WDPS31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED)     
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5S 155.4E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 559 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE
OBLONG CENTRAL DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL 
CIRCULATION CENTER, WITH RAPIDLY CYCLING DEEP CONVECTION AND WEAK 
SPIRAL BANDING. UNFORTUNATELY, USEFUL MICROWAVE IMAGERY HAS BEEN 
SPARSE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 
261052Z ASCAT-C BULLSEYE IMAGE REVEALING A WELL-DEFINED CENTER AND 
EXTENSIVE GALE-FORCE WINDS OVER THE SOUTHERN SEMICIRCLE. THE INITIAL 
WIND RADII ARE BASED ON A DETAILED ANALYSIS OF THIS ASCAT IMAGE WITH 
HIGH CONFIDENCE. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS FAVORABLE, 
WITH WARM SST VALUES AND MODERATE POLEWARD OUTFLOW SUSTAINING THE CDO 
FEATURE. HOWEVER, SATELLITE IMAGERY CLEARLY SHOWS NORTHERLY PRESSURE 
ON THE SYSTEM, WHICH IS LIMITING EQUATORWARD VENTING AND, 
CONSEQUENTLY, HINDERING THE DEVELOPMENT OF AN EYE AND BETTER SPIRAL 
BANDING. THE INITIAL INTENSITY OF 85 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE NARROW RANGE OF BOTH SUBJECTIVE AND CIMSS 
OBJECTIVE INTENSITY ESTIMATES FROM 76 TO 90 KNOTS. A 260758Z RCM2 SAR 
PASS HAD PREVIOUSLY INDICATED A MAXIMUM WIND OF 75 KNOTS, ALSO WITHIN 
THE RANGE OF THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL STEERING RIDGE POSITIONED
TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   ABRF: T4.5 - 77 KTS
   CIMSS ADT: 76 KTS AT 261200Z
   CIMSS AIDT: 77 KTS AT 261200Z
   CIMSS D-PRINT: 80 KTS AT 261130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 18P IS EXPECTED TO REMAIN 
UNDER THE PERSISTENT NORTHWESTERLY VERTICAL WIND SHEAR THROUGH THE 
FORECAST PERIOD, WHICH WILL CONTINUE TO HAMPER DEVELOPMENT AS THE 
SYSTEM TRACKS SOUTHWARD. HOWEVER, THERE IS A BRIEF WINDOW OF 
OPPORTUNITY FROM TAU 36 TO TAU 60 WHERE ENHANCED POLEWARD OUTFLOW INTO 
THE SUBTROPICAL JET TO THE SOUTH MAY ALLOW FOR MODEST INTENSIFICATION 
AS SUGGESTED BY HAFS-A (FORECASTS REINTENSIFICATION TO 90 KNOTS BY TAU 
48). THIS SCENARIO APPEARS REASONABLE AND IS REFLECTED IN THE JTWC 
INTENSITY FORECAST. AFTER TAU 72, AN APPROACHING MAJOR SHORTWAVE 
TROUGH WILL WEAKEN THE STR TO THE SOUTH AND RE-ORIENT THE STR TO THE 
EAST ALLOWING TC 18P TO GRADUALLY TURN SOUTH-SOUTHEASTWARD FROM TAU 96 
TO TAU 120. WEAKENING IN THE EXTENDED FORECAST PERIOD IS LIKELY AS THE 
SYSTEM BECOMES EMBEDDED IN THE NORTHERN PERIPHERY OF THE MAJOR 
SHORTWAVE TROUGH.    

MODEL DISCUSSION: IN GENERAL, DETERMINISTIC GUIDANCE IS IN GOOD CROSS-
TRACK AGREEMENT, WITH A 115NM CROSS-TRACK SPREAD AT TAU 120. HOWEVER, 
THERE IS A CLEAR BIFURCATION IN THE ALONG-TRACK SPREAD, WITH AFUI AND 
NVGI RAPIDLY TRACKING THE SYSTEM SOUTHEASTWARD WHILE THE BULK OF THE 
REMAINING GUIDANCE FAVORS A SLOWER SOUTH-SOUTHEASTWARD TRACK. THE JTWC 
TRACK FORECAST FAVORS THE SLOWER SOLUTIONS, WHICH MAKE MORE SENSE IN 
THIS TYPE OF SYNOPTIC PATTERN. THE BULK OF THE EPS SOLUTIONS ARE 
SLOWER WITH TAU 120 FORECAST POSITIONS GENERALLY EQUATORWARD OF 26S 
LATITUDE. THE BULK OF THE RELIABLE INTENSITY GUIDANCE INDICATES THE 
SYSTEM WILL MAINTAIN TYPHOON STRENGTH WINDS THROUGH TAU 120.

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