Advisories

WDPS31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01P (ONE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.7S 163.4W
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 437 NM EAST-NORTHEAST OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 01P DEVELOPING BETTER DEFINED CONVECTIVE BANDING ON
THE WESTERN FLANK, WITH AN EXPANDING CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). ENVIRONMENTAL
CONDITIONS ARE ASSESSED TO BE FAVORABLE, WITH WARM (27-28 C) SEA
SURFACE TEMPERATURES (SSTS), LOW (5-10 KTS) VERTICAL WIND SHEAR
(VWS), AND GOOD RADIAL OUTFLOW ALOFT. THE INITIAL POSITION IS
ASSESSED WITH LOW CONFIDENCE DUE TO THE OBSCURED LLCC, POSITIONED
ON THE SOUTHEASTERN EDGE OF THE CDO. THE INITIAL INTENSITY IS
ASSESSED WITH HIGH CONFIDENCE BASED ON GOOD AGREEMENT ACROSS AGENCY
DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS ADT: 41 KTS AT 161740Z
   CIMSS AIDT: 40 KTS AT 161740Z
   CIMSS D-MINT: 43 KTS AT 161438Z
   CIMSS D-PRINT: 41 KTS AT 161710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 01P IS FORECAST TO TRACK SOUTH TO
SOUTHEASTWARD FOR THE REMAINDER OF THE FORECAST PERIOD AS IT IS
STEERED BY THE SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. TRACK
SPEED IS EXPECTED TO INCREASE AS 01P ROUNDS THE AXIS OF THE STR,
TURNS MORE SOUTHEASTWARD, AND BEGINS INTERACTION WITH THE
MID-LATITUDE WESTERLIES. EXTRATROPICAL TRANSITION (ETT) IS EXPECTED
TO BEGIN BY TAU 72 AS 01P NEARS THE BAROCLINIC ZONE, WITH
COMPLETION OF ETT EXPECTED NO LATER THAN TAU 96. REGARDING
INTENSITY, A SHORT TERM INTENSIFICATION PERIOD IS EXPECTED OUT TO A
PEAK OF 65 KTS BETWEEN TAUS 24 AND 36 AS TC 01P REMAINS WITHIN WARM
SSTS, LOW VWS, AND FAVORABLE OUTFLOW ALOFT. AFTER THIS POINT, A
WEAKENING TREND WILL CONTINUE FOR THE REMAINDER OF THE FORECAST
PERIOD AS 01P CROSSES THE 26 C ISOTHERM AND VWS INCREASES TO 25-35
KTS BY TAU 48 AS THE SYSTEM NEARS THE UPPER-LEVEL WESTERLIES.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON A
SOUTHEASTWARD TRACK OUT TO TAU 72, BUT EXPANDING THEREAFTER, RESULTING 
IN A CROSS-TRACK SPREAD OF 300 NM BY TAU 96. ALONG-TRACK SPREAD AT
THAT POINT IS 150 NM, ALTHOUGH THE MULTI-MODEL CONSENSUS AND GOOGLE
DEEPMIND REMAIN IN GOOD AGREEMENT AND WITHIN THE MIDDLE OF THE 
GUIDANCE FOR THE ENTIRETY OF THE FORECAST PERIOD. THE OFFICIAL JTWC 
FORECAST TRACK IS THEREFORE LAID WITH HIGH CONFIDENCE  OUT TO TAU 72 
AND MEDIUM CONFIDENCE THEREAFTER. MODEL INTENSITY GUIDANCE IS IN GOOD
AGREEMENT ON A SHORT TERM INTENSIFICATION AND PEAK BETWEEN 60 AND
70 KTS BETWEEN TAUS 24 AND 36, WITH THE ONLY OUTLIER OF DECAY SHIPS
(GFS-BASED) SHOWING A MUCH LOWER PEAK. A FEW RAPID INTENSIFICATION
AIDS HAVE POPULATED, HOWEVER THE OFFICIAL JTWC FORECAST REFLECTS A
RATE JUST BELOW THAT, INCREASING 25 KTS IN 24 HOURS, IN GOOD
AGREEMENT WITH THE REMAINDER OF THE MESOSCALE MODELS AND THE GOOGLE
DEEPMIND. GOOGLE DEEPMIND WEAKENS THE SYSTEM MUCH MORE RAPIDLY
AFTER TAU 36, WHILE THE BULK DEPICTS A MORE GRADUAL TREND, WHICH IS
WHAT THE OFFICIAL JTWC FORECAST FAVORS AFTER TAU 36. INTENSITY
FORECAST CONFIDENCE IS ASSESSED WITH MEDIUM CONFIDENCE THROUGHOUT
BASED ON THE UNCERTAINTY OF THE WEAKENING TREND AFTER THE PEAK
INTENSITY.

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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