WDPS31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.0S 151.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 357 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY CONSOLIDATING SYSTEM, WITH AN AREA OF DEEP, SYMMETRICAL
CONVECTION WITH VERY COLD CLOUD TOPS AND OVERSHOOTING TOPS
EXCEEDING -90C. HOWEVER, WHILE THE CONVECTION APPEARS TO BE
SYMMETRICAL AND THE ASSUMPTION BEING THAT THE LOW LEVEL CIRCULATION
CENTER (LLCC) IS VERTICALLY ALIGNED, THIS APPEARS TO NOT BE THE
CASE. A 221739Z SSMIS 36GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED
LOW EMISSIVITY REGION (LER), WITH SHALLOW BANDING FEATURES WRAPPING
AROUND IT, DISPLACED NORTHWEST OF THE DEEP CONVECTION AREA. THE
INITIAL POSITION USING THE SSMIS IMAGE NOTED ABOVE, WAS PLACED WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED WITH LOW
CONFIDENCE, AS THE AGENCIES ARE ALL REPORTING DVORAK CURRENT
INTENSITY ESTIMATES OF T2.5 OR BELOW, WHILE THE CIMSS ADT AND
SATCON ARE RAPIDLY INCREASING TO 40 KNOTS OR HIGHER. THE INITIAL
INTENSITY IS SET TO ALIGN WITH THE MORE AGGRESSIVE OBJECTIVE
ESTIMATES. THE ENVIRONMENT IS HIGHLY FAVORABLE, WITH MINIMAL WIND
SHEAR, VERY WARM SSTS AND ROBUST POLEWARD OUTFLOW PLUS WEAKER
EQUATORWARD OUTFLOW. THE ONLY HINDRANCE AT THE MOMENT IS THE TILTED
VORTEX STRUCTURE AND PRESENCE OF A BIT OF DRY AIR ON THE
SOUTHWESTERN SIDE OF THE SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR EQUATORIAL RIDGE (NER) CENTERED NORTHEAST OF THE SOLOMON
ISLANDS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   ABRF: T2.5 - 35 KTS
   CIMSS SATCON: 38 KTS AT 221500Z
   CIMSS ADT: 41 KTS AT 221730Z
   CIMSS AIDT: 33 KTS AT 221730Z
   CIMSS D-PRINT: 30 KTS AT 221800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: WEAK EQUATORWARD OUTFLOW; TILTED VORTEX. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   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 18P (EIGHTEEN) IS EXPECTED TO TRACK
EAST-NORTHEASTWARD ALONG THE SOUTHWESTERN SIDE OF A DEEP NER OVER
THE NEXT 12 TO 24 HOURS. AFTER TAU 24, THE NER WILL SLOWLY WEAKEN
AND ULTIMATELY MERGE INTO A VERY LARGE SUBTROPICAL RIDGE (STR) THAT
WILL EXTEND FROM THE SOLOMONS ALL THE WAY TO SOUTH OF AMERICAN
SAMOA. THE POTENTIAL DEVELOPMENT OF ANOTHER POTENTIAL TROPICAL
CYCLONE EAST OF VANUATU WILL WEAKEN THE STEERING GRADIENT AFTER TAU
36 AND TC 18P WILL SLOW DOWN AS IT TRACES A GENTLE ARC TOWARDS THE
SOUTHEAST. AFTER TAU 48, THE STEERING RIDGE STRENGTHENS AND PUSHES
SOUTH NEAR VANUATU, AND TC 18P WILL ACCELERATE TOWARDS THE SOUTH
THROUGH THE REMAINDER OF THE FORECAST PERIOD ALONG THE WESTERN SIDE
OF THIS RIDGE. IN TERMS OF THE INTENSITY, THE ENVIRONMENT IS PRIMED
TO SUPPORT A FAST PACE OF INTENSIFICATION, WITH THE POSSIBILITY OF
RAPID INTENSIFICATION. IN THE NEXT 12 HOURS HOWEVER,
INTENSIFICATION SHOULD BE RELATIVELY SLOW AS THE SYSTEM IS STILL
NOT VERTICALLY ALIGNED. AXISYMMETRIZATION AND ROBUST DIVERGENCE
ALOFT WILL FUEL A PERIOD OF RAPID INTENSIFICATION (RI) FROM TAU 12
TO TAU 36, WITH THE POSSIBILITY OF AN EVEN LONGER PERIOD OF RI AND
A MORE EXTREME RATE OF INTENSIFICATION, AS SHOWN BY SOME OF THE RI
AIDS NOTED BELOW. THE SYSTEM SHOULD BE AROUND TAU 48 AND THEN BEGIN
TO SLOWLY WEAKEN DUE TO INCREASING NORTHERLY SHEAR. THE CURRENT
FORECAST PEAKS THE SYSTEM AT 85 KNOTS BUT SOME RI GUIDANCE SUGGESTS
THE PEAK COULD BE AS MUCH AS 30 KNOTS HIGHER. THE STRONGER THE
SYSTEM CAN GET PRIOR TO TAU 48, THE LESS THE SHEAR WILL IMPACT IT,
WHICH MAY RESULT IN A SIGNIFICANTLY HIGHER INTENSITY IN THE LATER
FORECAST TAUS. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD
AGREEMENT THROUGH THE FIRST 48 TO 72 HOURS OF THE FORECAST PERIOD,
WITH ALL CONSENSUS MEMBERS IN AGREEMENT WITH THE OVERALL TRACK.
CROSS-TRACK SPREAD INCREASES TO 100NM BY TAU 48, AND TO 165NM BY
TAU 72. GFS AND GALWEM TAKE THE SYSTEM ON A MORE GENTLE ARCING
TRAJECTORY FURTHER TO THE EAST, WHILE THE NAVGEM AND ECMWF DEPICT A
SHARPER TURN WHICH PLACES THEM TO THE WEST OF THE CONSENSUS MEAN.
BY THE END OF THE FORECAST PERIOD, CROSS-TRACK UNCERTAINTY
INCREASES TO 250NM, WHILE ALONG-TRACK SPREAD INCREASES SHARPLY,
WITH THE GFS AND NAVGEM FAR OUTRUNNING THE REMAINDER OF THE MODEL
GUIDANCE. GEFS AND ECEPS ENSEMBLES DEPICT A HIGH DEGREE OF
UNCERTAINTY, WITH A VERY LARGE SPREAD ACROSS MOST OF THE CORAL SEA,
WITH INDIVIDUAL MEMBERS STRETCHING FROM COASTAL AUSTRALIA TO NEW
CALEDONIA. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN
THROUGH TAU 48, THEN CURVES INSIDE IT, HEDGING TOWARDS THE ECMWF
SOLUTION. CONFIDENCE IS HIGH THROUGH 72, THEN MEDIUM THEREAFTER.
ALL OF THE RELIABLE INTENSITY CONSENSUS MEMBERS AGREE THAT THE
SYSTEM WILL INTENSIFY BUT ARE HIGHLY UNCERTAIN AS TO THE AMOUNT OF
INTENSIFICATION. HAFS-A AND COAMPS-TC ARE ON THE LOW END OF THE
SPECTRUM, PEAKING BETWEEN 55-60 KNOTS, WHILE THE SHIPS GUIDANCE
PEAKS AROUND 90 KNOTS. MEANWHILE, RIPA, RICN, FRIA AND RI25 ARE ALL
TRIPPED ON THIS MODEL CYCLE, SHOWING PEAKS AT OR ABOVE 100 KNOTS
WITHIN THE NEXT 48 TO 60 HOURS. THE JTWC FORECAST LIES ABOVE NEARLY
ALL THE GUIDANCE EXCEPT THE RI AIDS, AND ABOUT 5-10 KNOTS ABOVE THE
CONSENSUS MEAN.  

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