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Tropical Storm MARTY


ZCZC MIATCDEP3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM MARTY DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT FRI SEP 19 2003
 
EARLIER QUIKSCAT AND SSMI MICROWAVE SATELLITE DATA...ALONG WITH THE
FIRST COUPLE OF VISIBLE IMAGES...SUGGEST THAT THE CENTER OF MARTY
IS A LITTLE FARTHER EAST OF THE PREVIOUS ADVISORY POSITION. THIS
PLACES THE LOW-LEVEL CENTER NEAR THE EASTERN EDGE OF THE NOW
WEAKENING CENTRAL DEEP CONVECTION. THE INITIAL INTENSITY OF 40 KT
IS BASED ON A COMBINATION OF A SATELLITE INTENSITY ESTIMATE OF
T2.5...OR 35 KT...FROM TAFB AND SAB...AND A DATA T-NUMBER OF T3.0
...OR 45 KT...FROM TAFB.

THE INITIAL MOTION ESTIMATE IS 300/6.  THERE IS A LITTLE LESS
UNCERTAINTY IN THE LOCATION OF THE CENTER NOW...SO THE PAST
HISTORICAL TRACK HAS BEEN ADJUSTED TO THE EAST AND SLOWER. THIS HAS
HAD A SIGNIFICANT IMPACT ON THE NHC MODEL GUIDANCE FORECAST TRACKS
FOR THIS ADVISORY PACKAGE. THE GFDL...GFS ENSEMBLE...AND UKMET
MODELS ARE NOW INDICATING RECURVATURE TO THE NORTH AND NORTHEAST
THROUGH A WEAKENING SUBTROPICAL RIDGE LOCATED ACROSS NORTHWESTERN
MEXICO AND EXTENDING WESTWARD ACROSS BAJA CALIFORNIA. THE GFS MODEL
DOES NOT WEAKEN THE RIDGE AS MUCH AS THE OTHER THREE MODELS DO...
WHILE THE NOGAPS MODEL FORECASTS MARTY TO BE A VERY WEAK SYSTEM
THAT IS DRIVEN RAPIDLY WESTWARD BY THE MODERATE LOW-LEVEL
EASTERLIES. IT APPEARS THAT NOGAPS IS KEEPING MARTY TOO WEAK...SO
THE WESTWARD TRACK HAS BEEN DISCOUNTED AT THIS TIME. LESS WEIGHT
HAS ALSO BEEN PLACED ON THE RECURVATURE FORECAST OF THE OTHER
MODELS...EXCLUDING THE GFS. THE CURRENT STRENGTH OF THE SUBTROPICAL
RIDGE AND THE RATHER WEAK LOOKING SHORTWAVE TROUGH FORECAST TO DIG
SOUTHEASTWARD FROM THE CENTRAL PACIFIC MAY NOT BE STRONG ENOUGH TO
COMPLETELY CAPTURE MARTY. HOWEVER...THE OFFICIAL FORECAST TRACK WAS
SHIFTED WELL TO THE RIGHT...ESPECIALLY AFTER 72 HOURS...DUE TO THE
REPOSITIONING OF THE CYCLONE CENTER AND ALSO TO BRING THE FORECAST
TRACK CLOSER TO THE GFS SOLUTION AND THE NHC MODEL CONSENSUS.
RECURVATURE ACROSS BAJA CALIFORNIA AFTER 72 HOURS IS A
LOW-PROBABILITY ALTERNATE SCENARIO AT THIS TIME...BUT IT WILL GIVEN
MORE CONSIDERATION IN THE NEXT ADVISORY IF MORE OF THE 12Z MODELS
BEGIN TO SUGGEST A NORTH AND NORTHEASTWARD MOTION BY 72 HOURS.
 
MARTY IS FORECAST TO REMAIN OVER 29-30C SSTS AND IN A LOW-SHEAR...
LESS THAN 5 KT...UPPER-LEVEL ENVIRONMENT...WHICH WOULD TEND TO FAVOR
A RAPID INTENSIFICATION TREND. HOWEVER...DUE TO THE UNCERTAINTY IN
THE EXACT LOCATION OF THE LOW-LEVEL CENTER WITHIN THE CENTRAL DEEP
CONVECTION...AND THE FACT THAT SOME MID-LEVEL EASTERLIES AND DRY
AIR IS UNDERCUTTING THE IMPRESSIVE OUTFLOW PATTERN...ONLY MODEST
INTENSIFICATION IS FORECAST. THE INTENSITY FORECAST IS SIMILAR TO
BUT SLIGHTLY FASTER THAN THE GFDL AND SHIPS INTENSITY MODEL
FORECASTS. HOWEVER...IF THE CENTER BECOMES EMBEDDED IN THE DEEP
CONVECTION LATER TODAY AND THE CONVECTION INCREASES SIGNIFICANTLY
...THEN MARTY COULD INTENSIFY MORE QUICKLY THAN THE CURRENT
FORECAST IS INDICATING.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/1500Z 17.4N 107.5W    40 KT
 12HR VT     20/0000Z 17.9N 108.3W    45 KT
 24HR VT     20/1200Z 18.4N 109.7W    55 KT
 36HR VT     21/0000Z 19.0N 111.3W    65 KT
 48HR VT     21/1200Z 19.5N 112.8W    75 KT
 72HR VT     22/1200Z 20.5N 115.5W    80 KT
 96HR VT     23/1200Z 21.5N 118.0W    75 KT
120HR VT     24/1200Z 23.5N 121.0W    65 KT
 
 
NNNN


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Page last modified: Monday, 07-Feb-2005 16:49:59 UTC