Wati

WDPS31 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01P (WATI) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.8S 163.2W
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 437 NM EAST OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 01P (WATI) ONCE AGAIN SLOWING IN TRACK SPEED, POSSIBLY
HAVING TAKEN A BRIEF WESTWARD JOG OR LOOP BEFORE RESUMING AN OVERALL 
SOUTH-SOUTHEASTWARD TRACK, ALTHOUGH THE LOW LEVEL CIRCULATION CENTER 
(LLCC) REMAINS OBSCURED. A 171615Z SSMIS PASS REVEALED A VERTICALLY 
ALIGNED MICROWAVE EYE FEATURE, WHILE IT STRUGGLES TO FORM ANY KIND OF 
DISCERNIBLE EYE IN EIR IMAGERY. THE MICROWAVE DATA ALSO SHOWS A STRONG 
CONVECTIVE BAND EXTENDING FROM THE SOUTHERN EDGE UP THE EASTERN FLANK, 
BUT OVERALL SLIGHTLY COOLING CLOUD TOPS. ENVIRONMENTAL CONDITIONS ARE 
ASSESSED TO BE MARGINALLY FAVORABLE AS THE SYSTEM IS WITHIN 26-27 C 
SEA SURFACE TEMPERATURES BUT HAS LOW (10-15 KTS) VERTICAL WIND SHEAR 
(VWS) AND STRONG POLEWARD AND RADIAL OUTFLOW ALOFT. THE INITIAL 
POSITION IS PLACED WITH LOW CONFIDENCE DUE TO THE OBSCURED NATURE BUT 
IN GOOD AGREEMENT WITH ALL FIXES. THE INITIAL INTENSITY IS ALSO 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SPREAD BETWEEN AGENCY 
DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES. THE INITIAL WIND RADII ARE  
ASSESSED WITH LOW CONFIDENCE BASED ON THE LACK OF MORE RECENT WIND  
SPEED DATA, BUT DEPICT A SIMILAR ASYMMETRICAL WIND FIELD AS WAS SHOWN  
IN THE 170734Z METOP-B ASCAT DATA.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T4.0 - 65 KTS
   CIMSS SATCON: 60 KTS AT 171616Z
   CIMSS ADT: 55 KTS AT 171740Z
   CIMSS AIDT: 61 KTS AT 171740Z
   CIMSS D-MINT: 57 KTS AT 171546Z
   CIMSS D-PRINT: 49 KTS AT 171910Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   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 01P IS FORECAST TO CONTINUE SOUTHEASTWARD
FOR THE REMAINDER OF THE FORECAST PERIOD AS IT RECURVES THE 
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST-NORTHEAST. TRACK SPEED 
WILL ALSO ACCELERATE AS THE SYSTEM ENCOUNTERS THE MID-LATITUDE 
WESTERLIES. EXTRATROPICAL TRANSITION (ETT) IS FORECAST TO BEGIN BY TAU 
48 AS THE SYSTEM NEARS THE BAROCLINIC ZONE, AND COMPLETE ETT BY TAU 
60. REGARDING INTENSITY, A BRIEF PERIOD OF INTENSIFICATION IS FORECAST 
OUT TO TAU 12 WHILE 01P REMAINS IN A MARGINALLY FAVORABLE 
ENVIRONMENTAL CONDITIONS BEFORE BEGINNING A STEADY WEAKENING TREND 
THEREAFTER AS WATI CROSSES THE 26 C ISOTHERM BY TAU 24 AND MID-LEVEL 
VWS INCREASES TO 20-30 KTS BY TAU 36 AS IT NEARS THE STRONG UPPER-
LEVEL WESTERLIES. WHILE NOT INCLUDED IN THE FORECAST, IT IS POSSIBLE 
THAT WATI HAS ALREADY REACHED ITS PEAK INTENSITY AND COULD BEGIN 
WEAKENING EARLIER THAN ANTICIPATED, DEPENDING ON THE EFFECTS OF THE 
COOLER SSTS ON THE SYSTEM, WHICH WILL BE THE EARLIEST DETERIORATING 
CONDITION TO OCCUR. HOWEVER, WATI IS EXPECTED TO REMAIN AT A TROPICAL 
STORM STRENGTH AT THE TIME ETT COMPLETES.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT OF A
SOUTHEASTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD, WITH A 
CROSS-TRACK SPREAD OF 100 NM AT TAU 60, EXCLUDING THE OUTLIERS OF 
NAVGEM AND GALWEM. ALONG-TRACK SPREAD AT THAT POINT IS LARGER AT 150 
NM DUE TO THE ACCELERATION DURING ETT. THE OFFICIAL JTWC FORECAST IS 
PLACED WITH HIGH CONFIDENCE, HEDGING BETWEEN THE MULTI-MODEL AND AI 
CONSENSUS. MODEL INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT OF A 
SHORT TERM INTENSIFICATION OR PLATEAU AT TAU 12 FOLLOWED BY WEAKENING 
THEREAFTER, WITH THE EXCEPTION OF GFS AND HWRF WHICH DEPICT AN 
IMMINENT WEAKENING. THE OFFICIAL JTWC INTENSITY FORECAST IS THUS 
ASSESSED WITH MEDIUM CONFIDENCE DUE TO THE SHORT TERM UNCERTAINTY, 
JUST ABOVE THE MULTI-MODEL CONSENSUS. 

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