WDXS31 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (FREDDY) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4S 109.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 486 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 27 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM 11S CONTINUES TO WEAKEN IN THE FACE OF PERSISTENT
EASTERLY WIND SHEAR. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS THAT WHILE A BALL OF DEEP CONVECTION HAS BEEN
SUSTAINED OVER THE PAST SIX HOURS NEAR THE ASSESSED LOW LEVEL
CIRCULATION CENTER (LLCC), THE SHARP EASTERN EDGE OF THE
CONVECTION INDICATES THE MODERATE EASTERLY SHEAR IS STILL KICKING AND 
NOT ALLOWING FOR CONSOLIDATION OF THE LOW-LEVEL CORE. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON A PARTIALLY
EXPOSED LLCC EVIDENT IN ANIMATED PROXY VISIBLE SATELLITE IMAGERY,
ALONG WITH A SHORT EXTRAPOLATION OF A WELL-DEFINED LLCC EVIDENT IN
A 091111Z RCM-1 SAR PASS. THE INITIAL INTENSITY IS ASSESSED WITH
HIGH CONFIDENCE. THIS IS WELL BELOW AGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T4.0 (65 KTS), THOUGH THE FINAL-T NUMBERS FROM 
ALL AGENCIES WERE DOWN TO T3.5 (55 KNOTS), AS WAS THE DMN AND
OPEN-AIIR AND SATCON. HOWEVER, THE NOTED SAR PASS SHOWED ONLY A FEW 
PIXELS OF 49 KNOT WINDS SCATTERED AROUND THE SYSTEM, WITH THE 
PREDOMINATE WIND FIELD BEING BETWEEN 40-45 KNOTS. HENCE, THE INITIAL 
INTENSITY IS REDUCED TO 50 KNOTS AT ANALYSIS TIME. THE PERSISTENT 
SHEAR CONTINUES TO OFFSET OTHERWISE FAVORABLE SST AND OUTFLOW
CONDITIONS, CREATING A MARGINAL ENVIRONMENT.

INITIAL WIND RADII BASIS: SAR DATA 

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   DEMS: T4.0 - 65 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 53 KTS AT 091055Z
   CIMSS ADT: 51 KTS AT 091130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MODERATE WESTWARD OUTFLOW.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 11S (FREDDY) HAS CHARTED A BIT OF A
MEANDERING COURSE OVER THE PAST 12 HOURS, JUMPING UP TO THE
NORTHWEST AND NOW FLATTING OUT ON A DUE WEST TRAJECTORY, DUE TO
THE STEERING LEVEL LOWERING AS THE SYSTEM HAS WEAKENED AND THE
MID-LEVEL FLOW IS MORE SOUTHEASTERLY THAN THE DEEP-LAYER MEAN.
WHILE THE SUBTROPICAL RIDGE (STR) TO THE SOUTH REMAINS TO PRIMARY
STEERING MECHANISM THROUGH THE FORECAST PERIOD, SUBTLE CHANGES IN
ORIENTATION MEAN THAT TC 11S WILL TRACE A GRACEFUL ARC THAT
REACHES A POINT NEAR 15S AROUND TAU 48, BEFORE TURNING BACK TO THE
SOUTHWEST THROUGH THE REMAINDER OF THE FORECAST. INTENSITY IS A
BIT OF A STICKY ISSUE, AS THE VARIOUS MODELS WIDELY DIVERGE ON THE
STRENGTH OF THE VERTICAL WIND SHEAR THROUGH THE FORECAST PERIOD.
COMPARING THE CIMSS VWS ESTIMATE WITH THE MODELS INDICATES GFS IS
CURRENTLY VERIFYING THE BEST, AND GOING FORWARD, GFS SUGGESTS
WEAKENING SHEAR THROUGH TAU 48. HWRF SHOWS A SIMILAR TREND AND
PROVIDES GOOD SUPPORT TO THE FORECAST WHICH CALLS FOR STEADY
INTENSITY FOR THE NEXT 12 HOURS WHILE THE SYSTEM CONSOLIDATES INTO
A BETTER-DEFINED CORE. ONCE THE CORE IS REESTABLISHED THE SYSTEM
WILL INTENSIFY QUICKLY, UP TO 85 KNOTS BY TAU 48 UNDER IMPROVED
ENVIRONMENTAL CONDITIONS. AFTER TAU 48, SHEAR LOOKS TO PICK UP
AGAIN AND 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: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT THROUGH TAU 72, WITH ALL CONSENSUS MEMBERS
ENSCONCED IN A 75NM ENVELOPE, LENDING HIGH CONFIDENCE TO THIS PORTION 
OF THE TRACK FORECAST. BEYOND TAU 72, THE MODELS SPREAD OUT QUICKLY, 
WITH THE GALWEM, UKMET, UKMET ENSEMBLE, ECMWF AND ECMWF ENSEMBLE
TRACKING THE SYSTEM WEST TO WEST-NORTHWEST THROUGH TAU 120.
MEANWHILE THE GFS, NAVGEM AND THE GFS ENSEMBLE TAKE THE SYSTEM ON
A MORE SOUTHWESTWARD TRACK, FEELING THE EFFECTS OF A BREAK IN THE
STR TO THE SOUTH A BIT MORE THAN THE EUROPEAN MODELS. THE JTWC
FORECAST FAVORS THE GFS SOLUTION AND TAKES THE SYSTEM MORE
WEST-SOUTHWESTWARD, THOUGH CONFIDENCE FALLS TO MEDIUM DURING THIS
PHASE OF THE FORECAST. INTENSITY GUIDANCE IS NOT IN AGREEMENT,
WITH A SIGNIFICANT SPREAD IN PEAK INTENSITIES BETWEEN 45 KTS (DECAY-
SHIPS AND COAMPS-TC NAVGEM) AND 115 KTS (HWRF AND CTR1).
ADDITIONALLY, THE COAMPS-TC ENSEMBLE INTENSITY PROBABILITIES
CONTINUE TO SHOW A 40 PERCENT CHANCE OF RAPID INTENSIFICATION (RI)
THROUGH TAU 36. THE JTWC FORECAST REMAINS CONSISTENT WITH THE
PREVIOUS FORECAST AND LIES ABOUT 10 KNOTS ABOVE THE CONSENSUS MEAN
BUT ABOUT 20 KTS LOWER THAN THE HWRF PEAK. HOWEVER, WITH SUCH A
LARGE SPREAD IN THE GUIDANCE, CONFIDENCE IN THE INTENSITY FORECAST
IS VERY LOW. 

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