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Tropical Storm FRANK


ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM FRANK DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092010
200 PM PDT TUE AUG 24 2010
 
FRANK HAS CONTINUED TO GET BETTER ORGANIZED TODAY AS INDICATED BY
IMPROVED BANDING FEATURES TO THE WEST AND EAST OF THE CENTER. THE
SMALL CENTRAL DENSE OVERCAST FEATURE NOTED EARLIER TODAY HAS ERODED
SOMEWHAT DURING THE PAST COUPLE OF HOURS. HOWEVER...THE CENTER
REMAINS EMBEDDED IN THE CONVECTION AT LEAST 35 NMI IN FROM THE
EASTERN EDGE OF THE CONVECTIVE CLOUD MASS. SATELLITE INTENSITY
ESTIMATES WERE T4.0/65 KT FROM TAFB AND T3.5/55 KT FROM SAB. NHC
3-HR AVERAGE ADT VALUES HAVE BEEN RUNNING BETWEEN T3.8/61 KT AND
T3.7/59 KT. PEAK ADT VALUES WERE T3.9/63 KT BETWEEN 15-16Z. BASED
ON THIS INFORMATION...THE INTENSITY IS NUDGED UPWARD TO 60 KT. A
1554Z ASCAT PASS WAS USED TO DEFINE THE 50- AND 34-KT WIND RADII.
 
THE INITIAL MOTION IS 285/07. THE SUBTROPICAL RIDGE TO THE NORTH OF
FRANK IS FORECAST TO KEEP THE CYCLONE MOVING WEST-NORTHWESTWARD
THROUGHOUT THE FORECAST PERIOD...WITH A GRADUAL DECREASE IN FORWARD
SPEED EXPECTED BY DAYS 4 AND 5 AS A MID-LEVEL TROUGH DIGS SOUTHWARD
AND WEAKENS THE WESTERN PERIPHERY OF THE RIDGE. THE GFDL MODEL...
WHICH HAD BEEN THE RIGHT-MOST OUTLIER MODEL WITH A TRACK FAIRLY
CLOSE TO MEXICO HAS SHIFTED WESTWARD AND IS NOW BACK IN THE FOLD AS
ONE OF THE LEFT-MOST MODELS IN THE GUIDANCE SUITE. THE OFFICIAL
FORECAST TRACK IS JUST AN UPDATE OF THE PREVIOUS ADVISORY TRACK AND
REMAINS BETWEEN THE CONSENSUS MODELS TVCN AND TVCC.
 
A SLIGHT INCREASE IN VERTICAL SHEAR COMBINED WITH SOME DRY AIR
ENTRAINMENT IN THE EASTERN SEMICIRCLE APPEARS TO HAVE WEAKENED THE
CENTRAL CONVECTION DURING THE PAST FEW HOURS. HOWEVER...MODEST
CONVECTION THAT IS DEVELOPING IN THE DRY SLOT SUGGESTS THAT THE
EFFECTS OF THE DRY AIR SHOULD BE SHORT-LIVED. FRANK IS ALSO MOVING
INTO A REGION OF LOWER VERTICAL SHEAR BASED ON UW-CIMSS SHEAR
ANALYSES AND WATER VAPOR-DERIVED WINDS. THE GFS AND ECMWF MODELS
CONTINUE TO FORECAST FRANK TO DEVELOP AN UPPER-LEVEL ANTICYCLONE
OVER THE SYSTEM BY 36 HOURS...WHICH WOULD EASILY SUPPORT FORMATION
OF A HURRICANE...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST.
EVEN THE GFDL MODEL BRINGS FRANK UP TO 74 KT BY 36 HOURS. BY DAY
4...FRANK SHOULD BE MOVING OVER SUB-26C SSTS...WHICH SHOULD CAUSE
GRADUAL WEAKENING TO ENSUE. THE OFFICIAL INTENSITY FORECAST IS
SIMILAR TO THE SHIPS AND LGEM INTENSITY MODELS THROUGH 24 HOURS...
AND HIGHER THAN THOSE MODELS AFTER THAT BASED ON THE FAVORABLE
UPPER-LEVEL OUTFLOW PATTERN FORECAST TO DEVELOP OVER THE CYCLONE. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/2100Z 15.6N 102.1W    60 KT
 12HR VT     25/0600Z 16.1N 103.4W    60 KT
 24HR VT     25/1800Z 16.8N 105.1W    65 KT
 36HR VT     26/0600Z 17.4N 106.7W    70 KT
 48HR VT     26/1800Z 18.1N 108.5W    75 KT
 72HR VT     27/1800Z 19.3N 111.2W    75 KT
 96HR VT     28/1800Z 20.2N 112.6W    65 KT
120HR VT     29/1800Z 21.5N 113.5W    55 KT
 
$$
FORECASTER STEWART
 
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