WTNT44 KNHC 131458
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
1100 AM EDT MON AUG 13 2007
 
METEOSAT-9 VISIBLE AND INFRARED IMAGERY DURING THE PAST SEVERAL
HOURS REVEALS THAT THE LOW PRESSURE AREA OVER THE FAR EASTERN
TROPICAL ATLANTIC HAS BECOME A TROPICAL DEPRESSION.  THE DEEP
CONVECTION HAS BEEN PERSISTENT FOR MORE THAN 12 HOURS...BUT IT IS
MOSTLY CONFINED WEST OF THE CIRCULATION CENTER DUE TO MODERATE
EASTERLY WIND SHEAR.  A QUIKSCAT OVERPASS AT 0723Z THIS MORNING
ONLY CAPTURED THE EASTERN SEMICIRCLE BUT AN AMBIGUITY ANALYSIS
INDICATES SOME BELIEVABLE 30-KT WINDS.  DVORAK INTENSITY ESTIMATES
BASED ON THE CURVED BAND PATTERN AT 12Z WERE 25-30 KT...ALTHOUGH THE
DEPTH AND COVERAGE OF CONVECTION HAVE DECREASED SINCE 12Z.  THE
ADVISORY INTENSITY IS SET TO 30 KT.

THE LOW-LEVEL CENTER HAS BEEN MOVING SLIGHTLY SOUTH OF DUE WEST THIS
MORNING...AND THE INITIAL MOTION ESTIMATE IS 265/18...BUT MORE
RECENT VISIBLE AND MICROWAVE IMAGES SUGGEST THE CENTER MIGHT BE
EVEN A LITTLE FARTHER SOUTH THAN THE ADVISORY POSITION.  WITH THE
DEEP-LAYER RIDGE NORTH OF THE CYCLONE FORECAST TO STRENGTHEN AND
BUILD WESTWARD...A SLIGHT SOUTHWARD COMPONENT OF MOTION MIGHT
PERSIST FOR A COUPLE OF DAYS...BUT THE TRACK SHOULD BE GENERALLY
WESTWARD AND FAIRLY BRISK.  A VERY GRADUAL BEND TO THE RIGHT AND A
SLIGHTLY SLOWER FORWARD SPEED ARE FORECAST TO BEGIN ON DAY THREE AS
THE RIDGE WEAKENS...BUT ONLY SLIGHTLY.  THE OFFICIAL FORECAST TRACK
IS A BLEND OF THE GFDL...UKMET...AND GFS.

THE EASTERLY WIND SHEAR WILL PROBABLY LIMIT INTENSIFICATION DURING
THE NEXT COUPLE OF DAYS.  THEREAFTER...THE GLOBAL MODELS...EVEN
THOSE THAT DO NOT HAVE A STRONG REPRESENTATION OF THE TROPICAL
CYCLONE ITSELF...FORECAST AN UPPER-LEVEL RIDGE TO BUILD OVER AND
NEAR THE LESSER ANTILLES.  COMBINED WITH WARM SEA-SURFACE
TEMPERATURES ALONG THE TRACK...CONDITIONS APPEAR CONDUCIVE FOR
STEADY STRENGTHENING LATER IN THE FORECAST PERIOD.  THE SHIPS
GUIDANCE FORECASTS NEARLY HURRICANE STRENGTH BY 72 HOURS...AND THE
GFDL FORECAST INTENSITY EXCEEDS 100 KT AT FIVE DAYS.  THE OFFICIAL
FORECAST IS CLOSE TO THE SHIPS GUIDANCE FOR THE FIRST THREE
DAYS...THEN INDICATES A STRENGTHENING HURRICANE...BUT IS NOT AS
AGGRESSIVE AS THE GFDL.

IT IS IMPORTANT TO REMEMBER THAT SIGNIFICANT UNCERTAINTIES EXIST IN
BOTH THE TRACK AND INTENSITY FORECASTS...ESPECIALLY AT LONG RANGES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/1500Z 12.0N  31.6W    30 KT
 12HR VT     14/0000Z 12.0N  34.3W    35 KT
 24HR VT     14/1200Z 11.9N  38.0W    40 KT
 36HR VT     15/0000Z 11.9N  41.4W    45 KT
 48HR VT     15/1200Z 11.9N  44.7W    50 KT
 72HR VT     16/1200Z 13.0N  51.0W    60 KT
 96HR VT     17/1200Z 14.5N  57.5W    75 KT
120HR VT     18/1200Z 16.0N  63.5W    90 KT
 
$$
FORECASTER KNABB
 

WTNT44 KNHC 132054
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 PM EDT MON AUG 13 2007
 
THE DEPRESSION IS MAINTAINING ITSELF IN THE FACE OF EASTERLY WIND
SHEAR OF ABOUT 15 KT. DEEP CONVECTION HAS BEEN PULSATING TODAY AND
HAS REMAINED DISPLACED TO THE WEST OF THE LOW-LEVEL CENTER.
METEOSAT-9 HIGH-RESOLUTION VISIBLE IMAGERY CLEARLY REVEALED THE
EXPOSED LOW-LEVEL CENTER EARLIER THIS AFTERNOON...BUT MORE RECENTLY
THE CONVECTION HAS INCREASED AND PARTIALLY OBSCURED THE CENTER.
DVORAK INTENSITY ESTIMATES ARE UNCHANGED AND THE ADVISORY INTENSITY
REMAINS 30 KT.

TD FOUR IS STILL RACING ALMOST DUE WESTWARD...WITH AN INITIAL MOTION
ESTIMATE OF 265/17. A CONTINUED BRISK AND GENERALLY WESTWARD MOTION
SHOULD CONTINUE DURING THE NEXT COUPLE OF DAYS WHILE THE CYCLONE
MOVES ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYER RIDGE. THE
OFFICIAL FORECAST IS AHEAD OF NEARLY ALL OF THE GUIDANCE DURING
THAT PERIOD...AS THE MODELS DO NOT SEEM TO HAVE A GOOD HANDLE ON
THE FAST INITIAL SPEED. BEYOND 48 HOURS...A TURN TOWARD THE
WEST-NORTHWEST IS FORECAST BY ALL OF THE MODELS. SINCE THIS
MORNING...ALL OF THE TRACK MODEL GUIDANCE HAS SLOWED DOWN AND
SHIFTED TO THE RIGHT...IN RESPONSE TO FORECASTING A SLIGHTLY WEAKER
SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC LATER IN THE FORECAST
PERIOD. THE NEW OFFICIAL TRACK HAS BEEN ADJUSTED TOWARD THE
CONSENSUS OF THE LATEST MODELS...BUT REMAINS A LITTLE FASTER AND TO
THE WEST OF THE GUIDANCE ENVELOPE...SINCE THE GUIDANCE COULD SHIFT
BACK THE OTHER WAY LATER.

THE SHEAR IS FORECAST TO ABATE WHILE THE SEA-SURFACE TEMPERATURES
WILL INCREASE ALONG THE OFFICIAL TRACK DURING THE NEXT 2-3 DAYS.
THEREAFTER...MOST OF THE GLOBAL MODELS FORECAST THE TROPICAL
CYCLONE TO FIND ITSELF BENEATH AN UPPER-LEVEL RIDGE...AN
ENVIRONMENT THAT WOULD FAVOR STRENGTHENING. A NOTABLE EXCEPTION IS
THE ECMWF...WHICH FORECASTS A STRONGER MID-OCEANIC TROUGH OVER THE
CENTRAL ATLANTIC IN 4-5 DAYS WHICH COULD CAUSE AN INCREASE IN THE
SHEAR.  THAT MODEL...HOWEVER...DOES NOT REPRESENT THE TROPICAL
CYCLONE WELL...AND IT MIGHT NOT HAVE GOOD HANDLE ON HOW THE CYCLONE
COULD MODIFY THE UPPER-LEVEL FLOW. THE SHIPS GUIDANCE FORECASTS 63
KT AT 72 HOURS AND 75 KT BY FIVE DAYS...WHILE THE LGEM REACHES 84
KT AT 120 HOURS. MEANWHILE THE GFDL AND HWRF FORECAST 90 AND 84
KT...RESPECTIVELY...AT FIVE DAYS. CONSIDERING THIS GUIDANCE...THE
NEW OFFICIAL INTENSITY FORECAST IN UNCHANGED FROM THIS MORNING BUT
RETAINS A SIGNIFICANT AMOUNT OF UNCERTAINTY...ESPECIALLY AT THE
LONGER RANGES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      13/2100Z 11.9N  33.1W    30 KT
 12HR VT     14/0600Z 11.8N  35.5W    35 KT
 24HR VT     14/1800Z 11.8N  38.5W    40 KT
 36HR VT     15/0600Z 11.8N  41.6W    45 KT
 48HR VT     15/1800Z 12.1N  44.7W    50 KT
 72HR VT     16/1800Z 13.0N  50.5W    60 KT
 96HR VT     17/1800Z 15.0N  56.0W    75 KT
120HR VT     18/1800Z 17.0N  61.0W    90 KT
 
$$
FORECASTER KNABB
 

WTNT44 KNHC 140251
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
1100 PM EDT MON AUG 13 2007
 
THE ORGANIZATION OF THE DEPRESSION HAS CERTAINLY NOT IMPROVED THIS
EVENING.  THE OVERALL CONVECTIVE ENVELOPE APPEARS TO HAVE BECOME
ELONGATED EAST TO WEST AS THE DEPRESSION CONTINUES TO BE PLAGUED BY
STRONG UPPER-LEVEL EASTERLY WINDS.  A QUIKSCAT PASS DURING THE
AFTERNOON CAUGHT THE EASTERN PORTION OF THE CIRCULATION AND IT
SUGGESTS THAT THE MAXIMUM WINDS REMAIN NEAR 30 KT. THE LATEST
DVORAK SATELLITE INTENSITY ESTIMATE ALSO SUPPORT 30 KT AND THE
CYCLONE WILL REMAIN A DEPRESSION FOR THIS ADVISORY.

THE DEPRESSION CONTINUES TO MOVE BRISKLY WESTWARD...WITH AN INITIAL
MOTION ESTIMATE OF 270/17.  THE CYCLONE IS EXPECTED TO CONTINUE
MOVING WESTWARD DURING THE NEXT COUPLE OF DAYS...SOUTH OF A DEEP
LAYER RIDGE.  THE OFFICIAL FORECAST CONTINUES TO BE FASTER THAN
VIRTUALLY ALL OF THE GUIDANCE DURING THAT TIME PERIOD. 
THEREAFTER...MOST OF THE MODELS INDICATE THAT THE SUBTROPICAL RIDGE
WILL WEAKEN OVER THE CENTRAL ATLANTIC...ALLOWING THE CYCLONE TO
TURN WEST-NORTHWESTWARD.  THE GFDL AND HWRF REMAIN ON THE RIGHT
SIDE OF THE GUIDANCE ENVELOPE...SHOWING AN EARLIER TURN TOWARD THE
WEST-NORTHWEST.  THE NEW OFFICIAL TRACK IS CLOSE TO THE GFS AND
UKMET SOLUTIONS AND IS VERY CLOSE TO THE PREVIOUS NHC TRACK.
 
THE INTENSITY FORECAST PHILOSOPHY REMAINS UNCHANGED FROM THE
PREVIOUS ADVISORY.  MOST OF THE GUIDANCE SUGGESTS THAT THE SHEAR
WILL DECREASE DURING THE NEXT COUPLE OF DAYS ALLOWING THE CYCLONE TO
GRADUALLY STRENGTHEN.  THE EXPLICIT INTENSITY GUIDANCE IS IN
REMARKABLY GOOD AGREEMENT AND THE OFFICIAL FORECAST IS UNCHANGED
FROM THE PREVIOUS ADVISORY.  
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0300Z 12.0N  35.0W    30 KT
 12HR VT     14/1200Z 12.0N  37.4W    35 KT
 24HR VT     15/0000Z 12.0N  40.4W    40 KT
 36HR VT     15/1200Z 12.2N  43.4W    45 KT
 48HR VT     16/0000Z 12.6N  46.4W    50 KT
 72HR VT     17/0000Z 13.8N  52.0W    60 KT
 96HR VT     18/0000Z 16.0N  57.5W    75 KT
120HR VT     19/0000Z 18.5N  62.5W    90 KT
 
$$
FORECASTER BROWN/FRANKLIN
 

WTNT44 KNHC 140838
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 AM EDT TUE AUG 14 2007
 
LATEST SATELLITE IMAGERY INDICATES THAT THERE HAS BEEN LITTLE
OVERALL CHANGE IN THE ORGANIZATION OR THE STRUCTURE OF THE
DEPRESSION.  THE LOW-LEVEL CIRCULATION IS STILL NOT WELL-DEFINED
AND IS ELONGATED EAST TO WEST WITH ALL OF THE DEEP CONVECTION
DISPLACED WEST OF THE ESTIMATED CENTER.  THE INITIAL INTENSITY
REMAINS 30 KT FOR THIS ADVISORY IN CONCURRENCE WITH DVORAK
ESTIMATES FROM BOTH TAFB AND SAB.  GLOBAL MODELS ALL INDICATE THAT
THE SHEAR WILL GRADUALLY RELAX OVER THE NEXT COUPLE OF DAYS AND AN
UPPER-LEVEL ANTICYCLONE WILL BUILD OVER THE CYCLONE.
THIS...COMBINED WITH INCREASINGLY WARMER WATERS ALONG THE FORECAST
TRACK...SHOULD CREATE A MORE FAVORABLE ENVIRONMENT FOR
INTENSIFICATION.  THE GFDL... HWRF...AND SHIPS MODELS ARE NOW
FORECASTING PEAK INTENSITIES OF 110 KT...104 KT...AND 92 KT
RESPECTIVELY.  HOWEVER...CONSIDERING THE PRESENT LACK OF
ORGANIZATION...THE OFFICIAL FORECAST STAYS NEAR THE LOWER END OF
THE AVAILABLE INTENSITY GUIDANCE AND IS PRACTICALLY UNCHANGED FROM
THE PREVIOUS ADVISORY. 
 
UNDER THE INFLUENCE OF A STRONG DEEP-LAYER RIDGE TO THE NORTH...THE
DEPRESSION CONTINUES TO MOVE RAPIDLY WESTWARD OR 270/18.  THIS
GENERAL MOTION IS LIKELY TO CONTINUE DURING THE NEXT DAY OR TWO. 
THEREAFTER...A WEAKNESS IN THE RIDGE OVER THE CENTRAL ATLANTIC
SHOULD CAUSE A GRADUAL TURN TOWARD THE WEST-NORTHWEST WITH A
REDUCTION IN FORWARD SPEED.  BY DAYS 4-5...MODELS BEGIN TO DIVERGE
DUE TO DIFFERING FORECASTS OF AN MID/UPPER-LEVEL CUTOFF LOW
EXPECTED TO FORM OFF THE SOUTHEASTERN UNITED STATES COAST.  THE
UKMET QUICKLY DISSIPATES THE LOW...ALLOWING MID-LEVEL RIDGING TO
BUILD OVER THE WESTERN ATLANTIC.  CONVERSELY...THE GFS SHOWS THE
MID/UPPER-LEVEL LOW REMAINING STATIONARY...PRODUCING A GAP IN THE
SUBTROPICAL RIDGE.  THE LATEST OFFICIAL FORECAST IS NUDGED TOWARD
THE MODEL CONSENSUS AND IS A LITTLE SOUTH OF...AND SLIGHTLY SLOWER
THAN...THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0900Z 12.0N  36.8W    30 KT
 12HR VT     14/1800Z 12.0N  39.3W    35 KT
 24HR VT     15/0600Z 12.1N  42.1W    40 KT
 36HR VT     15/1800Z 12.3N  45.0W    45 KT
 48HR VT     16/0600Z 12.7N  47.9W    55 KT
 72HR VT     17/0600Z 14.0N  53.5W    65 KT
 96HR VT     18/0600Z 16.0N  59.0W    80 KT
120HR VT     19/0600Z 18.5N  63.5W    90 KT
 
$$
FORECASTER RHOME
 

