Advisories

WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (KROVANH) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.4N 127.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 120 NM NORTH-NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 22W WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) OBSCURED BY PERSISTENT CONVECTION IN THE NORTHEAST
QUADRANT. THE SATELLITE PRESENTATION IN THE REMAINING QUADRANTS IS
THAT OF STABLE LOW CLOUDS WRAPPING INTO THE SLIGHTLY ELONGATED
LLCC. A ROBUST POLEWARD OUTFLOW CHANNEL SUPPORTED BY A PASSING JET
STREAK IS STILL EVIDENT IN ANIMATED WATER VAPOR IMAGERY, WHICH
CONTINUES TO SUPPORT CONVECTION IN THE NORTHEAST QUADRANT. A
041452Z OCEANSAT-3 SCATTEROMETRY IMAGE REVEALED THE HIGHLY
ASYMMETRIC WIND FIELD AROUND THE CENTER OF THE SYSTEM, WITH A SWATH
OF 45 KT WINDS IN THE NORTHERN SEMICIRCLE WHERE THE PRESSURE
GRADIENT HAS ENHANCED THE WIND SPEEDS. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF THE POORLY
DEFINED LLCC IN ANIMATED EIR AND EXTRAPOLATION FROM THE CENTER IN
THE SCATTEROMETRY IMAGE. THE INITIAL INTENSITY OF 45 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SCATTEROMETRY WINDS,
HOWEVER, THE PRESSURE GRADIENT IS LIKELY RELAXING AS THE SYSTEM
MOVES EQUATORWARD AND THEREFORE GRADUALLY REDUCING THE WIND SPEEDS
IN THE NORTHERN SEMICIRCLE. THE ENVIRONMENT IS CHARACTERIZED AS
MARGINAL, WITH WARM SEA SURFACE TEMPERATURES AND GOOD OUTFLOW ALOFT
BEING OFFSET BY LOW-MODERATE VERTICAL WIND SHEAR (VWS) AND THE DRY
AIR MASS SURROUNDING THE VORTEX IN ALL BUT THE NORTHEAST QUADRANT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHEASTERN FLANK OF A RIDGE
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: 37 KTS AT 041704Z
   CIMSS ADT: 34 KTS AT 041750Z
   CIMSS AIDT: 38 KTS AT 041750Z
   CIMSS D-MINT: 35 KTS AT 041705Z
   CIMSS D-PRINT: 30 KTS AT 041820Z

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: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 22W (KROVANH) HAS TRACKED SLOWLY
SOUTHWESTWARD OVER THE PAST 6 HOURS AS THE DEEP SUBTROPICAL RIDGE
(STR) OVER EASTERN CHINA HAS STARTED TO EXERT A STEERING INFLUENCE.
THE TRACK IS FORECAST TO CONTINUE GENERALLY SOUTHWARD AS 22W
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 AMONG THE MEAN TRACK OF THE
GUIDANCE THROUGHOUT THE FORECAST WITH MEDIUM CONFIDENCE THROUGH TAU
72 AND LOW CONFIDENCE THEREAFTER. MODEL INTENSITY GUIDANCE IS
SPLIT, WITH THE EXPERIMENTAL GOOGLE DEEPMIND AND HAFS-A MAINTAINING
A STEADY INTENSITY AROUND 40 KTS, WHILE THE REMAINDER OF GUIDANCE
AGREES ON A GRADUAL WEAKENING TREND. THE JTWC INTENSITY FORECAST IS
PLACED AMONG THE LATTER GROUP AND CLOSE TO THE CONSENSUS MEAN WITH
MEDIUM CONFIDENCE, GIVEN THE EXPECTED ENVIRONMENTAL CONDITIONS.

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