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TROPICAL DEPRESSION ONE DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT MON JUL 27 1998

THE TROPICAL DEPRESSION HAS A LARGE BUT ELONGATED ENVELOPE AND IT
LACKS OF DEEP CONVECTION NEAR THE CENTER.  SINCE THE DEPRESSION IS
OVER WARM WATERS...THE OUTFLOW IS WELL ESTABLISHED AND HAS SUCH A
LARGE ENVELOPE...I HAVE NO CHOICE BUT...TO FORECAST STRENGTHENING.  
HOWEVER... SINCE THE GFDL DISSIPATES THE SYSTEM IN 12 HOURS AND
SHIPS MODEL BRINGS THE SYSTEM TO 49 KNOTS...ONLY A SLOW
STRENGTHENING IS INDICATED IN THE OFFICIAL FORECAST. 

THE LOW-LEVEL CENTER IS DIFFICULT TO LOCATE ON IR IMAGES AND THE
BEST ESTIMATE OF THE INITIAL MOTION IS 280/18.  ALL OF THE MODELS
THAT DEPEND ON THE AVN FORECAST FIELDS TURN THE DEPRESSION TO THE
NORTHWEST BY 48 HOURS.  THIS TURN IS CAUSED BY A DEVELOPING
MID-LEVEL TROUGH AHEAD OF THE SYSTEM WHICH IS FORECAST BY THE AVN. 
ON THE OTHER HAND...THE UK AND NOGAPS MODELS MAINTAIN MORE OF A 500
MB RIDGE TO THE NORTH OF THE TROPICAL CYCLONE.  THAT PATTERN WOULD
SUGGEST A WEST TO WEST NORTHWEST TRACK.  THE OFFICIAL FORECAST TRACK
IS TO THE LEFT OF MOST OF THE GUIDANCE BUT VERY CLOSE TO CLIPER.
THERE IS TIME TO ADJUST THE FORECAST TRACK MORE TO THE
NORTHWEST...IF NECESSARY.  

NOGAPS TRACKING ALGORITHM DROPS THE DEPRESSION IN 12 HOURS OR SO 
BUT AN INSPECTION OF LOW-LEVEL FIELDS FROM THE 12Z RUN...ONE CAN
OBSERVE A WEST TO WEST-NORTHWEST MOVING DISTURBANCE WHICH APPROACHES
THE LESSER ANTILLES IN 5 DAYS OR SO.   

AVILA 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     28/0300Z 12.5N  29.5W    25 KTS
12HR VT     28/1200Z 12.9N  32.2W    30 KTS
24HR VT     29/0000Z 13.5N  36.0W    35 KTS
36HR VT     29/1200Z 14.5N  39.0W    40 KTS
48HR VT     30/0000Z 15.5N  42.0W    45 KTS
72HR VT     31/0000Z 17.0N  47.5W    55 KTS
 
 
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