WDXS31 PGTW 100300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (FREDDY) WARNING 
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3S 108.4E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 530 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SLIGHTLY
ASYMMETRIC CENTRAL DENSE OVERCAST CLOUD LAYER THAT CONTINUES TO BE
SHEARED BY EASTERLY WIND SHEAR, WITH A LOW-LEVEL CIRCULATION THAT
HAS BECOME OBSCURED BY DEEP CONVECTION. A 092015Z SSMIS 89GHZ
MICROWAVE IMAGE REVEALS A DEEP CURVED CONVECTIVE BAND OVER THE
NORTHWEST QUADRANT WRAPPING INTO A WELL-DEFINED LOW-LEVEL
CIRCULATION. A 092220Z SAR WINDSPEED PASS SHOWS A WELL-DEFINED
SYSTEM THAT HAS STRENGTHENED OVER THE PAST SIX HOURS. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE SAR PASS ALONG
WITH THE AFOREMENTIONED SSMIS MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 70 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
SAR IMAGE IN COMBINATION WITH PGTW AND KNES DVORAK CURRENT
INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   APRF: T4.0 - 65 KTS
   CIMSS ADT: 51 KTS AT 092330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: OVER THE PAST 12 HOURS TROPICAL CYCLONE 11S
HAS TRACKED GENERALLY EAST-NORTHEASTWARD AT 8 KNOTS. OVER THE NEXT
12 HOURS 11S IS FORECAST TO ACCELERATE NORTHEASTWARD AS THE SYSTEM
TRANSITS ALONG THE NORTHWEST PERIPHERY OF THE DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTH. THE SYSTEM WILL CONTINUE TO
TRANSIT NORTHEASTWARD QUICKLY THROUGH TAU 48, DUE TO THE SYSTEM'S
POSITION WITHIN THE STR. AFTER WHICH, TC 11S WILL REACH A POINT
NEAR 15S BEFORE TURNING AND TRACKING IN A WEST-SOUTHWESTWARD
DIRECTION THROUGH THE REMAINDER OF THE FORECAST. TC 11S WILL
STEADILY INTENSIFY OVER THE NEXT 48 HOURS AS DETERMINISTIC MODELS
AGREE THAT VERTICAL WIND SHEAR (VWS) IS EXPECTED TO DECREASE. THIS
WILL ALLOW THE SYSTEM TO ULTIMATELY ACHIEVE A PEAK INTENSITY OF 85
KNOTS BY TAU 48. AFTER TAU 48, SHEAR LOOKS TO PICK UP AGAIN AS THE
SYSTEM MOVES INTO RELATIVELY COOLER (26-27C) WATERS AND UPPER-LEVEL
FLOW BECOMES INCREASINGLY CONVERGENT, LEADING TO SLOW BUT STEADY
WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: THE BULK OF THE DETERMINISTIC GUIDANCE REMAINS IN
TIGHT AGREEMENT WITH ONLY A 35 TO 75NM SPREAD IN SOLUTIONS FROM TAU
12 TO TAU 72. WITH THE NAVGEM BEING THE OUTLIER TO THE LEFT OF THE
TRACK. BETWEEN TAU 96 AND TAU 120, TRACK GUIDANCE SPREADS FROM
135NM TO 210NM. THEREFORE, THERE IS HIGH CONFIDENCE THROUGH TAU 72
AND LOW CONFIDENCE THEREAFTER AS THE SPREAD INCREASES THERE IS
SIGNIFICANT UNCERTAINTY IN THE JTWC INTENSITY FORECAST AS MODEL
GUIDANCE. HWRF AND GFS CONTINUE TO INDICATE A GRADUAL
INTENSIFICATION BY TAUS 72-96, WHILE COAMPS-TC SHOW A GRADUAL
DECREASE BY TAU 72. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED
WITH LOW CONFIDENCE GIVEN THE DISAGREEMENT IN THE INTENSITY MODELS.

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