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Hurricane DARBY


ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM DARBY DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT FRI JUL 30 2004
 
DARBY IS NOW A WELL-DEFINED SWIRL OF LOW/MID LEVEL CLOUDS WITH
ISOLATED PATCHES OF DEEP CONVECTION TO THE NORTHEAST OF THE CENTER. 
AS IS OFTEN THE CASE...IT IS DIFFICULT TO ASCERTAIN THE INTENSITY
OF THIS TYPE OF SYSTEM.  SATELLITE INTENSITY ESTIMATES ARE 65 KT
FROM AFWA...55 KT FROM SAB...AND 35 KT FROM TAFB.  A HIGH
RESOLUTION QUIKSCAT OVERPASS AT 1446Z SHOWED A 50 KT VECTOR NORTH
OF THE CENTER.  IN DEFERENCE TO THIS...THE INITIAL INTENSITY WILL
BE SET AT 50 KT...WITH THE CAVEAT THAT THIS COULD BE GENEROUS.

THE INITIAL MOTION IS 275/13.  DARBY REMAINS SOUTH OF A STRONG
LOW/MID LEVEL RIDGE...WHILE A MID/UPPER LEVEL TROUGH IS LOCATED
NORTH OF THE HAWAIIAN ISLANDS.  THE RIDGE SHOULD KEEP DARBY ON A
BASICALLY WESTWARD COURSE THROUGH 72 HR.  AFTER THAT...THE CYCLONE
COULD TURN MORE NORTHWARD IF IT STILL HAS ANY VERTICAL DEPTH.  THE
NOGAPS...WHICH KEEPS A DARBY STRONG THROUGH THE FORECAST
PERIOD...NOW CALLS FOR LESS OF A NORTHWARD TURN THAN EARLIER. 
OTHER LARGE-SCALE MODELS...WHICH FORECAST A WEAKER SYSTEM...
CONTINUE SHOW A MORE WESTERLY MOTION.  THE OFFICIAL FORECAST CALLS
FOR A WESTWARD TRACK FOR 72 HR...FOLLOWED BY A WEST-NORTHWESTWARD
MOTION.  THE TRACK IS NUDGED A LITTLE SOUTH OF THE PREVIOUS
PACKAGE...PARTICULARLY AT 96 AND 120 HR...AND IS IN BEST AGREEMENT
WITH THE CONSENSUS CONU GUIDANCE.  THE TRACK COULD BE SHIFTED MORE
SOUTHWARD IF DARBY WEAKENS FASTER THAN CURRENTLY FORECAST.

DARBY IS CURRENTLY OVER 24C SEA SURFACE TEMPERATURES.  WHILE THE
FORECAST TRACK CARRIES THE SYSTEM OVER INCREASING SSTS AFTER 24
HR...LARGE-SCALE MODELS INDICATE SIGNIFICANT WESTERLY VERTICAL
SHEAR SHOULD AFFECT DARBY AROUND THAT TIME.  THIS WILL LIKELY
PREVENT ANY RE-INTENSIFICATION AND MAKE IT DIFFICULT FOR DARBY TO
MAINTAIN ITSELF AS A TROPICAL CYCLONE.  THE INTENSITY FORECAST HAS
BEEN CHANGED TO CALL FOR DARBY TO BE DISSIPATING BY 72 HR AND A
NON-CONVECTIVE REMNANT LOW THEREAFTER.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/2100Z 18.7N 133.7W    50 KT
 12HR VT     31/0600Z 18.9N 135.7W    40 KT
 24HR VT     31/1800Z 19.1N 138.4W    30 KT
 36HR VT     01/0600Z 19.2N 141.3W    25 KT
 48HR VT     01/1800Z 19.3N 144.3W    25 KT
 72HR VT     02/1800Z 19.5N 149.5W    25 KT...DISSIPATING
 96HR VT     03/1800Z 20.5N 153.5W    20 KT...REMNANT LOW
120HR VT     04/1800Z 21.5N 156.5W    20 KT...REMNANT LOW
 
 
$$
NNNN


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Page last modified: Friday, 30-Jul-2004 20:42:28 UTC