WDPS31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (ALFRED) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8S 154.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 537 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 18P NEARLY QUASI-STATIONARY WHILE IN A WEAK STEERING
ENVIRONMENT. CYCLICAL DEEP CONVECTION OBSCURES THE LOW-LEVEL
CIRCULATION CENTER(LLCC). A SLOT OF CLEAR SKIES INDICATES DRY AIR
WRAPPING AROUND THE NORTHERN PERIPHERY OF THE SYSTEM AND EXPOSES
THE LOW-LEVEL CLOUD BANDS TIGHTLY WINDING INTO CENTER. WATER VAPOR
IMAGERY REVEALS WEAK RADIAL UPPER-LEVEL DIVERGENCE WITH A STRONG
POLEWARD OUTFLOW CHANNEL FEEDING INTO THE SUBTROPICAL JET TO THE
SOUTH. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED
ON A 241130Z METOP-C AMSU-B 89GHZ MICROWAVE IMAGE DEPICTING A
SHEARED CIRCULATION WITH DEEP CONVECTION BLOWN TO THE WEST OF THE
LOW-LEVEL BANDING WRAPPING INTO CENTER. THE INITIAL INTENSITY OF 65
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY FIXES
LISTED BELOW.

INITIAL WIND RADII BASIS: 241041Z METOP-B ASCAT DATA

CURRENT STEERING MECHANISM: IN A WEAK STEERING ENVIRONMENT SLIGHTLY
INFLUENCED BY A WEAK DEEP-LAYER RIDGE TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 66 KTS AT 241300Z
   CIMSS ADT: 51 KTS AT 241300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG 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 WILL SLOWLY MEANDER
SOUTHWARD INCREASING TRACK SPEED AS A WEAK NEAR EQUATORIAL RIDGE TO
THE WEST BUILDS WESTWARD GRADUALLY THROUGHOUT THE FORECAST PERIOD.
BETWEEN TAU 96 AND 120, THE SYSTEM WILL BEGIN TO TRACK
SOUTHWESTWARD DRIVEN BY THE SAME BUILDING RIDGE. THE SYSTEM WILL
GRADUALLY INTENSIFY OVER THE NEXT 48 HOURS WHILE IN AN ENVIRONMENT
WITH HIGHLY FAVORABLE UPPER-LEVEL DIVERGENCE, MODERATE 10-15KT
VERTICAL WIND SHEAR, AND WARM SEA SURFACE TEMPERATURES. HOWEVER,
THE SLOW MOTION OF THE TC IN THE NEAR-TERM FORECAST WILL RESULT IN
UPWELLING AND A DEPLETION OF OCEAN HEAT CONTENT, CREATING A
MARGINALLY FAVORABLE ENVIRONMENT FOR DEVELOPMENT AND GRADUAL RATE
OF INTENSIFICATION. AFTER TAU 48, THE SYSTEM WILL MOVE OUT OF THE
REGION OF UPWELLING INTO FAVORABLE SEA SURFACE TEMPERATURES BUT
VERTICAL WIND SHEAR INCREASES 15-20KT AND DRY AIR WILL IMPINGE THE
NORTHWESTERN PERIPHERY OF THE SYSTEM. THE WEAKENING TREND OF TC 18P
WILL BE SLOW AND GRADUAL IN THE CAREFUL BALANCE OF FAVORABLE AND
UNFAVORABLE FEATURES, WEAKENING TO 70KTS BT THE END OF THE
FORECAST. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TC 18S WILL REMAIN SLOW AND QUASI-STATIONARY IN THE NEAR-TERM
FORECAST. BY TAU 120, THE MODEL SOLUTIONS SPREAD TO 465NM BOUNDED
BY ECMWF TO THE WEST AND NAVGEM TO THE EAST DUE TO VARYING
INTERPRETATIONS OF HOW FAR AND STRONGLY THE DEEP-LAYER STEERING
RIDGE WILL BUILD. THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT
THE TC WILL GRADUALLY INTENSIFY TO A PEAK BETWEEN TAU 24-48
FOLLOWED BY A PERIOD OF GRADUAL WEAKENING FOR THE REMAINDER OF THE
FORECAST.

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