WDPN33 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (TORAJI) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 118.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 283 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A ASYMMETRIC
CIRCULATION WITH AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC)
AND FLARING CONVECTION MOSTLY CONFINED TO THE WESTERN AND NORTHERN
PERIPHERIES. A 120643Z GMI 37GHZ MICROWAVE IMAGE SHOWED AN
ELONGATED LOW EMISSIVITY REGION INDICATIVE OF THE IRREGULAR LLCC
SEEN IN THE MSI. COMPARED TO THE 89GHZ IMAGE, A MODERATE AMOUNT OF
SOUTHERLY SHEAR BECOMES EVIDENT, WITH THE UPPER-LEVEL CENTER
DISPLACED WELL TO THE NORTHEAST OF THE LLCC. CIMSS SHEAR IS ESTIMATED 
AT 10 KNOTS FROM THE SOUTHEAST, BUT BASED ON THE MICROWAVE IMAGERY,
IT IS LIKELY A BIT HIGHER AND FROM MORE OF A SOUTH TO SOUTHWEST
DIRECTION. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE MICROWAVE IMAGE NOTED ABOVE. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE, HEDGED A BIT HIGHER THAN THE BULK
OF THE AGENCY AND OBJECTIVE INTENSITY ESTIMATES NOTED ABOVE. THE
WIND FIELD IS STEADILY EXPANDING AS THE SYSTEM MOVES FURTHER INTO
THE SOUTH CHINA SEA, WITH PRATAS ISLAND, APPROXIMATELY 120NM TO THE
NORTHWEST OF THE 0600Z POSITION, NOW REPORTING 37 KNOT
NORTHEASTERLY SUSTAINED WINDS. THE ENVIRONMENT IS IN GENERAL
MARGINAL TO MARGINALLY FAVORABLE, WITH WARM SSTS, LOW TO MODERATE
SHEAR AND STRONG POLEWARD OUTFLOW. BUT THE RELATIVELY LARGE AND
IRREGULAR VORTEX HAS NOT RECOVERED FULLY FROM PASSAGE OVER LUZON
AND IS INGESTING SOME DRY MID-LEVEL AIR INTO THE EASTERN SIDE OF
THE CIRCULATION, WHICH IS INHIBITING DEVELOPMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA AND SURFACE
OBSERVATIONS.

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) SOUTHEAST OF OKINAWA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 35 KTS AT 120530Z
   CIMSS AIDT: 37 KTS AT 120530Z
   CIMSS D-MINT: 41 KTS AT 120643Z
   CIMSS D-PRINT: 39 KTS AT 120530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 26W WILL CONTINUE TO TRACK
TOWARDS THE NORTHWEST ALONG THE SOUTHWESTERN SIDE OF THE STEERING
RIDGE FOR THE NEXT 12 TO 24 HOURS, THOUGH THE STEERING GRADIENT
REMAINS RELATIVELY WEAK AND TRACK SPEEDS WILL CORRESPONDINGLY BE
LOW. AFTER TAU 24, THE STR TO THE NORTH BREAKS, RESULTING IN AN
EVEN WEAKER STEERING PATTERN. TS 24W BEGINS TO SLOW DOWN AT THIS
POINT WHILE TURNING TOWARDS THE WEST. FOR THE NEXT 24 HOURS, THE
ENVIRONMENT IS FORECAST TO REMAIN MARGINAL TO MARGINALLY FAVORABLE,
WITH STRONG POLEWARD OUTFLOW AND LOW VERTICAL WIND SHEAR, ALLOWING
FOR A BRIEF PERIOD OF MODEST INTENSIFICATION. BUT BY TAU 36, THE
PARTY WILL BE OVER. MID-LEVEL WESTERLY SHEAR WILL START TO PICK UP
AS EARLY AS TAU 24, KICKING OFF THE RAPID WEAKENING TREND. BY TAU
36, WESTERLY SHEAR IS FORECAST TO INCREASE TO 30 KNOTS OR HIGHER,
PARTICULARLY IN THE MID-LEVELS. ACCOMPANYING THIS INCREASE IN SHEAR
WILL BE A SURGE IN DRY AIR ABOVE ABOUT 700MB. RAPIDLY MOVING IN
FROM THE SOUTHWEST, THIS DRY AIR WILL COMPLETELY SMOTHER THE VORTEX BY 
TAU 48. WHATS LEFT OF THE VORTEX WILL RAPIDLY WEAKEN AS IT TURNS 
SOUTHWARD AFTER TAU 48, ALONG THE LOW-LEVEL FLOW LINES. THE SYSTEM IS 
EXPECTED TO FULLY DISSIPATE AS A TROPICAL CYCLONE NO LATER THAN TAU 
72, 
EAST OF HAINAN ISLAND. 

MODEL DISCUSSION: TRACK GUIDANCE IS FOR THE MOST PART IN AGREEMENT
ON THE OVERALL TRACK SCENARIO, WITH MODEST AMOUNTS OF SPREAD. THE
NAVGEM IS AN OUTLIER THROUGH THE ENTIRETY OF THE FORECAST PERIOD,
TAKING THE SYSTEM MUCH TOO FAR TO THE SOUTH AND HAS BEEN DISCARDED
FROM THE CONSENSUS. DISCARDING THE NAVGEM LEADS TO A TIGHTLY PACKED
GUIDANCE PACKAGE, WITH A 45NM SPREAD CENTERED ON THE JTWC FORECAST
TRACK AT TAU 48. AFTER THE SYSTEM IS DECAPITATED, WHERE THE MODELS
TAKE THE REMNANT VORTEX UNSURPRISINGLY BEGINS TO SPREAD OUT. BY TAU
72, CROSS-TRACK SPREAD INCREASES TO 150NM BETWEEN THE JGSM TO THE
NORTHWEST, NEAR HAINAN, AND THE UKMET ENSEMBLE MEAN, WHICH CURVES
THE SYSTEM BACK TO THE SOUTHEAST. THE JTWC FORECAST LIES CLOSE TO
BOTH THE CONSENSUS MEAN AND THE EMCWF DETERMINISTIC TRACKER THROUGH
THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS
IN VERY GOOD AGREEMENT THAT THE SYSTEM WILL INTENSIFY TO 50 KNOTS
BY TAU 12, STAGNATE THERE FOR 12 HOURS AND THEN RAPIDLY WEAKEN,
DISSIPATING NO LATER THAN TAU 72 AND POTENTIALLY AS EARLY AS TAU
60. THE JTWC FORECAST LIES SLIGHTLY ABOVE THE CONSENSUS MEAN WITH
MEDIUM CONFIDENCE.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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