Tropical Storm IGNACIO

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TROPICAL STORM IGNACIO DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122009
800 PM PDT MON AUG 24 2009
 
ALTHOUGH SOME OF THE DEEP CONVECTION WITHIN THE CURVED BAND TO THE
WEST OF THE CYCLONE CENTER HAS DIMINISHED...SATELLITE INTENSITY
ESTIMATES ARE NOW T3.0 FROM TAFB AND T2.5 FROM SAB. BASED ON
THIS...THE DEPRESSION IS BEING UPGRADED TO TROPICAL STORM IGNACIO.
THE LOW-LEVEL CENTER POSITION REMAINS A LITTLE UNCERTAIN...AND THE
POSITION GIVEN HERE IS LIKELY A MEAN POSITION OF SEVERAL SWIRLS
ROTATING AROUND A COMMON CENTER. A 2056 UTC AMSR-E PASS INDICATED
THAT THIS MEAN CENTER IS PROBABLY A LITTLE FARTHER NORTH THAN
PREVIOUSLY THOUGHT...AND THE NEW FORECAST TRACK HAS CONSEQUENTLY
BEEN SHIFTED A LITTLE TO THE NORTH THROUGH THE FIRST 72 HOURS. THE
INITIAL MOTION IS 290/09...BUT IGNACIO IS EXPECTED TO TURN TOWARD
THE NORTHWEST BY 36 HOURS AS IT BEGINS TO MOVE AROUND THE WESTERN
PERIPHERY OF A SUBTROPICAL RIDGE EXTENDING WEST OF NORTHERN MEXICO.
ONCE THE CYCLONE WEAKENS BY 96 AND 120 HOURS...IT IS EXPECTED TO
TURN BACK TOWARD THE WEST-NORTHWEST AS IT IS STEERED BY THE
LOW-LEVEL FLOW. THE TRACK GUIDANCE IS IN REASONABLY GOOD AGREEMENT
THROUGH 120 HOURS...AND VERY LITTLE CHANGE WAS MADE TO THE PREVIOUS
FORECAST.
 
IGNACIO WILL BE MOVING OVER WATER THAT IS AT LEAST 26 DEG CELSIUS
FOR ANOTHER 36 HOURS OR SO. VERTICAL SHEAR IS EXPECTED TO REMAIN
LIGHT...SO SOME STRENGTHENING IS ANTICIPATED UNTIL THE SEA SURFACE
TEMPERATURES BEGIN TO DECREASE. THE OFFICIAL FORECAST REMAINS AT
THE UPPER END OF THE INTENSITY GUIDANCE AND IS VERY CLOSE TO THE
SHIPS MODEL THROUGH 36 HOURS. WHILE THE DYNAMICAL GFDL AND HWRF
MODELS...AS WELL AS THE STATISTICAL LGEM...ONLY STRENGTHEN IGNACIO
TO ABOUT 40-45 KT...THE PEAK INTENSITY SHOWN IN THE FORECAST IS NOT
BEING LOWERED...SINCE ONLY A SLIGHT INCREASE IN ORGANIZATION WOULD
SUPPORT SATELLITE INTENSITY ESTIMATES OF 55 KT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/0300Z 17.0N 117.8W    35 KT
 12HR VT     25/1200Z 17.4N 119.1W    40 KT
 24HR VT     26/0000Z 18.1N 120.9W    50 KT
 36HR VT     26/1200Z 19.2N 122.6W    55 KT
 48HR VT     27/0000Z 20.8N 124.3W    50 KT
 72HR VT     28/0000Z 24.0N 127.5W    40 KT
 96HR VT     29/0000Z 26.5N 131.0W    25 KT...REMNANT LOW
120HR VT     30/0000Z 27.5N 134.5W    20 KT...REMNANT LOW
 
$$
FORECASTER BERG
 
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