Advisories

WDPS31 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01P (ONE) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.8S 163.3W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 482 NM EAST-NORTHEAST OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION WRAPPING AROUND AN OBSCURED LOW-LEVEL CIRCULATION CENTER
(LLCC). DURING THE PAST SIX HOURS, THE CONVECTIVE STRUCTURE HAS
IMPROVED, WITH ENHANCED RADIAL OUTFLOW AND PARTICULARLY ROBUST
POLEWARD OUTFLOW. A 160520Z SSMIS PASS INDICATED EXTENSIVE
RAINBANDS IN ALL BUT THE NORTHEAST QUADRANT, AS WELL AS A PARTIAL
INNER CORE. THE ENVIRONMENT IS CONDUCIVE TO FURTHER DEVELOPMENT,
CONSISTING OF WARM SEA SURFACE TEMPERATURES (SST) OF 28-29 DEGREES
CELSIUS, VERY RICH DEEP-LAYER MOISTURE, AND MODERATE UPPER-LEVEL
DIVERGENCE. ALTHOUGH THE 800-250 MB VERTICALLY AVERAGED WIND FIELD
INDICATES LOW SHEAR OF 5-10 KTS, THE MID-LEVEL SHEAR IS ELEVATED AT
15-20 KTS. BASED ON THE DVORAK ESTIMATES FROM PGTW, PHFO, AND NFFN,
ALL AT T2.5, THE SYSTEM HAS BEEN DESIGNATED A 35-KT TROPICAL
CYCLONE. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE,
EXTRAPOLATED FROM THE SSMIS DATA AND HEDGED TOWARD THE AGENCY
FIXES.

INITIAL WIND RADII BASIS: EXTRAPOLATION OF SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN FLANK OF A LOW- TO MID-LEVEL
SUBTROPICAL RDGE (STR) CENTERED NEAR 12S 135W

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: ABUNDANT DEEP-LAYER MOISTURE

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 01P WILL CONTINUE ON A SOUTH-SOUTHEASTWARD
TRAJECTORY ALONG THE WESTERN PERIPHERY OF A STR THROUGH TAU 36.
THEREAFTER, THE SYSTEM WILL ROUND THE SOUTHERN PERIPHERY OF THE STR
AND TURN EASTWARD, ACCELERATING INTO THE DEEP-LAYER WESTERLY FLOW.
MODERATE MID-LEVEL SHEAR WILL PERSIST THROUGH TAU 24. HOWEVER, WARM
SST AND A VERY MOIST ATMOSPHERE WILL SUPPORT STEADY INTENSIFICATION
TO A PEAK OF 65 KTS BY TAU 36. AFTER TAU 36, SSTS WILL DECREASE TO
BELOW 26 DEGREES CELSIUS, WHILE VWS WILL STEADILY INCREASE TO 40
KTS BY TAU 60. CONSEQUENTLY, THE FORECAST CALLS FOR STEADY
WEAKENING FROM TAU 36 THROUGH TAU 60. THEREFORE, THE FORECAST CALLS
FOR STEADY WEAKENING FROM TAU 36 TO TAU 60, FOLLOWED BY A SLOWER
RATE OF WEAKENING AS THE SYSTEM BROADENS OUT AND UNDERGOES
EXTRATROPICAL TRANSITION (ETT). TC 01P WILL ENTER THE BAROCLINIC
ZONE BY TAU 72 AND MOVE BENEATH THE JET STREAM. ETT WILL COMPLETE
BY TAU 96.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH THE
CORE GUIDANCE ENVELOPE SHOWING A SOUTH-SOUTHEASTWARD MOTION THROUGH
TAU 36 FOLLOWED BY AN EASTWARD TURN. CROSS-TRACK SPREAD AMONG THE
CORE GROUP OF MODELS INCREASES FROM 75 NM AT TAU 36 TO 85 NM AT TAU
72. NAVGEM AND HAFS-A ARE THE PRIMARY OUTLIERS, DEPICTING AN
EARLIER EASTWARD TURN. THE JTWC TRACK FORECAST LIES WITHIN THE CORE
MODEL CLUSTER AND IS BASED ON A BLEND OF THE AI-MODEL MEAN AND THE
MULTI-MODEL CONSENSUS (CONW), WHILE ALIGNING CLOSELY WITH DEEPMIND.
INTENSITY GUIDANCE FROM HAFS-A AND DEEPMIND IS SIMILAR, INDICATING
STEADY INTENSIFICATION TO A PEAK OF 60-65 KTS AT TAU 36.
THEREAFTER, DEEPMIND INDICATES STEADY TO RAPID WEAKENING TO 20 KTS
BY TAU 96. THE JTWC INTENSITY FORECAST ALIGNS WITH HAFS-A AND
DEEPMIND THROUGH TAU 48, THEN LEANS TOWARD A BLEND OF GFS AND ECMWF
GUIDANCE AT TAU 72 AND TAU 96.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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