WDXS31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (IGGY) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7S 109.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 534 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 11S (IGGY) WITH AN INCREASINGLY EXPOSED LOW-LEVEL
CIRCULATION CENTER AS CONVECTION HAS CONTINUED TO BECOME SHEARED TO
THE EASTERN QUADRANT. THROUGHOUT THE SOUTHERN QUADRANT, A
CYCLONICALLY CURVED CONVECTIVE BAND HAS DEVELOPED, WRAPPING ALONG
THE SYSTEMS WESTERN FLANK, HOWEVER, THE MID- TO UPPER-LEVEL
STRUCTURE APPEARS TO EXHIBIT AN EASTWARD TILT, INDICATIVE OF THE
PRESENT VERTICAL WIND SHEAR (VWS) RANGING BETWEEN 10-15 KTS. ALOFT,
A SUPPORTIVE POLEWARD OUTFLOW CHANNEL HAS PERSISTED, AIDING IN THE
CONTINUED SURFACE INTENSITIES UPWARDS OF 45 KTS. ALTHOUGH SEA
SURFACE TEMPERATURES (SST) (28-29 C) AND UPPER-LEVEL SUPPORT REMAIN
FAVORABLE, THE ENVIRONMENT HAS BECOME MARGINAL OVER THE LAST HOURS,
AS VWS HAS VOID THE SYSTEM OF SUPPORTIVE CONVECTION OVER THE
CENTER. THE INITIAL POSITION HAS BEEN PLACED WITH MEDIUM CONFIDENCE
BASED ON THE AFOREMENTIONED PARTIALLY OBSCURED LLCC REVEALED ON
ANIMATED EIR SATELLITE IMAGERY. THE INITIAL INTENSITY HAS BEEN
ASSESSED WITH MEDIUM CONFIDENCE BASED ON SUBJECTIVE AGENCY DVORAK
ESTIMATES RANGING FROM 35-45 KTS AND CIMSS OBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN EXTENT OF A NEAR
EQUATORIAL RIDGE LOCATED DIRECTLY TO THE EAST AND NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 011729Z
   CIMSS ADT: 55 KTS AT 011730Z
   CIMSS AIDT: 42 KTS AT 011730Z
   CIMSS D-PRINT: 43 KTS AT 011800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 11S IS FORECASTED TO TRACK TOWARD THE
SOUTHEAST OVER THE NEXT 12 HOURS ALONG THE SOUTHWESTERN EXTENT OF
THE NEAR EQUATORIAL RIDGE LOCATED DIRECTLY TO THE NORTH AND
NORTHEAST. FOLLOWING TAU 12, A SUBTROPICAL RIDGE (STR) TO THE
SOUTHWEST OF TC 11S WILL BEGIN BUILDING NORTHEASTWARD, BECOMING THE
PRIMARY STEERING MECHANISM FOR THE REMAINDER OF THE FORECAST
PERIOD. BETWEEN TAU 12 AND TAU 72, THE SYSTEM WILL TRACK GENERALLY
WESTWARD AND THEN WEST-SOUTHWESTWARD ALONG THE NORTHERN PERIPHERY
OF THE STR PREVIOUSLY MENTIONED. BETWEEN TAU 48 AND TAU 72, THE
SUBTROPICAL RIDGE TO THE SOUTH WILL BEGIN WEAKENING AS A NEAR
EQUATORIAL RIDGE TO THE NORTH OF TC 11S BUILDS WESTWARD, DRIVING
THE SYSTEM WEST TOWARD DISSIPATION. REGARDING INTENSITY, TC IGGY IS
FORECASTED TO DEEPEN AND INCREASE TO 50 KTS AS AN UPPER-LEVEL
TROUGH PROGRESS EASTWARD JUST TO THE SOUTHEAST, PROVIDING
ADDITIONAL UPPER-LEVEL OUTFLOW SUPPORT. FOLLOWING TAU 24 AND AS THE
UPPER-LEVEL TROUGH TRACKS OUT OF SUPPORTIVE RANGE, EASTERLY VWS
INCREASING TO ABOVE 20 KTS WILL BEGIN THE SYSTEMS TERMINAL
DISSIPATION PHASE. TC 11S IS EXPECTED TO WEAKEN IN INTENSITY TO 30
KTS BY TAU 72 AS THE SYSTEM ENCOUNTERS EXCESSIVE DRY AIR INTRUSION
AND VWS ABOVE 40 KTS.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AND ARTIFICIAL
INTELLIGENCE (AI) MODELS CONTINUE TO ALIGN IN GOOD AGREEMENT ON THE
TRACK FORECAST THROUGH THE 72 HOUR PERIOD. CROSS-TRACK SPREAD
BETWEEN THE JTWC CONSENSUS MEMBERS IS JUST 78 NM BY TAU 72, WITH
THE ONLY OUTLIER BEING NAVGEM, TRACKING THE SYSTEM NORTHWESTWARD
INTO TAU 36, AND THEN SOUTHWESTWARD INTO TAU 72. THE JTWC TRACK
FORECAST IS ALIGNED CLOSELY WITH THE BULK OF CONSENSUS JTWC
NUMERICAL TRACK GUIDANCE AND AI SOLUTIONS, LENDING HIGH CONFIDENCE
TO THE FORECASTED TRACK. REGARDING INTENSITY, THE MAJORITY OF 
INTENSITY JTWC CONSENSUS MEMBERS ILLUSTRATE SUSTAINED INTENSITIES 
BETWEEN 45-50 KTS THROUGHOUT THE NEXT 24 HOURS. FOLLOWING TAU 24, 
EACH INTENSITY FORECAST MEMBERS CHARACTERIZES A STEADY TERMINAL
DISSIPATION PHASE UNTIL TAU 72, WITH THE EXCEPTION OF COAMPS-TC,
INDICATING A SHARPER WEAKENING PHASE NEAR TAU 48 UNTIL DISSIPATION.
THEREFORE, THE JTWC INTENSITY FORECAST IS ALIGNED CLOSELY WITH THE
INTENSITY CONSENSUS, LENDING MEDIUM CONFIDENCE TO THE INTENSITY
FORECAST. 

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