964 
 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