACK SLIGHTLY DURING THAT
PERIOD. HOWEVER...BY 72-96 HOURS...VERTICAL SHEAR IS EXPECTED TO
DECREASE TO AROUND 15 KT AND ALSO SWING AROUND TO THE EAST AND THEN
SOUTHEAST...WHICH SHOULD PROVIDE A SLIGHTLY MORE FAVORABLE
ENVIRONMENT FOR STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY
FORECAST IS A BLEND OF THE SHIPS/LGEM AND GFDL/HWRF INTENSITY
MODELS THROUGH 48 HOURS...AND THEN HIGHER THAN THE MODELS AFTER
THAT DUE TO THE EXPECTED DECREASE IN VERTICAL SHEAR.
 
BASED ON SHIP REPORTS INDICATING A SMALLER WIND FIELD...NO CHANGES
TO THE EXISTING TROPICAL STORM WARNING AND WATCH AREA FOR THE
PACIFIC COAST OF MEXICO ARE REQUIRED.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/1500Z 14.4N  98.2W    50 KT
 12HR VT     24/0000Z 14.7N  99.2W    55 KT
 24HR VT     24/1200Z 15.2N 100.7W    60 KT
 36HR VT     25/0000Z 15.9N 102.2W    60 KT
 48HR VT     25/1200Z 16.7N 103.9W    65 KT
 72HR VT     26/1200Z 17.9N 106.7W    65 KT
 96HR VT     27/1200Z 18.9N 109.6W    70 KT
120HR VT     28/1200Z 20.0N 112.0W    70 KT
 
$$
FORECASTER STEWART