Advisories

WDPN31 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (KROVANH) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.8N 126.7E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 98 NM NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROADENING
LOW-LEVEL CIRCULATION WITH MULTIPLE WEAK MESOVORTICES RINGING ITS
PERIPHERY. A NOTABLE MESOVORTEX TO THE WEST OF OKINAWA STANDS OUT
MOST CLEARLY BUT DOES NOT REPRESENT THE CENTER OF THE SYSTEM AS A
WHOLE. ANIMATED RADAR ALSO DEPICTS LOW-MID LEVEL CYCLONIC ROTATION
WITHIN THE AREA OF DEEP CONVECTION IN THE NORTHEAST QUADRANT. A
042318Z SSMIS 37 GHZ MICROWAVE IMAGE CONFIRMED THE BROAD RING OF
CONVECTIVE ACTIVITY SURROUNDING THE WEAK WIND CORE, WHERE THE MOST
VIGOROUS CONVECTION REMAINS IN THE NORTHEAST QUADRANT AND SHALLOWER
CONVECTION PERSISTS ELSEWHERE. AN EARLIER 042128Z RCM-3 SAR PASS
ALSO CONFIRMED THE BROAD AREA OF LOW WIND SPEEDS SUGGESTED BY THE
ANIMATED SATELLITE PRESENTATION. THE EFFECT OF THE MORE STABLE
SURROUNDING DRY AIR MASS IS STILL EVIDENT IN THE WESTERN SEMICIRCLE
BY THE PRESENCE OF SHALLOW CUMULUS IN SHORTWAVE INFRARED IMAGERY.
THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE
POORLY DEFINED CENTER OF THE LOW-LEVEL CIRCULATION IN ANIMATED MSI
AND THE SSMIS MICROWAVE IMAGE. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A 39 KT VMAX IN THE
EARLIER SAR IMAGE AND THE OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW. THE ENVIRONMENT IS CHARACTERIZED AS MARGINAL, WITH WARM SEA
SURFACE TEMPERATURES AND GOOD OUTFLOW ALOFT, OFFSET BY 15-20 KTS OF
MID-LEVEL VERTICAL WIND SHEAR (VWS) AND THE DRY AIR MASS TO THE
WEST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHEASTERN FLANK OF A SUBTROPICAL
RIDGE (STR) POSITIONED OVER NORTHEAST CHINA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 042319Z
   CIMSS ADT: 39 KTS AT 042340Z
   CIMSS AIDT: 42 KTS AT 042340Z
   CIMSS D-MINT: 33 KTS AT 042318Z
   CIMSS D-PRINT: 32 KTS AT 050040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SURROUNDING STABLE AND DRY AIR MASS

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE SYSTEM IS NO LONGER CONFINED TO A
DISCRETE LOW-LEVEL CIRCULATION CENTER AND IS INSTEAD POSITIONED
BASED ON THE CENTER OF THE BROAD AREA OF LOW WIND SPEEDS. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 22W HAS CONTINUED ITS
TREND OF EXPANDING THE LOW-LEVEL CIRCULATION CENTER (LLCC) AND 
ASSOCIATED LOW WIND SPEED AREA OVER THE PAST 6 HOURS. THIS TREND AND 
THE APPEARANCE OF WEAK MESOVORTICES AROUND THE PERIPHERY OF THE BROAD
CIRCULATION INTRODUCE MORE UNCERTAINTY TO THE FORECAST TRACK.
GENERALLY, NUMERICAL MODEL FIELDS DEPICT 22W CONSOLIDATING INTO A
SMALLER LLCC EMBEDDED WITHIN A STILL-LARGER CIRCULATION, WHICH ALSO
INCLUDES WHAT REMAINS OF TROPICAL DEPRESSION (TD) 23W AROUND 500 NM
TO THE EAST. OVERALL, THE FORECAST TRACK REMAINS SIMILAR TO
PREVIOUS FORECASTS, EXCEPT THAT THE TRACK SPEED IN LATER TAUS HAS
SLOWED NOTICEABLY. THE SYSTEM IS EXPECTED TO CONTINUE WITH A
PRIMARILY SOUTHWARD COMPONENT AS IT APPROACHES OKINAWA, THEN
CONTINUE AROUND A COUNTER-CLOCKWISE ARC TOWARD MINAMI DAITOJIMA
THROUGH TAU 60. A STR BUILDING IN FROM THE NORTHEAST IS EXPECTED TO
INDUCE A POLEWARD TURN AND ACCELERATION AFTER TAU 60. THERE REMAINS
A FAIR AMOUNT OF UNCERTAINTY IN THE TRACK DUE TO THE DYNAMIC NATURE
OF THE STEERING ENVIRONMENT, ESPECIALLY IN THE LATER TAUS. IN TERMS
OF INTENSITY, A GRADUAL DECREASE IS FORECAST THROUGHOUT THE ENTIRE
PERIOD; FIRST AS A RESULT OF THE SYSTEM'S MOTION AWAY FROM THE
ENHANCED GRADIENT TO ITS NORTH, THEN AS IT LOSES UPPER-LEVEL
EXHAUST, CONTINUES TO INGEST DRY AIR, AND REMAINS IN AN UNFAVORABLE
SHEAR ENVIRONMENT.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN AGREEMENT ONLY INSOFAR
AS THE GENERAL SHAPE OF THE ARCING TRACK AND THE EVENTUAL POLEWARD
TURN. THE JTWC TRACK FORECAST REMAINS CLOSE TO THE CONSENSUS MEAN
THROUGHOUT THE FORECAST, THOUGH WITH LOW CONFIDENCE GIVEN THE
UNCERTAINTY OF WHERE A MORE DISCRETE CIRCULATION MAY CONSOLIDATE.
MODEL INTENSITY GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE
LATEST MODEL RUN AND THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO
THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE DUE TO THE AFOREMENTIONED
FORECAST UNCERTAINTIES.

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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