Advisories

WDPN31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (KROVANH) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.5N 131.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 314 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 
22W (KROVANH) WITH A BROAD AND ELONGATED LOW-LEVEL CIRCULATION CENTER 
(LLCC) THAT HAS BECOME OBSCURED BY FLARING CONVECTION ALONG THE 
SOUTHERN SEMICIRCLE. THE WESTERN PORTION OF THE CIRCULATION IS LOOSE 
WITH A WEAK NORTHERLY COMPONENT. THE SHARP UPPER-LEVEL TROUGH TO THE 
WEST OF THE SYSTEM HAS HINDERED THE FORMATION OF CONVECTION IN THE 
AREA. A 010045Z METOP-B ASCAT PASS REVEALED THE ELONGATED CIRCULATION 
WITH WINDS OF 30-35 KTS WITHIN THE SOUTHERN SEMICIRCLE. THE ASCAT ALSO 
SHOWED THAT THE RADIUS OF MAXIMUM WINDS (RMW) HAS SHRUNK TO BELOW 80 
NM, CAUSING THE SYSTEM TO NOW BE IDENTIFIED AS A TROPICAL STORM. THE 
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 
ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED PRIMARILY ON PERSISTENCE FROM THE AFOREMENTIONED 
ASCAT PASS. ENVIRONMENTAL ANALYSIS INDICATES THAT 22W IS IN A 
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD 
OUTFLOW ALOFT, SUBSIDENCE OVER THE WESTERN PERIPHERY, LOW TO MODERATE
(15-20 KTS) NORTHERLY VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA
SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 010045Z METOP-B ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AND A NEAR
EQUATORIAL RIDGE (NER) TO THE SOUTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS D-PRINT: 27 KTS AT 010600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR AND SUBSIDENCE ALONG THE WESTERN
PERIPHERY CAUSED BY AN UPPER-LEVEL TROUGH

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 22W IS FORECAST TO CONTINUE TRACKING SLOWLY
OVER THE NEXT 12 HOURS AS THE SYSTEM REMAINS PLACED WITHIN THE 
COMPETING STEERING PATTERN. AFTER TAU 12, THE NER TO THE SOUTHWEST
WILL WEAKEN AND MOVE OFF TO THE WEST, ALLOWING FOR THE STR TO BECOME 
THE PRIMARY STEERING MECHANISM. THIS WILL CAUSE 22W TO TRACK 
NORTHWESTWARD THROUGH TAU 60, NEAR THE RYUKYU ISLANDS. AFTER TAU 60, 
AN UPPER-LEVEL TROUGH WILL BREAK DOWN THE STEERING RIDGE, CAUSING THE 
SYSTEM TO BE PLACED WITHIN A WEAK STEERING ENVIRONMENT. THE ACTUAL 
TRACK OF THE SYSTEM IS HIGHLY UNCERTAIN AFTER TAU 60, BUT THE JTWC 
TRACK FORECAST CALLS FOR A SLOW EASTWARD MOVEMENT THROUGH TAU 120 AS A 
BUILDING NER TO THE SOUTH LOOSELY CONTROLS THE STEERING. IN TERMS OF 
INTENSITY, 22W IS FORECAST TO MARGINALLY INTENSIFY THROUGH TAU 60 AS 
THE BROAD VORTEX ATTEMPTS TO CONSOLIDATE AND THE UPPER-LEVEL TROUGH TO 
THE WEST FILLS. AFTER TAU 60, NORTHWESTERLY SHEAR IS FORECAST TO 
INCREASE, CAUSING THE SYSTEM TO GRADUALLY WEAKEN THROUGH TAU 120. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN VERY POOR AGREEMENT
THROUGHOUT THE ENTIRE FORECAST PERIOD WITH SIGNIFICANT SPREAD. THE
VARIOUS AI-BASED MODELS SHOW A MUCH SLOWER POLEWARD MOVEMENT, THAT 
TAKES THE VORTEX CLOSER TO OKINAWA. THEY ALSO SHOW THE EASTWARD TURN 
SOUTH OF OKINAWA RATHER THAN NORTH OF THE ISLAND. OTHER MODELS SHOW A 
RATHER CLEAN RECURVE TOWARD SOUTHERN JAPAN (GFS). THIS MODEL 
DISCREPANCY IS DUE TO THE LARGE DIFFERENCE IN TRACK SPEEDS IN THE NEAR 
TERM. IF THE SYSTEM IS FASTER, A TRACK AROUND THE STEERING RIDGE 
TOWARD JAPAN IS MORE LIKELY. THE JTWC TRACK FORECAST IS CURRENTLY 
PLACED NEAR THE CONSENSUS, BUT CHANGES TO THE TRACK FORECAST ARE 
LIKELY ONCE THE FORWARD MOTION OF 22W BECOMES MORE APPARENT. IN TERMS 
OF INTENSITY, MODELS GENERALLY AGREE ON A NEAR STEADY INTENSITY 
THROUGHOUT THE ENTIRE FORECAST PERIOD. THE GOOGLE DEEPMIND DOES SHOW A 
SLIGHTLY HIGHER PEAK, CLOSER TO 55 KTS THOUGH. OVERALL, THE JTWC 
INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS WITH MEDIUM 
CONFIDENCE. 

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