WDXS31 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (NEVILLE) WARNING 
NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8S 102.6E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 702 NM WEST-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
SYSTEM WITH A SOLID RING OF DEEP CONVECTION SURROUND AN
APPROXIMATELY 10 NM DIAMETER EYE. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON RECENT AGENCY FIXES FROM PGTW, KNES,
AND APRF AND CLEAR EYE FEATURES EVIDENT IN 212215Z SSMIS AND
212237Z RCM-2 SAR IMAGERY. THE INITIAL INTENSITY OF 115 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON SUPPORTING SUBJECTIVE DVORAK
ESTIMATES OF T6.0 FROM PGTW, KNES, AND APRF AND PEAK WIND OF
APPROXIMATELY 110 KNOTS EVIDENT IN DATA FROM THE AFOREMENTIONED
RCM-2 SAR PASS. INTENSIFICATION ENDED ABOUT SIX HOURS AGO, AND THE 
TREND HAS BEEN STEADY SINCE THEN AS FAVORABLE FACTORS, INCLUDING A 
PRONOUNCED POLEWARD OUTFLOW CHANNEL, BEGIN TO FADE.

INITIAL WIND RADII BASIS: 212237Z RCM-2 SAR AND OBJECTIVE BEST
TRACK DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   DEMS: T6.0 - 115 KTS
   APRF: T5.5 - 102 KTS
   CIMSS ADT: 82 KTS AT 212030Z
   CIMSS DPRINT: 105 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 18S WILL TRACK WEST-SOUTHWESTWARD UNDER THE
CONTINUED INFLUENCE OF THE CURRENT STR THROUGH THE FORECAST PERIOD.
ENVIRONMENTAL CONDITIONS WILL DETERIORATE SIGNIFICANTLY OVER THE
NEXT 36 TO 48 HOURS AS THE SYSTEM ENCOUNTERS CONVERGENT FLOW ALOFT
AND INCREASING VERTICAL WIND SHEAR INDUCED BY AN UPPER-LEVEL TROUGH
TO THE WEST, PASSES OVER COOLER WATER, AND ENTRAINS DRIER AIR
ALREADY OBSERVED SURROUNDING THE OUTER PERIPHERIES OF THE SYSTEM.
TC 18S HAS SUFFICIENT SUPPORT TO WEAKEN SLOWLY IN THE NEAR-TERM,
BUT AFTER TAU 12 AN INESCAPABLE TREND TO DISSIPATION BY TAU 72 WILL
COMMENCE.

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECASTS ARE IN VERY GOOD
AGREEMENT REGARDING THE ANTICIPATED SPEED AND DIRECTION OF MOTION
THROUGHOUT THE FORECAST PERIOD. CONSENSUS INTENSITY FORECAST
GUIDANCE, INCLUDING HAFS AND BOTH THE COAMPS-TC DETERMINISTIC AND
ENSEMBLE MODEL SOLUTIONS, SUPPORT A STEADY TO RAPID WEAKENING TREND
THROUGH TAU 72. IN FACT, MODEL GUIDANCE SUGGESTS THAT THE SYSTEM
MAY DISSIPATE EVEN SOONER THAN THE CURRENT FORECAST INDICATES,
WHICH IS QUITE POSSIBLE GIVEN THE ANTICIPATED POOR ENVIRONMENTAL
CONDITIONS AND COMPACT AND SUSCEPTIBLE STRUCTURE OF THE
CIRCULATION.

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