Advisories

WDPN31 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (IN-FA) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0N 165.0E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 448 NM SOUTH-SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 30W IS GRADUALLY BECOMING BETTER ORGANIZED.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) OVER THE PAST 12
HOURS DEPICTS DEEP CENTRAL CONVECTION THAT HAS STRUGGLED TO
PERSIST, LIKELY DUE TO MODERATE MID-LEVEL SOUTHERLY SHEAR
ENTRAINING DRY AIR INTO THE CIRCULATION. HOWEVER, DURING THE PAST
FEW HOURS, VORTICAL HOT TOWERS HAVE DEVELOPED WITHIN THE CENTRAL
DENSE OVERCAST (CDO), AND A POLEWARD OUTFLOW CHANNEL FEEDING INTO
AN UPPER-LEVEL TROUGH TO THE NORTHEAST HAS DEVELOPED. AN EARLIER
242015Z SSMIS PASS REVEALED A DEVELOPED INNER CORE AND A VERTICALLY
ALIGNED VORTEX. TS 30W IS TRAVERSING A GENERALLY FAVORABLE
ENVIRONMENT OF VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30
DEGREES CELSIUS, MODERATE TO STRONG DIVERGENCE ALOFT, AND MODERATE
VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE, CENTERED BETWEEN THE PGTW AND RJTD FIXES. THE
INITIAL INTENSITY IS SET AT 60 KTS WITH MEDIUM CONFIDENCE, BASED ON
A BLEND OF THE T3.5 AND T4.0 DVORAK CLASSIFICATIONS FROM PGTW AND
RJTD, RESPECTIVELY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 52 KTS AT 250252Z
   CIMSS ADT: 55 KTS AT 250540Z
   CIMSS AIDT: 46 KTS AT 250540Z
   CIMSS D-MINT: 60 KTS AT 250253Z
   CIMSS D-PRINT: 51 KTS AT 250540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 30W IS MOVING NORTH-NORTHWESTWARD AT 5-6
KTS. THIS MOTION WILL CONTINUE THROUGH TAU 12. AT THAT TIME, A
TROUGH DRAPED OVER HONSHU WILL GRADUALLY NUDGE THE SUBTROPICAL
RIDGE (STR), PRESENTLY POSITIONED SOUTHEAST OF HONSHU, EASTWARD.
THERE IS A SLIGHT CHANCE THAT A SLOWER EASTWARD SHIFT OF THE STR
WILL ALLOW A BRIEF NORTHEASTWARD TURN BEFORE A VERY SHARP WESTWARD
TURN BETWEEN TAU 24 AND TAU 48. THIS ALTERNATIVE SCENARIO COULD
DELAY THE SUBSEQUENT FORECAST POSITIONS BY AS MUCH AS FOUR HOURS.
BY TAU 48, A DEEPER TROUGH PASSING OVER THE KOREAN PENINSULA AND
APPROACHING HONSHU WILL CAUSE THE STR TO REORIENT AND CONSOLIDATE
NEARLY DUE NORTH OF TS 30W. CONSEQUENTLY, THE SYSTEM WILL BEGIN TO
SLOW BY TAU 24, TURN WESTWARD THROUGH TAU 48, AND ACCELERATE
WESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 120. WHILE MODERATE
MID-LEVEL SHEAR WILL PERSIST FOR AT LEAST THE NEXT 24 HOURS, THE
VERY WARM SST AND STRONG POLEWARD OUTFLOW CHANNEL MAY ALLOW THE
COMPACT VORTEX TO UNDERGO A 24-HOUR PERIOD OF RAPID INTENSIFICATION
(RI). AFTER TAU 24, THE SLOWER MOTION OF TS 30W AND THE LOSS OF THE
POLEWARD OUTFLOW CHANNEL WILL SUPPRESS CONTINUED INTENSIFICATION AS
THE POTENTIAL FOR UPWELLING INCREASES AND UPPER-LEVEL DIVERGENCE
DECREASES. ONCE THE SYSTEM GAINS SUFFICIENT FORWARD MOTION, THE
FORECAST CALLS FOR REINTENSIFICATION TO AT LEAST 115 KTS BY TAU 96.

MODEL DISCUSSION: TRACK GUIDANCE HAS COME INTO BETTER AGREEMENT,
WITH HAFS-A AND GFS SHOWING LESS OF A BRIEF NORTHEASTWARD TURN.
JGSM, WHICH CLOSELY FOLLOWED THIS GROUP, HAS NOW FALLEN IN LINE
WITH THE CORE CLUSTER, WHICH DEPICTS AN OUTRIGHT WESTWARD TURN.
CROSS-TRACK SPREAD INCREASES TO 240 NM AT TAU 120, WITH NAVGEM AS
THE NORTHERNMOST SOLUTION AND GALWEM BRINGING THE SYSTEM WITHIN 70
NM OF TINIAN. ALONG-TRACK SPREAD ALSO INCREASES AFTER TAU 24,
ALTHOUGH MOST SOLUTIONS ARE WITHIN 120 NM OF EACH OTHER AT TAU 120.
THE SLOW OUTLIERS ARE HWRF, GFS, AND JGSM. THE JTWC FORECAST TRACK
HAS SHIFTED SLIGHTLY SOUTHWARD AFTER TAU 48 AND IS PLACED ALONG A
BLEND OF THE AI-MODEL MEAN AND THE MULTI-MODEL CONSENSUS. BOTH ARE
NEAR THE GOOGLE DEEPMIND AND ECMWF SOLUTIONS AND LIE NEAR THE
CENTER OF THE CORE GUIDANCE ENVELOPE. CONSIDERABLE SPREAD EXISTS
AMONG THE INTENSITY AIDS. NEARLY ALL MODELS DEPICT SIGNIFICANT
NEAR-TERM INTENSIFICATION. HAFS-A AND COAMPS-TC REMAIN THE MOST
AGGRESSIVE SOLUTIONS, BRINGING THE SYSTEM TO 115-120 KTS BY TAU 36.
THE JTWC INTENSITY FORECAST IS MORE CONSERVATIVE AND MORE CLOSELY
ALIGNED WITH DEEPMIND THROUGH TAU 24. MODELS LARGELY SHOW STEADY
INTENSITY OR SOME WEAKENING FROM TAU 36 TO TAU 60, FOLLOWED BY
ADDITIONAL INTENSIFICATION TO 115-130 KTS BETWEEN TAU 96 AND TAU
120. THE JTWC INTENSITY FORECAST IS SLIGHTLY LOWER THAN DEEPMIND AT
TAU 36 AND TAU 48, BUT TRENDS CLOSER TO DEEPMIND THEREAFTER.

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