Tropical Storm NORA

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TROPICAL STORM NORA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP172009
200 AM PDT THU SEP 24 2009
 
THE COVERAGE AND INTENSITY OF THE CENTRAL CONVECTION ASSOCIATED
WITH NORA DECREASED IN THE HOURS PRIOR TO THE GOES-WEST ECLIPSE
PERIOD. THIS LIKELY OCCURRED DUE TO INCREASING SOUTHWESTERLY WIND
SHEAR ANALYZED BY UW-CIMSS AND THE SHIPS MODEL...ALONG WITH A
DRYING TREND IN THE MID-TROPOSPHERE AND A DECREASE IN UPPER-LEVEL
DIVERGENCE INDICATED BY SHIPS. SUBJECTIVE AND OBJECTIVE FINAL-T
NUMBERS WERE A UNANIMOUS 3.0 AT 0600 UTC...AND ON THIS BASIS THE
INITIAL INTENSITY IS LOWERED TO 45 KT.
 
THE INTENSITY GUIDANCE IS IN UNANIMOUS AGREEMENT THAT NORA HAS
PEAKED. THE SHIPS MODEL FORECASTS AT LEAST 15-20 KT OF SHEAR
THROUGH THE PERIOD...WHICH IN COMBINATION WITH THE MARGINAL
ATMOSPHERIC ENVIRONMENT SHOULD RESULT IN SLOW WEAKENING. THE
INTENSITY FORECAST HAS BEEN ADJUSTED DOWNWARD IN CLOSE AGREEMENT
WITH THE ICON INTENSITY CONSENSUS. NORA SHOULD BECOME A REMNANT LOW
IN ABOUT 4 DAYS AND BE DISSIPATING BY DAY 5.
 
BASED ON SEVERAL MICROWAVE FIXES AND GEOSTATIONARY IMAGERY PRIOR TO
THE ECLIPSE...NORA APPEARS TO HAVE BEEN MOVING VERY LITTLE OVER THE
PAST FEW HOURS. A 12-HOUR INITIAL MOTION ESTIMATE OF 300/04 WAS
USED FOR THIS ADVISORY. THE TRACK MODEL GUIDANCE IS IN REASONABLY
GOOD AGREEMENT ON THE OVERALL FORECAST SCENARIO. AS NORA WEAKENS...
THE CYCLONE WILL TURN WESTWARD TO THE SOUTH OF THE LOW-LEVEL RIDGE
THROUGH ABOUT 72 HOURS. BEYOND THAT TIME...MOST OF THE GUIDANCE
SHOWS A TURN TOWARD THE WEST-NORTHWEST IN 3 OR 4 DAYS AS THE
LOW-LEVEL RIDGE WEAKENS...ALLOWING WHAT IS LEFT OF NORA TO GAIN
SOME LATITUDE. THE OFFICIAL FORECAST IS ADJUSTED SLIGHTLY NORTH
THROUGH 24 HOURS TO ACCOUNT FOR THE INITIAL MOTION...AND THEN IS
SIMILAR TO THE PREVIOUS PACKAGE THROUGH 72 HOURS. AT DAYS 4 AND 5
THE FORECAST IS SHIFTED SLIGHTLY SOUTHWARD TOWARD THE TVCN
MULTI-MODEL CONSENSUS AND LIES NEAR THE MIDDLE OF THE GUIDANCE
ENVELOPE.
 
THE INITIAL 34-KT WIND RADII WERE ADJUSTED BASED ON A QUIKSCAT PASS
AT 0150 UTC.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/0900Z 17.2N 119.2W    45 KT
 12HR VT     24/1800Z 17.4N 120.0W    45 KT
 24HR VT     25/0600Z 17.5N 121.2W    40 KT
 36HR VT     25/1800Z 17.3N 122.5W    35 KT
 48HR VT     26/0600Z 17.3N 124.0W    30 KT
 72HR VT     27/0600Z 18.0N 127.0W    25 KT
 96HR VT     28/0600Z 19.0N 129.5W    25 KT...REMNANT LOW
120HR VT     29/0600Z 19.6N 131.5W    20 KT...DISSIPATING
 
$$
FORECASTER BRENNAN
 
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