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Tropical Storm NORA


ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM NORA DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP172009
800 AM PDT WED SEP 23 2009

NORA HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING...AS A
CENTRAL CONVECTIVE FEATURE HAS FORMED WITH AN OUTER BAND IN THE
WESTERN SEMICIRCLE.  SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM
TAFB AND 35 KT FROM SAB...AND BASED ON THIS THE INITIAL INTENSITY
IS INCREASED TO 40 KT.  THE CIRRUS OUTFLOW IS CURRENTLY FAIR TO
GOOD IN ALL DIRECTIONS.

THE INITIAL MOTION IS 300/8...A LITTLE TO THE LEFT AND SLIGHTLY
FASTER THAN PREVIOUSLY.  NORA IS ON THE SOUTH SIDE OF A LOW-LEVEL
RIDGE...AND ALSO SOUTH OF A WEAKNESS IN THE MID-LEVEL RIDGE.  THE
LARGE-SCALE MODELS FORECAST THE LOW-LEVEL RIDGE TO REMAIN IN PLACE
FOR THE NEXT SEVERAL DAYS WHILE A MID/UPPER-LEVEL LOW FORMS TO THE
NORTHWEST OF NORA.  THIS EVOLUTION SHOULD STEER NORA GENERALLY
WEST-NORTHWESTWARD OR WESTWARD FOR THE NEXT 24-36 HR.  THE MOTION
BEYOND THAT TIME DEPENDS ON HOW STRONG NORA GETS.  A STRONGER AND
VERTICALLY DEEPER SYSTEM SHOULD TURN MORE TOWARD THE NORTHWEST AS
FORECAST BY THE GFDL...HWRF...AND CANADIAN MODELS.  A WEAKER AND
SHALLOWER NORA SHOULD MOVE MORE WESTWARD AS FORECAST BY THE
BAMS...GFS...AND ECMWF.  THE TRACK FORECAST WILL LEAN TOWARD THE
LATTER SCENARIO...WITH A SLOW AND GENERALLY WESTWARD MOTION AFTER
36 HR.

NORA IS CURRENTLY IN AN ENVIRONMENT OF LIGHT SOUTHERLY VERTICAL WIND
SHEAR.  THE LARGE-SCALE MODELS SUGGEST THAT THE CYCLONE WILL REMAIN
IN A FAVORABLE ENVIRONMENT FOR ABOUT 24 HR MORE...FOLLOWED BY A
SIGNIFICANT INCREASE IN THE SHEAR AS NORA REACHES COOLER SEA
SURFACE TEMPERATURES.  THIS SUGGESTS THAT NORA SHOULD STRENGTHEN
FOR A DAY OR SO...FOLLOWED BY A STEADY WEAKENING.  THE NEW
INTENSITY FORECAST FOLLOWS THE SHIPS AND LGEM GUIDANCE...CALLING
FOR A PEAK INTENSITY OF 55 KT IN 24 HR AND WEAKENING TO A REMNANT
LOW BY 72 HR.  THE SHIPS RAPID INTENSIFICATION INDEX SHOWS A
25 PERCENT CHANCE OF A 30 KT INCREASE IN STRENGTH DURING THE NEXT
24 HR...SO IT CANNOT BE RULED OUT THAT NORA COULD BECOME A HURRICANE
BEFORE ENCOUNTERING THE STRONGER SHEAR.  THE GFDL AND HWRF SUPPORT
THIS POSSIBILITY BY FORECASTING NORA TO BECOME A HURRICANE. 
HOWEVER...THIS OCCURS IN BOTH MODELS ONLY AFTER THE STRONGER SHEAR
DEVELOPS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      23/1500Z 16.5N 117.5W    40 KT
 12HR VT     24/0000Z 16.9N 118.4W    50 KT
 24HR VT     24/1200Z 17.1N 119.4W    55 KT
 36HR VT     25/0000Z 17.2N 120.4W    50 KT
 48HR VT     25/1200Z 17.3N 121.4W    40 KT
 72HR VT     26/1200Z 17.5N 123.5W    25 KT...REMNANT LOW
 96HR VT     27/1200Z 18.0N 126.0W    20 KT...REMNANT LOW
120HR VT     28/1200Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
NNNN


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Page last modified: Thursday, 31-Dec-2009 12:09:28 UTC