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JTWC/05W/#05/07-05 00Z Prognostic Reasoning
WDPN32 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (DANAS) WARNING NR
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 20.2N 117.5E
INITIAL INTENSITY: 45 KTS
GEOGRAPHIC REFERENCE: 368 NM SOUTHWEST OF TAIPEI, TAIWAN
MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
SIGNIFICANT WAVE HEIGHT: 16 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 05W (DANAS) WITH VIGOROUS CONVECTIVE BURSTS OBSCURING
THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 050016Z GMI 89 GHZ
MICROWAVE IMAGE REVEALED A DEFINED BAND OF CONVECTION WRAPPING INTO
THE SYSTEM WITHIN THE SOUTHERN SEMICIRCLE. THE VORTEX HAS BECOME
MORE VERTICALLY ALIGNED AND THE POLEWARD OUTFLOW HAS BECOME LESS
RESTRICTED DUE TO THE NORTHERLY SHEAR LESSENING. THE ENVIRONMENT IS
NOW CHARACTERIZED AS HIGHLY FAVORABLE WITH STRONG RADIAL OUTFLOW
ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE MENTIONED GMI MICROWAVE IMAGE AND THE
ANIMATED MSI. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK
CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE POSITIONED TO THE NORTH AND A NEAR-EQUATORIAL
RIDGE BUILDING TO THE SOUTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T3.0 - 45 KTS
RJTD: T2.5 - 35 KTS
RCTP: T3.0 - 45 KTS
KNES: T3.5 - 55 KTS
CIMSS ADT: 43 KTS AT 050000Z
CIMSS AIDT: 39 KTS AT 050000Z
CIMSS DPRINT: 40 KTS AT 050000Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
VWS: 10-15 KTS
SST: 29-30 CELSIUS
OUTFLOW: STRONG RADIAL
ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
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: TS 05W IS FORECAST TO TRACK SLOWLY NORTHWARD
OVER THE NEXT 12 HOURS AS THE STEERING PATTERN REMAINS COMPETING.
AFTER TAU 12, THE NEAR-EQUATORIAL RIDGE TO THE SOUTHEAST WILL
BUILD AND CAUSE THE STEERING PATTERN TO BECOME MORE DEFINED. 05W
WILL THEN INCREASE TRACK SPEEDS IN THE NORTH-NORTHEASTWARD
DIRECTION, ALONG THE NORTHWESTERN PERIPHERY OF THE RIDGE THROUGH
TAU 72. NEAR TAU 72, RIDGING WILL EXTEND OVER TO THE NORTH OF THE
VORTEX, WHICH WILL CAUSE IT TO MAKE A SHARP WESTWARD TURN INTO
MAINLAND CHINA. REGARDING INTENSITY, 05W IS FORECAST TO NEARLY
RAPIDLY INTENSIFY OVER THE NEXT 24 HOURS AS THE ENVIRONMENT REMAINS
HIGHLY CONDUCIVE. A PEAK INTENSITY OF 80 KTS IS FORECAST TO OCCUR
AROUND TAU 36, AS THE SYSTEM BEGINS TO ENTER THE TAIWAN STRAIT.
INTERACTION WITH TAIWAN AND THE EASTERN COAST OF CHINA WILL CAUSE
05W TO BEGIN MARGINALLY WEAKENING AS IT TRACKS THROUGH THE STRAIT.
NEAR TAU 72, AS THE VORTEX INCHES TOWARD THE COAST, INCREASING LAND
INTERACTION AND DRY AIR ADVECTION FROM THE MOUNTAINS WILL CAUSE THE
SYSTEM TO FURTHER WEAKEN. ONCE 05W MAKES THE SHARP TURN INTO CHINA,
DISSIPATION WILL BE IMMINENT. DISSIPATION IS FORECAST TO OCCUR
AROUND TAU 96, AS THE REMNANT VORTEX TRACKS FURTHER OFF TO THE
WEST.
MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH TAU 72, WITH A 170 NM CROSS-TRACK SPREAD AT TAU
72. ECMWF AND ITS ENSEMBLE MEAN ARE THE MOST WESTWARD LEANING
MEMBERS, KEEPING THE VORTEX CLOSER TO THE COAST OF CHINA THAN THE
REMAINDER OF GUIDANCE SUGGESTS. AFTER TAU 72, MODELS GREATLY
DIVERGE. SOME MODELS TAKE A SHARP TURN TOWARD THE SOUTHWEST (UKMET,
JGSM, AND GFS) WHILE OTHERS TAKE A BROADER TURN TO THE
WEST-NORTHWEST (ECMWF AND GALWEM). THE JTWC TRACK FORECAST IS
PLACED MORE IN LINE WITH THE LATTER SCENARIO WITH LOW CONFIDENCE
AFTER TAU 72. INTENSITY GUIDANCE AGREES ON INTENSIFICATION THROUGH
TAU 36. PEAK INTENSITIES RANGE FROM 70-100 KTS WITH THE HIGHER END
CONSISTING OF THE RAPID INTENSIFICATION AIDS THAT CONTINUE TO
TRIGGER. THE JTWC PEAK IS FORECAST TO BE 80 KTS, IN LINE WITH THE
MULTI-MODEL CONSENSUS. AFTER TAU 48, ALL MODELS DEPICT WEAKENING
THROUGH THE REMAINDER OF THE FORECAST PERIOD. HOWEVER, THE JTWC
INTENSITY FORECAST IS PLACED WITH OVERALL LOW CONFIDENCE DUE TO THE
VORTEX BEING SO CLOSE TO LAND ON EITHER SIDE OF THE TRACK. SMALL
VARIATIONS IN THE TRACK COULD CAUSE LARGE CHANGES TO THE INTENSITY
OF THE STORM AS IT TRAVERSES THE TAIWAN STRAIT.
FORECAST CONFIDENCE:
TRACK 0 - 72 HR: MEDIUM
TRACK 72-120 HR: LOW
INTENSITY 0 - 72 HR: LOW
INTENSITY 72-120 HR: LOW//
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