WDXS31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (EMNATI) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9S 57.1E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 239 NM NORTH-NORTHEAST OF ST DENIS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 13S HAS INTENSIFIED 20 KNOTS OVER THE PAST 24 HOURS FROM 65
KNOTS AT 181800Z TO THE INITIAL INTENSITY OF 85 KNOTS. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS A 10NM RAGGED EYE
WITH SPIRAL BANDING OVER THE NORTHERN SEMICIRCLE. A 191448Z SSMIS
91GHZ MICROWAVE IMAGE DEPICTS A SMALL MICROWAVE EYE FEATURE AND
SURROUNDING EYEWALL WITH A BREAK IN THE EYEWALL OVER THE EASTERN
QUADRANT. DEEP CONVECTIVE BANDING IS PRIMARILY LOCATED OVER THE
NORTHERN SEMICIRCLE WITH LIMITED BANDING OVER THE SOUTHEASTERN
QUADRANT DUE TO CONVERGENT UPPER-LEVEL FLOW OVER THE SOUTHEASTERN
PERIPHERY OF THE SYSTEM AND UPPER-LEVEL DRY AIR ENTRAINMENT.
HOWEVER, UPPER-LEVEL POLEWARD AND EQUATORWARD OUTFLOW REMAIN
VIGOROUS ELSEWHERE. DVORAK INTENSITY ESTIMATES HAVE JUMPED
SIGNIFICANTLY OVER THE PAST SIX HOURS. THEY PEAKED AT AROUND
191730Z WITH MEDIUM GRAY SURROUNDED BY WHITE YIELDING A DT6.0 (115
KNOTS), HOWEVER, THE EYE QUICKLY DEGRADED AND UNOFFICIAL DATA-T
ESTIMATES NOW RANGE FROM T5.0 TO T5.5. THE CIMSS ADT ESTIMATES HAVE
REMAINED LOWER AT 80 KNOTS USING AN EMBEDDED CENTER SCENE TYPE
WHILE AIDT ESTIMATES ARE AT 96 KNOTS. THE INITIAL INTENSITY
ASSESSMENT REMAINS CHALLENGING DUE TO THE FLUCTUATIONS IN THE
DVORAK INTENSITY ESTIMATES AND THE TRANSIENT EYE CHARACTERISTICS.
THE INITIAL INTENSITY IS ASSESSED AT 85 KNOTS BASED ON A BLEND OF
ALL THE DVORAK AND ADT ESTIMATES WITH MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYERED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T5.0 - 90 KTS
   CIMSS ADT: 79 KTS AT 191815Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: SIGNIFICANT UPWELLING OF COOLER WATERS.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: SIGNIFICANT CHANGE TO THE INITIAL
INTENSITY AND PEAK FORECAST INTENSITY DUE TO RECENT EYE FORMATION.
OFF-CYCLE WARNING ISSUED TO BETTER REFLECT THIS IMPORTANT INITIAL
AND FORECAST INTENSITY CHANGE.

FORECAST DISCUSSION: THE JTWC FORECAST TRACK REMAINS HIGHLY
CONSISTENT WITH THE PREVIOUS FORECAST TRACKS. TC 13S IS TRACKING
ALONG THE NORTHWEST PERIPHERY OF A STR POSITIONED TO THE SOUTHEAST
AND EAST, AND IS FORECAST TO TRACK GENERALLY WEST-SOUTHWESTWARD
THROUGH TAU 48. THERE IS QUITE A BIT OF UNCERTAINTY IN THE
INTENSITY FORECAST CONSIDERING THE TRANSIENT NATURE OF THE EYE, 
HOWEVER, THE SYSTEM SHOULD INTENSIFY TO 105 KNOTS WITHIN THE NEXT 24 
HOURS AND MAINTAIN THIS THROUGH TAU 48. IF THE SYSTEM CAN DEVELOP A
ROUND, MORE PERSISTENT EYE, THE INTENSITY, POTENTIALLY, CAN PEAK AT
HIGHER VALUES. HOWEVER, LOW OCEAN HEAT CONTENT VALUES AND THE
UPWELLING OF COOLER WATER REMAIN THE PRIMARY LIMITING FACTOR. AFTER
TAU 48, THE SYSTEM WILL TURN SOUTHWESTWARD TOWARD A WEAKNESS IN THE
STR PRODUCED BY AN APPROACHING DEEP MIDLATITUDE UPPER-LEVEL TROUGH.
TC 13S IS EXPECTED TO CONTINUE TRACKING SOUTHWESTWARD OVER
MADAGASCAR WITH RAPID WEAKENING OVER MOUNTAINOUS TERRAIN FROM TAU 66 
THROUGH TAU 96. NEAR TAU 120, TC 13S WILL COMMENCE SUBTROPICAL 
TRANSITION AS THE SYSTEM INTERACTS WITH AN UPPER-LEVEL SUBTROPICAL 
TROUGH.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC
FORECAST TRACK WITH MEDIUM CONFIDENCE THROUGH TAU 72. AFTER TAU 72,
THE GUIDANCE DIVERGES WITH A SPREAD OF 310NM AT TAU 120. AS
MENTIONED EARLIER, THERE IS SIGNIFICANT UNCERTAINTY IN THE INITIAL
INTENSITY AND JTWC INTENSITY FORECAST. THE JTWC INTENSITY FORECAST
IS ON THE HIGH END OF THE RELIABLE INTENSITY GUIDANCE ENVELOPE,
ABOVE THE JTWC INTENSITY CONSENSUS (ICNW), WITH DECAY SHIPS (GFS
FIELDS) AND HWRF ALSO PEAKING AT 105 KNOTS. ENSEMBLE INTENSITY
GUIDANCE IS MIXED: BOTH THE COAMPS ENSEMBLE AND ECMWF ENSEMBLE
INDICATE SOME POTENTIAL FOR MODERATE INTENSIFICATION FROM TAU 24 TO
TAU 48 WHILE THE GFS ENSEMBLE (191200Z) INDICATES A LOW PROBABILITY
OF RAPID INTENSIFICATION WITHIN THE NEXT 24 HOURS. ADDITIONALLY,
NONE OF THE RAPID INTENSIFICATION GUIDANCE HAS TRIGGERED.        

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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