WDXS31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (IGGY) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8S 108.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 605 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT SYSTEM WITH AN ELONGATED CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). THE CDO HAS BEEN
ABLE TO PERSIST OVER THE LAST SIX HOURS, THOUGH THE CONVECTION HAS
WARMED FAIRLY SIGNIFICANTLY. CYCLONIC ROTATION IS EVIDENT IN THE
EIR LOOP, SUGGESTIVE OF A POSSIBLE CIRCULATION CENTER, FAIRLY
ALIGNED VERTICALLY WITH THE LLCC. A 011146Z SSMIS MICROWAVE PASS
TELLS A DIFFERENT STORY HOWEVER, WITH THE 91GHZ IMAGE DEPICTED A
WEAK MICROWAVE EYE FEATURE WITH CYCLONICALLY CURVED CONVECTION
ACROSS THE NORTHERN PORTION OF THE CENTER. BY ITSELF THIS WOULD BE
FAIRLY CONCLUSIVE, BUT WHEN THE 37GHZ IMAGE LOOKS NOTHING LIKE THE
91GHZ IMAGE AND SUGGESTS A LLCC FURTHER NORTH, WHILE NEITHER LINES
UP WELL WITH THE EIR LOOP. MODEL CROSS-SECTIONS GENERALLY SUPPORT
THE FACT THAT THE VORTEX REMAINS SOMEWHAT TILTED, SOUTHWARD WITH
HEIGHT, WHICH IS ALSO SUPPORTED BY THE CIMSS SHEAR ESTIMATE OF
ABOUT 10 KNOTS OF SHEAR FROM THE NORTH. WITH THESE UNCERTAINTIES
AND CONFLICTING INFORMATION IN MIND, THE INITIAL POSITION IS
ASSESSED WITH LOW CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON AN AVERAGE OF THE AVAILABLE
OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED BELOW.
ENVIRONMENTAL CONDITIONS ARE GENERALLY FAVORABLE, WITH LOW VWS,
DECENT POLEWARD OUTFLOW AND WARM SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR EQUATORIAL RIDGE (NER) CENTERED OVER BORNEO. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS SATCON: 43 KTS AT 010910Z
   CIMSS ADT: 47 KTS AT 011210Z
   CIMSS AIDT: 39 KTS AT 011210Z
   CIMSS D-MINT: 40 KTS AT 010816Z
   CIMSS D-PRINT: 44 KTS AT 011210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: INDEPENDENT OF THE UNCERTAINTY SURROUNDING THE
INITIAL POSITION, TC 11S HAS CONTINUED ON A GENERAL SOUTHEASTWARD
TRACK OVER THE PAST SIX HOURS, THE ONLY QUESTION BEING HOW QUICKLY
HAS IT MOVED DOWN THE TRACK. THE PRIMARY DRIVER OF THE TRACK
CURRENTLY IS THE NER OVER SOUTHWESTERN BORNEO. TC 11S WILL RAPIDLY
DECELERATE AFTER TAU 12 AS THE NER SHIFTS WESTWARD AND A
SUBTROPICAL RIDGE (STR) BEGINS TO BUILD EASTWARD TOWARDS LEARMONTH.
TRACK SPEEDS REMAIN SLOW (03 KNOTS OR LESS) BETWEEN TAU 24 AND 36,
AS THE SYSTEM REACHES AND INFLECTION POINT AND TURNS SHARPLY
WEST-SOUTHWESTWARD AFTER TAU 24. NEAR-TERM INTENSITY CHANGES WILL
PRIMARILY BE DRIVEN BY TWO FACTORS. FIRST, THE VORTEX NEEDS TO
ALIGN BEFORE THE SYSTEM CAN INTENSIFY MUCH BEYOND ITS CURRENT
LEVEL. THE MODEL GUIDANCE SUPPORTS THIS OCCURRING WITHIN THE NEXT
12 HOURS UNDER CONTINUING FAVORABLE SHEAR CONDITIONS. THE SECOND
FACTOR WILL BE THE APPROACH OF AN UPPER-LEVEL TROF, WHICH IS
EXPECTED TO PASS BY TO THE SOUTH OVER THE NEXT 24 HOURS, PROVIDING
THE SYSTEM WILL SOME ENHANCED POLEWARD OUTFLOW. HOWEVER, THE DELAY
IN VORTEX ALIGNMENT MEANS THE WINDOW OF OPPORTUNITY IS FLEETING, 24
HOURS AT BEST. BEGINNING AT TAU 24, THE TROF PASSES TO THE EAST OF
TC 11S, AND WILL INTRODUCE A DRAMATIC INCREASE IN WESTERLY SHEAR
AND DRY AIR INTRUSION. THE VORTEX WILL RAPIDLY DECOUPLE DUE TO THE
SHEAR AND DRY MID-LEVEL AIR AND BEGIN TO WEAKEN. AS THE VORTEX
SHALLOWS, THE SYSTEM WILL COME UNDER THE STEERING INFLUENCE OF THE
LOW- TO MID-LEVELS OF THE STR TO THE SOUTH AND TRACK SOUTHWESTWARD
THROUGH THE REMAINDER OF THE FORECAST PERIOD. TC 11S IS FORECAST TO
DISSIPATE AS A TROPICAL CYCLONE NO LATER THAN TAU 72 AND LIKELY AS
EARLY AS TAU 60.   

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL
INTELLIGENCE (AI) MODELS REMAIN IN OVERALL AGREEMENT ON THE TRACK
SCENARIO. ALL AVAILABLE GUIDANCE SUPPORTS THE SLOWING SOUTHEASTWARD
TRACK THROUGH TAU 24, AND THE SYSTEM REACHING AN INFLECTION POINT
BY TAU 24. SIMILAR TO THE LAST MODEL RUN, THE GFS IS SITUATED ON
THE EASTERN EDGE OF THE TRACK ENVELOPE, AND ECMWF ON THE WEST, WITH
A 115NM SPREAD AT TAU 24. ALL MODELS TURN THE SYSTEM SHARPLY
WEST-SOUTHWESTWARD AFTER TAU 24, THEN ACCELERATE THE SYSTEM
SOUTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD.
CROSS-TRACK SPEAD REMAINS 100NM OR LESS THROUGH TAU 72, THOUGH
ALONG-TRACK SPREAD INCREASES TO 300NM BY THE END OF THE FORECAST,
BETWEEN THE FAST ECMWF AND SLOW GFS. THE JTWC FORECAST IS
POSITIONED NEAR THE AI MODEL CONSENSUS AND THE MULTI-MODEL
CONSENSUS MEAN WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN
GOOD AGREEMENT, THOUGH THE PEAK INTENSITY HAS COME DOWN OVERALL AS
COMPARED TO THE PREVIOUS RUN. THE HWRF IS THE SOLE OUTLIER
INDICATING A PEAK INTENSITY ABOVE 50 KNOTS, PEAKING AT ABOUT 57
KNOTS, WHILE ALL OF THE OTHER CONSENSUS MEMBERS ARE TIGHTLY PACKED
AROUND A 45-50 KNOT PEAK AT TAU 12 TO 24 FOLLOWED BY A STEADY
WEAKENING TREND THROUGH THE END OF THE FORECAST. THE JTWC FORECAST
IS PLACED NEAR THE HWRF THROUGH TAU 24, THEN JOINS THE MEAN THROUGH
THE REMAINDER OF THE FORECAST, WITH MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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