Advisories

WDPN31 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (IN-FA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.4N 166.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 139 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 30W HAS INTENSIFIED WHILE REMAINING QUASI-STATIONARY OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS INCREASINGLY ORGANIZED DEEP CONVECTIVE BANDING WRAPPING
INTO A LOW-LEVEL CIRCULATION EVIDENT IN A 232132Z METOP-B ASCAT
SCATTEROMETER PASS. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE ASCAT DATA AND SATELLITE POSITION FIXES
FROM MULTIPLE REPORTING AGENCIES. THE INITIAL INTENSITY OF 45 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE ABOVE THE SUBJECTIVE DVORAK AND
AUTOMATED INTENSITY ESTIMATES LISTED BELOW BASED ON SMALL AREA OF
NEAR-CENTER 40 TO 45 KNOT WINDS EVIDENT IN THE ASCAT DATA.

INITIAL WIND RADII BASIS: 232132Z METOP-B ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 232340Z
   CIMSS AIDT: 34 KTS AT 232340Z
   CIMSS D-MINT: 34 KTS AT 232254Z
   CIMSS D-PRINT: 37 KTS AT 240010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 30W WILL REMAIN QUASI-STATIONARY OVER
THE NEXT FEW HOURS IN A COMPETING STEERING ENVIRONMENT BETWEEN
NEAR-EQUATORIAL RIDGING TO THE SOUTHEAST AND A SOUTHWARD EXTENSION
OF SUBTROPICAL RIDGING TO THE WEST. BY TAU 12, THE NEAR-EQUATORIAL
RIDGE WILL BUILD THE SOUTHEAST, BECOME THE DOMINANT STEERING
MECHANISM, AND PUSH TS 30W TOWARD A NORTH-NORTHWESTWARD TRAJECTORY.
A BUILDING SUBTROPICAL RIDGE TO THE NORTH WILL EXERT AN INCREASING
INFLUENCE ON STORM MOTION AFTER TAU 48, INDUCING A TEMPORARY
SLOWDOWN. AFTER TAU 72, THE SUBTROPICAL RIDGE WILL BECOME THE
DOMINANT STEERING MECHANISM AND PUSH THE SYSTEM WESTWARD. RAPID
NEAR-TERM INTENSIFICATION IS EXPECTED UNDER THE FAVORABLE
INFLUENCES OF LOW VERTICAL WIND SHEAR AND SUPPORTIVE POLEWARD AND
EQUATORWARD UPPER-LEVEL OUTFLOW BOOSTED BY A TROPICAL UPPER
TROPOSPHERIC TROUGH TO THE NORTH. IN THE EXTENDED RANGE, ADDITIONAL
INTENSIFICATION IS EXPECTED, BUT THE RATE SHOULD SLOW A BIT AS THE
OUTFLOW PATTERN BECOMES LESS FAVORABLE. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE CONTINUES TO TIGHTEN IN
DIRECTION AND SPEED, WITH ALL MODELS DEPICTING A SIMILAR EVOLUTION
OF THE STEERING PATTERN. THE CURRENT JTWC TRACK FORECAST LIES AT
THE MIDPOINT OF AN ENVELOPE OF NEARLY ALL SOLUTIONS THAT IS
BRACKETED BY THE AI GFS ON THE SOUTHERN SIDE AND ECMWF
DETERMINISTIC MODEL ON THE NORTHERN SIDE. SOLUTIONS FAN OUT EVENLY
FROM THE START ACROSS THE DISTRIBUTION, PEAKING AT ABOUT 320 NM OF
SEPARATION BY TAU 120. THE CURRENT TRACK FORECAST IS GENERALLY
CONSISTENT WITH THE PREVIOUS ONE. INTENSITY GUIDANCE IS IN FAIRLY
GOOD AGREEMENT THROUGH THE FORECAST CYCLE, WITH COAMPS-TC A BIT
MORE AGGRESSIVE AND HAFS A BIT LESS AGGRESSIVE IN THE NEAR-TERM.
RAPID INTENSIFICATION AIDS HAVE TRIGGERED ON THE LATEST CYCLE, AND
THE NEAR-TERM INTENSITY FORECAST HAS BEEN INCREASED SLIGHTLY IN
RESPONSE. OTHERWISE, THE CURRENT FORECAST IS CONSISTENT WITH THE
PREVIOUS JTWC INTENSITY FORECAST AND LIES NEAR THE COAMPS-TC, HAFS,
AND GOOGLE DEEPMIND INTENSITIES IN THE EXTENDED PERIOD.

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