WDPS31 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9S 172.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 229 NM EAST-NORTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 18P WITH A SLOWLY CONSOLIDATING LOW-LEVEL CIRCULATION
CENTER (LLCC) AS BUILDING AND DEEP CONVECTION HAS BEGUN WRAPPING
CYCLONICALLY AROUND THE SOUTHERN QUADRANT OVER THE LAST FEW HOURS.
MODERATE VERTICAL WIND SHEAR (VWS) BETWEEN 15-20 KTS REMAINS
EVIDENT THROUGHOUT THE WESTERN SEMICIRCLE, ADDING PRESSURE TO THE
PRIMARY CONVECTIVE STRUCTURE SLIGHTLY DISLOCATED TO THE SOUTH AND
SOUTHEAST OF THE LLCC. THE ENVIRONMENT HAS BEEN ANALYZED AS
MARGINALLY FAVORABLE, WITH WARM SEA SURFACE TEMPERATURES BETWEEN
29-30 C, PERSISTENT VWS, AND ROBUST POLEWARD OUTFLOW ALOFT. THE
INITIAL POSITION HAS BEEN PLACED WITH LOW CONFIDENCE BASED ON
EXTRAPOLATION FROM A 280427Z 91 GHZ SSMIS IMAGE AND ANIMATED MSI.
THE INITIAL INTENSITY HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE
BASED ON SUBJECTIVE AGENCY DVORAK ESTIMATES ALIGNED AT T2.5 (35
KTS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS D-PRINT: 23 KTS AT 280600Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 18P IS FORECASTED TO CONTINUE ROUNDING THE
EASTERN PERIPHERY OF THE STR AXIS CENTERED DIRECTLY TO THE
SOUTHEAST THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. OVER THE
NEXT 12 HOURS, THE CYCLONE WILL TRACK SOUTH-SOUTHEASTWARD, BECOMING
GENERALLY SOUTH-SOUTHWESTWARD THEREAFTER UNTIL DISSIPATION OVER
WATER BY TAU 36 ALONG THE EASTERN EXTENT OF THE WESTWARD MIGRATING
STR. REGARDING INTENSITY, TC 18P IS EXPECTED TO UNDERGO MODERATE
INTENSIFICATION THROUGHOUT THE NEXT 12 HOURS AS THE ENVIRONMENT
REMAINS MARGINALLY FAVORABLE WITH WARM SEA SURFACE TEMPERATURES,
SUPPORTIVE UPPER-LEVEL POLEWARD OUTFLOW, AND MARGINAL VWS.
FOLLOWING TAU 12, THE ENVIRONMENT WILL BECOME INCREASINGLY HOSTILE,
WITH VWS INCREASING TO ABOVE 30 KTS AT THE SAME TIME DRY AIR
ENTRAINMENT ERODES THE SURFACE LLCC. BETWEEN TAU 12 AND TAU 36,
SURFACE INTENSITIES ARE FORECASTED TO WEAKEN TOWARD 30 KTS AS THE
ENVIRONMENT BECOMES LARGELY UNFAVORABLE WITH VWS ABOVE 40 KTS AND
EXCESSIVE DRYING THROUGHOUT THE MID-LEVELS. COMPLETE DISSIPATION
OVER WATER IS FORECASTED BY TAU 36.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE AND ARTIFICIAL
INTELLIGENCE (AI) GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH THE 36
HOUR FORECAST PERIOD, WITH A CROSS-TRACK SPREAD OF 47 NM EXPECTED
AT TAU 12, GRADUALLY INCREASING TO 95 NM BY TAU 36. NAVGEM IS
CURRENTLY THE ONLY OUTLIER, ILLUSTRATING THE LONE TRACK
SOUTHWESTWARD THROUGHOUT THE ENTIRETY OF THE FORECAST. THE JTWC
TRACK FORECAST HAS BEEN PLACED CLOSELY TO MULTI-MODEL CONSENSUS,
OMITTING THE NAVGEM SOLUTION, LENDING HIGH CONFIDENCE TO THE JTWC
TRACK FORECAST. REGARDING INTENSITY, ALL MEMBERS OF THE JTWC
MULTI-MODEL CONSENSUS CHARACTERIZE A SHORT INTENSIFICATION PHASE
OVER THE NEXT 12 HOURS, WITH A TERMINAL WEAKENING PHASE THEREAFTER.
THE INTENSITY SPREAD AT THE CYCLONES PERIOD OF MAXIMUM INTENSITY IS
ABOUT 10 KTS, WITH THE GFS DETERMINISTIC SOLUTION NEARING 50 KTS AT
TAU 12. FOLLOWING TAU 12, EACH JTWC INTENSITY CONSENSUS MEMBER
SHOWS GRADUAL WEAKENING AT VARYING DEGREES UNTIL COMPLETE
DISSIPATION BY TAU 36. THE JTWC INTENSITY FORECAST HAS BEEN
ASSESSED WITH MEDIUM CONFIDENCE AND ALIGNED JUST ABOVE THE JTWC
INTENSITY CONSENSUS.  

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