Tropical Storm ATSANI Advisory 10月29日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ASTANI), LOCATED APPROXIMATELY 389 NM
SOUTH-SOUTHEAST OF ANDERSEN AFB, HAS TRACKED NORTHWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS AND RELATIVELY DISORGANIZED SYSTEM, WITH DEEP
CONVECTION FLARING TO THE EAST OF THE BROAD LOW LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH MODERATE
CONFIDENCE BASED ON A COMBINATION OF ANIMATED 3.9 MICRON SHORTWAVE
INFRARED IMAGERY, SUPPORTED BY A 291155Z ASCAT-B BULLSEYE THAT
SHOWED THE DISORGANIZED AND ASYMMETRIC CIRCULATION TO GOOD EFFECT.
THE INITIAL INTENSITY IS ASSESSED WITH MODERATE CONFIDENCE BASED ON
DVORAK CURRENT INTENSITY ESTIMATES OF T1.5 (25 KNOTS) FROM BOTH PGTW
AND KNES. THE AFOREMENTIONED ASCAT DATA DID INDICATE 30 KNOT WINDS
WITH SOME ISOLATED 35 KNOT WINDS IN THE SOUTHEAST QUADRANT, HOWEVER
THESE HIGHER WINDS ARE ALL CONFINED TO THE SOUTHERN SIDE OF THE
SYSTEM, WITH ONLY 15-20 KNOT MAXIMUM WINDS ON THE NORTHERN SIDE. DUE
TO THIS ASYMMETRY, THE INITIAL INTENSITY WAS SET AT 25 KNOTS. TD 23W
IS TRACKING JUST A BIT WEST OF DUE NORTH UNDER THE STEERING
INFLUENCE OF AN EXTENSION OF A LARGE, DEEP-LAYER SUBTROPICAL RIDGE
(STR) CENTERED FAR TO THE NORTHEAST. TD 23W IS TRACKING THROUGH A
GENERALLY FAVORABLE ENVIRONMENT WITH WARM (30 DEG CELSIUS) SSTS,
GOOD WESTWARD AND EQUATORWARD OUTFLOW OFFSETTING MODERATE TO HIGH
(20-25 KNOTS) VWS.
3. FORECAST REASONING.
   A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE
FORECAST PHILOSOPHY.
   B. TD 2W IS FORECAST TO TURN TO A MORE NORTHWESTWARD TRACK OVER
THE NEXT 12 HOURS, AS THE STEERING RIDGE REORIENTS SLIGHTLY, AND TO
CONTINUE THIS NORTHWESTWARD TRACK THROUGH TAU 72. AS THE SYSTEM
TRACKS NORTHWESTWARD, IT WILL BEGIN TO BE IMPACTED BY THE OUTFLOW
FROM TY 22W, WITH CONVERGENT UPPER-LEVEL FLOW MOVING DOWN FROM THE
NORTH LIMITING THE AVAILABLE OUTFLOW TO A SINGLE WESTWARD CHANNEL.
THIS, COMBINED WITH MODERATE VWS WILL OFFSET THE VERY WARM (30 DEG
CELSIUS), HIGH OHC WATERS OVER WHICH THE SYSTEM WILL TRACK. BY TAU
48 THE UPPER-LEVEL PATTERN WILL BEGIN TO SHIFT, WITH THE FORECAST
DEVELOPMENT OF AN UPPER-LEVEL ANTICYCLONE JUST EAST OF THE LLCC,
PROVIDING INCREASING DIVERGENT OUTFLOW, AND ALLOWING THE SYSTEM TO
START INTENSIFYING AT A FASTER RATE, INCREASING TO 80 KNOTS BY TAU
72. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 36 BUT
CROSS-TRACK SPREAD INCREASES TO 185 NM AT TAU 72  WITH JGSM AND GFS
REPRESENTING THE NORTH AND SOUTH OUTLIERS AT TAU 72. THE JTWC
FORECAST TRACK LIES ALONG THE NORTHERN EDGE OF THE MODEL ENVELOPE
THROUGH TAU 12 TO REFLECT THE NEAR-TERM MOTION, THEN LIES VERY CLOSE
TO THE MULTI-MODEL CONSENSUS THOUGH TAU 72 WITH FAIR CONFIDENCE.
   C. BEYOND TAU 72, THE SYSTEM WILL SLOW DOWN WHILE TURNING MORE
NORTHWARD TOWARDS A WEAKNESS A COL AREA THAT DEVELOPS IN A WEAKNESS
IN THE STR TO THE NORTH. AS THE SYSTEM CLOSER TO THE COL REGION, IT
BEGINS TO TAP INTO DUAL-CHANNEL OUTFLOW, ALLOWING IT TO QUICKLY
INTENSIFY FROM TAU 72 TO TAU 96, PEAKING AT 100 KNOTS. THEREAFTER
INTENSITY REMAINS STEADY AS THE SYSTEM MOVES SLOWLY ACROSS AN AREA
OF COOLER WATERS IN THE WAKE OF TY 22W, WHILE OUTFLOW DEGRADES
SIMULTANEOUSLY. NUMERICAL GUIDANCE IS MIXED BEYOND TAU 72, WITH A
BIFURCATION SCENARIO SETTING UP AFTER TAU 96. THE GFS SOLUTION
INCREASES THE STRENGTH OF THE STEERING RIDGE TO THE NORTH AND TRACKS
THE SYSTEM ON A MORE WESTWARD TRACK TOWARDS THE BASHI CHANNEL BEYOND
TAU 120. THE ECMWF AND NAVGEM FAVOR A SLOW TRACK NORTHWARD INTO A
STRONG WEAKNESS IN THE STR, LEADING TO A 320 NM SPREAD AT TAU 120.
THE JTWC FORECAST TRACKS SLOWER AND JUST WEST OF THE MULTI-MODEL
CONSENSUS AND FAVORS THE ECMWF AND NAVGEM SOLUTIONS WITH LOW
CONFIDENCE.//
NNNN
NNNN