000
WTPZ42 KNHC 241442
TCDEP2
TROPICAL STORM NORA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP172009
800 AM PDT THU SEP 24 2009
 
NORA IS BEGINNING TO BE AFFECTED BY WESTERLY VERTICAL WIND SHEAR.
RECENT TRMM DATA INDICATED THAT THE LOW-LEVEL CENTER WAS NEAR THE
WESTERN EDGE OF THE CONVECTIVE MASS...WHICH HAS INCREASED OVER THE
LAST FEW HOURS. IN ADDITION...ANALYSES FROM CIMSS AT THE UNIVERSITY
OF WISCONSIN SHOW 10-15 KT OF WEST-SOUTHWESTERLY SHEAR.  USING A
BLEND OF SATELLITE INTENSITY ESTIMATES...THE INITIAL INTENSITY IS
HELD AT 45 KT. 

NORA HAS LIKELY PEAKED IN INTENSITY...AS THE CYCLONE SHOULD
ENCOUNTER INCREASING WESTERLY SHEAR DUE TO AN UPPER-LEVEL TROUGH TO
ITS NORTHWEST.  STATISTICAL AND DYNAMICAL MODEL GUIDANCE IS IN
AGREEMENT IN SHOWING STEADY WEAKENING DUE TO THE SHEAR AND COOLER
WATERS ALONG THE FORECAST TRACK.  THE INTENSITY FORECAST HAS BEEN
ADJUSTED DOWNWARD BASED ON THESE FACTORS...TO A TROPICAL DEPRESSION
IN 36 HOURS AND TO A REMNANT LOW IN A FEW DAYS.

MICROWAVE FIXES HAVE HELPED LOCATE THE CENTER...RESULTING IN A MORE
CONFIDENT INITIAL MOTION OF 290/4. THE STRONG SHEAR WILL LIKELY
DECOUPLE THE CIRCULATION...WITH THE LOW-LEVEL CENTER TURNING MORE
TOWARD THE WEST OR WEST-SOUTHWEST OVER THE NEXT COUPLE OF DAYS AS
SHOWN BY MOST OF THE DYNAMICAL MODELS.  THEREAFTER...THE REMNANTS
OF NORA IS FORECAST TO TURN WEST-NORTHWEST WITH A REDUCTION IN
FORWARD SPEED DUE TO A BREAK IN THE SUBTROPICAL RIDGE. THIS
FORECAST IS SIMILAR TO BUT SLIGHTLY SOUTH OF THE PREVIOUS
FORECAST...TRENDING TOWARD THE MODEL CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/1500Z 17.3N 120.0W    45 KT
 12HR VT     25/0000Z 17.4N 120.9W    40 KT
 24HR VT     25/1200Z 17.2N 122.4W    35 KT
 36HR VT     26/0000Z 17.1N 123.6W    30 KT
 48HR VT     26/1200Z 17.2N 125.1W    25 KT
 72HR VT     27/1200Z 18.0N 128.0W    20 KT...REMNANT LOW
 96HR VT     28/1200Z 18.5N 130.5W    20 KT...REMNANT LOW
120HR VT     29/1200Z 19.0N 132.5W    20 KT...REMNANT LOW
 
$$
FORECASTER CANGIALOSI/BEVEN