Tropical Storm TWELVE Advisory Sat Sep 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (TWELVE)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 12W (TWELVE), LOCATED APPROXIMATELY 275
NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-
NORTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED
ENHANCED INFRARED SATELLITE IMAGERY INDICATES DEEP CONVECTIVE
ACTIVITY HAS INCREASED OVER THE PAST SIX HOURS AND BECOME MORE
SYMMETRIC. ADDITIONALLY, AS THE CENTRAL DENSE OVERCAST HAS EXPANDED,
THE LOW LEVEL CIRCULATION CENTER (LLCC) IS NO LONGER FULLY EXPOSED.
A 111837Z SSMI 85 GHZ PASS DEPICTS THE GENERALLY WEAK LLCC STRUCTURE
THAT IS DISPLACED APPROXIMATELY 50 NM SW OF THE STRONG CONVERGENT
FLOW PRODUCING THE DEEP CONVECTION TO THE NORTHEAST. THE INITIAL
POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON A BLEND OF AGENCY
FIXES AND THE AFOREMENTIONED SSMIS DATA. THE INITIAL INTENSITY IS
ASSESSED AT 25 KNOTS, BASED ON AGENCY DVORAK FIXES RANGING FROM T1.0
TO T1.5 (25 KNOTS). THIS INTENSITY IS REPRESENTATIVE OF THE OVERALL
SURFACE CHARACTERISTICS OBSERVED IN 111030Z ASCAT-A DATA, WHILE
ISOLATED HIGHER WINDS LIKELY EXIST UNDER THE DEEP CONVECTION.
OUTFLOW IS CURRENTLY BEING ENHANCED AS IT TAPS INTO THE MIDLATITUDE
FLOW TO THE NORTH, HOWEVER, HIGH (20 KNOT) SOUTHWESTERLY VERTICAL
WIND SHEAR IS LIMITING THE POTENTIAL FOR SIGNIFICANT DEVELOPMENT.
SEA SURFACE TEMPERATURES REMAIN FAVORABLE AT 28 DEGREES C. THE FSU
PHASE SPACE PRODUCT INDICATES 12W IS ON THE BORDER BETWEEN SYMMETRIC
WARM AND COLD CORE STRUCTURE AS IT TRACKS AROUND THE WESTERN
PERIPHERY OF A SUB-TROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD TWELVE IS FORECAST TO CONTINUE TO ROUNDING THE STR OVER,
AND BECOME FULLY EXTRATROPICAL BY TAU 36 AS IT INTERACTS WITH THE
MID-LATITUDE FLOW. THIS ASSESSMENT IS CONSISTENT WITH THE FSU PHASE
SPACE. ADDITIONAL INTENSIFICATION SHOULD REMAIN LIMITED DUE TO THE
HIGH VWS, ALTHOUGH THE FORECAST INTENSITY IS INCREASED MODESTLY TO
30 KNOTS TO ACCOUNT FOR THE LLCC BECOMING MORE ALIGNED WITH THE
CONVECTION. LIMITED INITIAL MODEL GUIDANCE INDICATES STATISTICAL
GUIDANCE FAVORS THE FLAT INTENSIFICATION TREND, WHILE THE HWRF MODEL
SUGGESTS INTENSIFICATION TO TROPICAL STORM STATUS IS A POSSIBILITY.
MODEL TRACKS HOWEVER ARE IN GOOD AGREEMENT WITH THE FORECAST
RECURVATURE SCENARIO. AS THIS IS THE INITIAL FORECAST WITH LIMITED
AVAILABLE GUIDANCE, THE JTWC FORECAST CONFIDENCE IS ASSESSED AS
LOW.//
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