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Tropical Storm KRISTY Forecast Discussion Number 4

Issued at 200 AM PDT THU SEP 13 2012

000
WTPZ41 KNHC 130847
TCDEP1
 
TROPICAL STORM KRISTY DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP112012
200 AM PDT THU SEP 13 2012
 
A SERIES OF MICROWAVE OVERPASS DURING THE EARLY EVENING HAVE BEEN
VERY HELPFUL IN DETERMING THE INITIAL POSITION AND MOTION OF
KRISTY.  THE LATEST MICROWAVE IMAGE...A 0428 UTC AMSU PASS...
INDICATED SOME NORTHWEST TO SOUTHEAST TILT OF THE CIRCULATION...AND
RECENT INFRARED SATELLITE IMAGES SHOW A SHARPER NORTHWESTERN EDGE
OF THE DEEP CONVECTION.  THIS...ALONG WITH ANALYSES FROM THE SHIPS
MODEL AND CIMSS...SUGGESTS SOME NORTHWESTERLY SHEAR HAS STARTED
AFFECTING THE CYCLONE.  THE LATEST OBJECTIVE AND SUBJECTIVE
SATELLITE ESTIMATES STILL SUPPORT AN INITIAL INTENSITY OF 45 KT.  

KRISTY IS LOCATED TO THE EAST OF AN UPPER-LEVEL ANTICYCLONE AND THIS
IS FORECAST TO KEEP THE CYCLONE IN AN AREA OF LIGHT TO MODERATE
NORTHWESTERLY SHEAR DURING THE NEXT 12 HOURS OR SO.  AFTER
THAT...THE SHEAR SHOULD RELAX AND KRISTY WILL STILL BE OVER WARM
WATER AND IN A MOIST ENVIRONMENT.  THIS SHOULD ALLOW FOR A GRADUAL
INCREASE IN STRENGTH AND THE OFFICIAL FORECAST CALLS FOR A PEAK
INTENSITY NEAR HURRICANE STRENGTH IN ABOUT 36 HOURS.  IN A COUPLE
OF DAYS KRISTY WILL BE MOVING OVER COOLER WATERS AND STEADY
WEAKENING IS ANTICIPATE AFTER THAT TIME. 
 
THE TROPICAL STORM IS MOVING WEST-NORTHWESTWARD OR 295 DEGREES AT 9
KT.  KRISTY IS EXPECTED TO CONTINUE ON THIS GENERAL HEADING FOR THE
NEXT FEW DAYS AS IT IS STEERED BY A MID-LEVEL RIDGE TO THE
NORTHEAST OF THE CYCLONE.  THE TRACK GUIDANCE IS IN GOOD AGREEMENT
ON THIS SCENARIO...EXCEPT FOR THE GFDL MODEL WHICH REMAINS AN
OUTLIER AS IT SHOWS A TRACK TOWARD BAJA CALIFORNIA.  THE NHC 
TRACK FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND IS NEAR
THE CONSENSUS OF THE GFS...ECMWF...UKMET...AND HWRF MODELS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 18.5N 108.5W   45 KT  50 MPH
 12H  13/1800Z 19.0N 109.7W   50 KT  60 MPH
 24H  14/0600Z 19.6N 111.2W   55 KT  65 MPH
 36H  14/1800Z 20.5N 112.8W   60 KT  70 MPH
 48H  15/0600Z 21.7N 114.5W   55 KT  65 MPH
 72H  16/0600Z 23.9N 118.2W   40 KT  45 MPH
 96H  17/0600Z 25.0N 120.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  18/0600Z 25.5N 121.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BROWN
 

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