WPAC: YAGI - Post-Tropical

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WDPN32 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 18W (EIGHTEEN), LOCATED APPROXIMATELY 556 NM
SOUTHEAST OF KADENA AB, JAPAN, HAS TRACKED NORTHWESTWARD AT 01 KNOT
OVER THE PAST SIX HOURS. ANIMATED EIR SATELLITE IMAGERY SHOWS A
POORLY ORGANIZED SYSTEM WITH THE BULK OF CONVECTION SHEARED
APPROXIMATELY 80 NM WESTWARD OF AN ILL-DEFINED LLC. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE EIR LOOP AND
LINED UP WITH A RECENT BUT PARTIAL ASCAT PASS. THE INITIAL INTENSITY
OF 25 KNOTS IS BASED ON THE DVORAK ESTIMATES OF T1.5 FROM PGTW AND
RJTD AND SUPPORTED BY THE ASCAT IMAGE. UPPER LEVEL ANALYSIS INDICATES
TD 18W IS IN AN AREA OF STRONG (25-30 KNOT) EASTERLY VWS WITH LIMITED
OUTFLOW. HOWEVER, SST IN THE AREA ARE VERY WARM AT 30C. THE CYCLONE
IS EMBEDDED IN THE SOUTHWEST MONSOON FLOW AND IS IN A
QUASI-STATIONARY (QS) MOTION BETWEEN THE SHALLOW NER TO THE SOUTHEAST
AND A DEEP-LAYERED STR TO THE NNW.
3. FORECAST REASONING.
A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE AND SETS THE
FORECAST TRACK PHILOSOPHY FOR THIS SYSTEM.
B. TD 18W WILL REMAIN QS IN THE NEAR-TERM BUT SHOULD EVENTUALLY
TRACK NORTHEASTWARD UNDER THE STEERING INFLUENCE OF THE NER. AFTER
TAU 48, THE STR TO THE NORTHEAST WILL ASSUME STEERING AND DRIVE THE
SYSTEM MORE NORTHWARD AS IT SLIGHTLY INTENSIFIES AND DEEPENS. THE
MARGINAL ENVIRONMENT DESCRIBED IN PARA 2 WILL FUEL THE SLIGHT
INTENSIFICATION TO 35 KNOTS BY TAU 36 AND SUSTAINED TO TAU 72.
C. BEYOND TAU 72, TD 18W WILL CONTINUE TRACKING POLEWARD ALONG THE
WESTERN PERIPHERY OF THE STR TO THE NORTHEAST. THE VWS WILL DECREASE
TO LOWER VALUES (10-15 KNOTS) AS THE TD APPROACHES JAPAN AND ALLOW
FOR SLIGHT INTENSIFICATION TO 40 KNOTS. THERE IS A VERY WIDE SPREAD
IN THE NUMERICAL MODEL GUIDANCE, SPANNING OVER 850 NM IN THE EXTENDED
TAUS. THIS, PLUS THE UNCERTAINTY ASSOCIATED WITH THE INITIAL QS
MOTION LEND LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
NNNN

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WDPN32 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY
509 NM SOUTH-SOUTHEAST OF KADENA AB, JAPAN, HAS TRACKED
NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD, EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH MULTIPLE MESO-VORTICES ROTATING
CYCLONICALLY ABOUT A CENTROID WITH DEEP CONVECTION SHEARED OVER THE
WESTERN SEMICIRCLE DUE TO MODERATE TO STRONG EASTERLY VERTICAL WIND
SHEAR (VWS). VWS IS OFFSET SOMEWHAT BY BROAD UPPER-LEVEL DIFFLUENCE,
WHICH IS FUELING THE PERSISTENT DEEP CONVECTION. A 070635Z SSMIS
91GHZ IMAGE SHOWS SHALLOW BANDING WRAPPING INTO AN ELONGATED, WEAKLY-
DEFINED LLCC. CONSEQUENTLY, THERE IS POOR CONFIDENCE IN THE CURRENT
POSITION. THE INITIAL INTENSITY REMAINS ASSESSED AT 25 KNOTS BASED
ON DVORAK ESTIMATES OF T1.5 (25 KNOTS) FROM KNES AND PGTW AS WELL AS
THE WEAK OVERALL CONVECTIVE STRUCTURE. TD 18W IS POSITIONED ALONG
THE NORTHERN PERIPHERY OF THE LOW-LEVEL NEAR-EQUATORIAL RIDGE (NER)
AND IS TRACKING SLOWLY / ERRATICALLY DUE TO THE WEAK ORGANIZATION OF
THE SYSTEM AND THE WEAK STEERING INFLUENCE.
3. FORECAST REASONING.
A. THE FORECAST TRACK HAS SHIFTED SIGNIFICANTLY AFTER TAU 72 AND
THE FORECAST PHILOSOPHY / NUMERICAL GUIDANCE SUPPORTS A MORE
WESTWARD TRACK OVER THE RYUKYU ISLAND CHAIN.
B. TD 18W IS FORECAST TO TRACK SLOWLY THROUGH TAU 36 UNDER THE
STEERING INFLUENCE OF THE NER. AFTER TAU 36, THE SYSTEM WILL
ACCELERATE POLEWARD AS A SUBTROPICAL RIDGE (STR) BUILDS IN TO THE
EAST AFTER TY 17W RECURVES INTO THE NORTH PACIFIC. ENVIRONMENTAL
CONDITIONS ARE FORECAST TO REMAIN MARGINAL THROUGH TAU 72,
THEREFORE, VERY SLIGHT INTENSIFICATION IS EXPECTED. SPECIFICALLY,
MODERATE TO STRONG (20 TO 30 KNOTS) VWS IS EXPECTED TO HINDER
SIGNIFICANT DEVELOPMENT. NUMERICAL GUIDANCE IS IN POOR AGREEMENT
WITH A 375NM SPREAD IN SOLUTIONS AT TAU 72.
C. AFTER TAU 72, THERE IS INCREASING UNCERTAINTY WITH A 550NM
SPREAD IN SOLUTIONS AT TAU 120. UNFORTUNATELY, UNCERTAINTY IN
POSITIONING WILL LEAD TO ADDITIONAL UNCERTAINTY AND WILL LIKELY
RESULT IN SIGNIFICANT SHIFTS IN THE TRACK UNTIL THE SYSTEM
CONSOLIDATES. HOWEVER, ANALYSIS OF 500MB FIELDS IN THE GFS, NAVGEM,
UKMO AND ECMWF ALL DEPICT A STRONG STR BUILDING OVER WESTERN JAPAN,
THE KOREAN PENINSULA AND THE YELLOW SEA, WHICH SHOULD SUPPORT A
WESTWARD TRACK IN THE EXTENDED PERIOD (ADDITIONALLY, NO EVIDENCE OF
A STRONG SHORTWAVE TROUGH THAT COULD PRODUCE A RECURVE SCENARIO).
DUE TO THE UNCERTAINTY IN THE EARLY PHASE OF THE TRACK, THE SYSTEM
COULD TRACK FURTHER SOUTH OVER OKINAWA. TD 18W IS FORECAST TO
INTENSIFY AT A GREATER RATE AS VWS DECREASES, THEREFORE, THE PEAK
INTENSITY IS FORECAST AT TAU 120 AT 55 KNOTS. OVERALL, THERE IS A
HIGH DEGREE OF UNCERTAINTY (LOW CONFIDENCE) IN THE JTWC FORECAST
TRACK.//
NNNN

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WDPN32 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 18W (EIGHTEEN), LOCATED APPROXIMATELY
512 NM SOUTH-SOUTHEAST OF KADENA AB, JAPAN, HAS TRACKED
NORTH-NORTHWESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED EIR
SATELLITE IMAGERY SHOWS A BROAD, EXPOSED LLC WITH DEEP CONVECTION
SHEARED APPROXIMATELY 40 NM TO THE WEST DUE TO MODERATE TO STRONG
EASTERLY VWS. THE VWS IS SLIGHTLY OFFSET BY AN EQUATORWARD OUTFLOW
WHICH IS FUELING THE PERSISTENT DEEP CONVECTION. THE INITIAL
POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE EIR LOOP AND
LINED UP WITH A MICROWAVE CIRCULATION FEATURE IN THE AMSU-B 071239Z
PASS. THE INITIAL INTENSITY OF 30 KNOTS IS BASED ON THE DVORAK
ESTIMATE OF T2.0 (30 KNOTS) FROM PGTW. TD 18W IS QUASI-STATIONARY
ALONG THE NORTHERN PERIPHERY OF THE LOW-LEVEL NER AND IS TRACKING
SLOWLY / ERRATICALLY DUE TO THE WEAK ORGANIZATION OF THE SYSTEM AND
THE WEAK STEERING INFLUENCE.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TD 18W IS FORECAST TO TRACK SLOWLY THROUGH TAU 24 UNDER THE
STEERING INFLUENCE OF THE NER. AFTER TAU 24, THE SYSTEM WILL
ACCELERATE NORTHWARD THEN NORTH-NORTHWESTWARD AS A STR BUILDS IN FROM
THE EAST. ENVIRONMENTAL CONDITIONS ARE FORECAST TO REMAIN MARGINAL
THROUGH TAU 36, THEREFORE, NO INTENSIFICATION IS EXPECTED. AFTERWARD
INCREASED SUBSIDENCE FROM AN UPPER LEVEL TROUGH AND SUSTAINED STRONG
VWS WILL WEAKEN THE SYSTEM TO 25 KNOTS.
C. AFTER TAU 72, TD 18W WILL TRACK MORE NORTHWESTWARD AS THE STR
CONTINUES TO BUILD. VWS IS EXPECTED TO DECREASE AND POLEWARD OUTFLOW
TO INCREASE AS THE CYCLONE GAINS LATITUDE. THESE WILL ALLOW THE
SYSTEM TO INTENSIFY UP TO 45 KNOTS BY TAU 120. THE NUMERICAL MODEL
GUIDANCE REMAINS SIGNIFICANTLY SPREAD OUT, SPANNING OVER 500 NM BY
TAU 120 WHERE SOME OF THE MODELS INDICATE A MORE POLEWARD TRAJECTORY,
A POSSIBLE INDICATION OF RECURVATURE. IN VIEW OF THIS, THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST TRACK.//
NNNN

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TXPQ29 KNES 072119
TCSWNP

A. 18W (NONAME)

B. 07/2030Z

C. 19.2N

D. 132.0E

E. THREE/HIMAWARI-8

F. T3.0/3.0/D1.0/06HRS

G. IR/EIR/SWIR

H. REMARKS...THIS INTENSITY ESTIMATE WAS DERIVED USING 4 KM IR
DATA. SYSTEM CHARACTERIZED BY SHEAR WITH A LLCC LOCATED LESS THAN 1/2
DEG FROM DG FOR A DT=3.0 MET=2.5 PT=2.5 FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...FISHER

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TPPN10 PGTW 072133

A. TROPICAL DEPRESSION 18W (EIGHTEEN)

B. 07/2100Z

C. 19.09N

D. 132.09E

E. FIVE/HMWRI8

F. T2.0/2.0/D0.5/24HRS STT: S0.0/03HRS

G. IR/EIR

H. REMARKS: 47A/PBO PTLY XPSD LLCC/ANMTN. CNVCTN WRAPS .35 ON
LOG10 SPIRAL YIELDING A DT OF 2.0. MET AND PT AGREE. DBO DT.

I. ADDITIONAL POSITIONS: NONE


LOWE

[NotoSans]

Upgraded to TS YAGI.

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Upgraded to a TS.

18W EIGHTEEN 180808 0000 19.3N 132.5E WPAC 35 996

[doomhaMwx]

TS 1814 (Yagi)
Issued at 06:55 UTC, 8 August 2018

<Analysis at 06 UTC, 8 August>
Scale -
Intensity -
Center position N19°30' (19.5°)
E133°25' (133.4°)
Direction and speed of movement ENE Slow
Central pressure 994 hPa
Maximum wind speed near center 18 m/s (35 kt)
Maximum wind gust speed 25 m/s (50 kt)
≥ 30 kt wind area S 500 km (270 NM)
N 220 km (120 NM)

[doomhaMwx]

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WDPN32 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (YAGI)
WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 18W (YAGI), LOCATED APPROXIMATELY 521 NM
SOUTHEAST OF KADENA AB, HAS TRACKED EAST-NORTHEASTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
SHOWS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEEP
CONVECTION SHEARED TO THE SOUTHWEST. THE INITIAL POSITION IS BASED ON
A 080600Z HIMAWARI VISIBLE SATELLITE IMAGE WHICH SHOWS THE LLCC. THE
INITIAL INTENSITY OF 35 KNOTS IS BASED ON A 080009Z METOP-A ASCAT
IMAGE SHOWING 35 KNOT WINDS, THIS IS HEDGED SLIGHTLY ABOVE A DVORAK
INTENSITY ESTIMATE OF T2.0 (30 KNOTS). ENVIRONMENTAL ANALYSIS SHOWS
THAT TS 18W IS EXPERIENCING UNFAVORABLE VERTICAL WIND SHEAR FROM THE
NORTHEAST TO SOUTHWEST, RANGING BETWEEN 25 AND 30 KNOTS. THIS IS
SLIGHTLY OFFSET BY A MODERATE EQUATORWARD OUTFLOW CHANNEL. HOWEVER,
THERE IS NO POLEWARD OUTFLOW CHANNEL. SEA SURFACE TEMPERATURES ARE
FAVORABLE FOR DEVELOPMENT, NEAR 30 DEGREES CELSIUS. TS 18W IS
DRIFTING EAST-NORTHEASTWARD AS IT REMAINS BETWEEN A SUBTROPICAL RIDGE
(STR) TO THE NORTHWEST AND A NEAR EQUATORIAL RIDGE (NER) TO THE
SOUTHEAST.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 18W WILL SLOWLY TRACK TO THE NORTH OVER THE NEXT 24 HOURS AS
IT REMAINS UNDER THE INFLUENCE OF THE AFOREMENTIONED STR AND NER.
WARM SEA SURFACE TEMPERATURES AND SLIGHTLY IMPROVING VERTICAL WIND
SHEAR WILL LEAD TO A SLIGHT INCREASE IN INTENSITY, REACHING A PEAK
INTENSITY OF 40 KNOTS. BEYOND TAU 24, TS 17W WILL BEGIN TO TRACK
NORTHWESTWARD UNDER THE INFLUENCE OF THE STR TO THE NORTHEAST.
DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT, THEREFORE THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST TRACK.
C. BEYOND TAU 72, THE STR TO THE NORTHEAST WILL CONTINUE TO STEER
TS 18W TO THE NORTHWEST. INTENSITY WILL REMAIN NEAR 35 KNOTS THROUGH
THIS PORTION OF THE FORECAST. THERE IS A WIDE SPREAD IN DYNAMIC MODEL
GUIDANCE DURING THIS PORTION OF THE FORECAST. ECMWF AND UKMET FAVOR
NORTHWEST TRACK AFTER TAU 96 WHILE NAVGEM AND JGSM FAVOR A
NORTHEASTWARD TURN BEYOND TAU 96. THE JTWC FORECAST TRACK IS PLACED
NEAR THE MULTI-MODEL CONSENSUS AND FAVORS THE ECMWF AND UKMET MODELS.
THERE IS OVERALL LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
TRACK.//
NNNN

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TPPN10 PGTW 080915

A. TROPICAL STORM 18W (YAGI)

B. 08/0850Z

C. 19.61N

D. 133.68E

E. THREE/HMWRI8

F. T2.5/2.5/D1.0/24HRS STT: D0.5/03HRS

G. IR/EIR/VIS/MSI

H. REMARKS: 19A/PBO XPSD LLCC/ANMTN. CNVCTN SHEARED 55NM FROM
LLCC YIELDS A DT OF 2.5. MET IS A 2.5 AND PT IS A 2.0. DBO DT.

I. ADDITIONAL POSITIONS:
08/0427Z 19.43N 133.27E AMS2
08/0622Z 19.53N 133.57E SSMS
08/0653Z 19.18N 133.63E MMHS


RICHARDSON

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WDPN32 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (YAGI) WARNING NR
09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 18W (YAGI), LOCATED APPROXIMATELY 462 NM WEST-
SOUTHWEST OF IWO TO, HAS TRACKED NORTH-NORTHEASTWARD AT 08 KNOTS
OVER THE PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH FAIR
CONFIDENCE BASED ON ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY WHICH DEPICTS AN EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH DEEP CONVECTION SHEARED TO THE WEST. THIS POSITION IS SUPPORTED
BY A 081637Z AMSR2 36 GHZ IMAGE WHICH SHOWS SHALLOW BANDING WRAPPING
INTO THE LLCC WITH DEEP CONVECTION OVER THE WEST QUADRANT. THE
INITIAL INTENSITY OF 35 KNOTS IS BASED ON A PGTW DVORAK ESTIMATE OF
T2.5 (35 KNOTS). UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT
WITH MODERATE TO STRONG (20 TO 30 KNOTS) VERTICAL WIND SHEAR (VWS)
OFFSET BY GOOD EQUATORWARD OUTFLOW. TS 18W IS TRACKING ALONG THE
NORTHERN PERIPHERY OF A WEAK NEAR-EQUATORIAL RIDGE (NER) TO THE
SOUTH.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 18W WILL TRACK NORTHWARD OVER THE NEXT 24 HOURS AS THE
PRIMARY STEERING INFLUENCE TRANSITIONS FROM THE NER TO THE SOUTH TO
A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. AFTER THE STR BEGINS TO
DOMINATE, THE TRACK WILL SHIFT TO BE NORTHWESTWARD FOR THE REMAINDER
OF THE PERIOD. AFTER TAU 48, VWS IS EXPECTED TO BECOME MORE
FAVORABLE FOR INTENSIFICATION AND TS 18W IS EXPECTED TO BEGIN TO
GRADUALLY INTENSIFY, REACHING 40 KTS BY TAU 72. AS EXPECTED WITH A
COMPLEX STEERING ENVIRONMENT, DYNAMIC MODEL GUIDANCE IS IN POOR
AGREEMENT AS THEY DIFFER ON WHEN THE STR WILL TAKE OVER AS THE
DOMINANT STEERING INFLUENCE AND ON THE STRENGTH AND POSITION OF THE
RIDGE WHEN THAT HAPPENS. THE JTWC FORECAST TRACK CLOSELY FOLLOWS THE
MULTI-MODEL CONSENSUS, WHICH IS CONSISTENT WITH TRACKS FROM ECMWF,
COAMPS-GFS, AND JGSM. BASED ON THE HIGH UNCERTAINTY IN THE GUIDANCE,
THERE IS LOW CONFIDENCE IN THE FORECAST TRACK.
C. AFTER TAU 96, TS 18W IS EXPECTED TO ROUND THE STR AXIS AND
BEGIN TO RECURVE TOWARDS A NORTHEASTWARD TRACK WHILE SLOWLY
INTENSIFYING TO 45 KTS BY TAU 120. DYNAMIC MODEL GUIDANCE REMAINS IN
POOR AGREEMENT WITH THREE TRACK GROUPINGS AMONG THE NINE MEMBERS.
NAVGEM, UKMET, AND GALWEM BUILD THE STR TO THE NORTH MORE STRONGLY
AND FAVOR A SOUTHERN TRACK TOWARD OKINAWA. ECMWF, JGSM, AND COAMPS-
GFS CLOSELY FOLLOW THE JTWC FORECAST AND BRING THE SYSTEM FURTHER
NORTH AND AROUND THE STR AXIS BY THE END OF THE PERIOD. MEANWHILE,
GFS, THE GFS ENSEMBLE MEAN, AND HWRF DO NOT BUILD THE STR AS FAR TO
THE WEST OF THE CYCLONE AND PORTRAY A NORTH-NORTHWESTWARD TRACK OVER
SOUTHERN JAPAN. THE JTWC FORECAST TRACK LIES NEAR THE CONSENSUS
WHICH IS CLOSE TO THE ECMWF, COAMPS-GFS, AND JGSM SOLUTION. THE
INTENSITY FORECAST LIES NEAR THE CONSENSUS OF THE GUIDANCE WHICH IS
CLOSELY GROUPED WITH ONE EXCEPTION. COAMPS-GFS, WHICH IS AMONG THE
MEMBERS IN THE SOUTHERN TRACK GROUPING, HAS A PEAK INTENSITY OF 65
KTS. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST
BECAUSE OF THE WIDE SPREAD AMONG THE CONSENSUS MEMBERS.//
NNNN

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WDPN32 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (YAGI) WARNING NR
11//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 18W (YAGI), LOCATED APPROXIMATELY 458 NM SOUTHEAST
OF KADENA AB, HAS TRACKED SOUTHWESTWARD AT 07 KNOTS OVER THE PAST
SIX HOURS. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED
ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) WHICH DEPICTS A
LOW LEVEL CIRCULATION CENTER TUCKING UNDER RECENTLY FLARING
CONVECTION, THOUGH THE CENTER IS OBSCURED BY THIS CONVECTION. THE
INITIAL INTENSITY OF 35 KNOTS IS SLIGHTLY ABOVE THE PGTW AND RJTD
DVORAK CURRENT INTENSITY ESTIMATES OF T2.0 (30 KTS), BASED ON THE
LLCC TUCKING UNDER THE CONVECTION. UPPER-LEVEL ANALYSIS REVEALS A
MARGINAL ENVIRONMENT WITH MODERATE TO STRONG (20-30 KT) VERTICAL
WIND SHEAR (VWS) OFFSET BY GOOD EQUATORWARD OUTFLOW. TS 18W HAS
MOVED SOUTHWESTWARD OVER THE PAST 6 HOURS.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 18W IS FORECAST TO TRACK TO THE NORTHWEST OVER THE NEXT 72
HOURS ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE TO THE
EAST. BETWEEN TAU 36 AND TAU 48, VWS IS EXPECTED TO LESSEN AND,
ALTHOUGH THE EQUATORWARD OUTFLOW WEAKENS, POLEWARD OUTFLOW IMPROVES.
THIS IS EXPECTED TO SUPPORT TS 18W GRADUALLY INTENSIFYING AND
ORGANIZING THROUGH THE REMAINDER OF THE PERIOD. DYNAMIC MODEL
GUIDANCE IS IN POOR AGREEMENT ON THE FORECAST TRACK DUE TO
DIFFERENCES IN THE STRENGTH AND LOCATION OF THE STR BETWEEN THE
MEMBERS, ALTHOUGH MODEL TRACKS HAVE CONVERGED, WITH THE MODEL
CONSENSUS PASSING OVER OKINAWA BETWEEN TAU 48-72. THE SOUTHERNMOST
MEMBERS NOW RUN BY ISHIGAKIJIMA ISLAND, WHILE THE NORTHERNMOST
MEMBERS PASS SOUTH OF AMAMI OSHIMA ISLAND. THE JTWC FORECAST TRACK
HAS BEEN ADJUSTED TO THE WEST AND CLOSELY FOLLOWS THE MULTI-MODEL
CONSENSUS. BASED ON THE HIGH UNCERTAINTY IN THE GUIDANCE, THERE IS
LOW CONFIDENCE IN THE FORECAST TRACK.
C. AFTER TAU 72, TS 18W IS EXPECTED TO BEGIN ROUNDING THE STR
AXIS AND TRACK NORTHEASTWARD OVER KOREA PRIOR TO TAU 120. THE SLOW
INTENSIFICATION TREND IS EXPECTED TO CONTINUE FOR THIS PERIOD,
REACHING 45 KTS BY TAU 96. THE TRACK FORECAST REMAINS HIGHLY
UNCERTAIN WITH MOST MEMBERS DEPICTING THE CYCLONE RECURVING AFTER
TAU 96 BUT VARYING WIDELY ON WHERE THE CYCLONE IS AT THAT TIME.
ECMWF AND NAVGEM ARE WEST OF THE MULTIMODEL CONSENSUS AT THIS TIME,
AND LAG BEHIND CONSENSUS IN PREDICTING THE NORTHEASTWARD
ACCELERATION AT TAU 120 AFTER THE SYSTEM RECURVES. GFS AND HWRF LIE
TO THE EAST OF MODEL CONSENSUS, PREDICTING A TIGHTER TURN. THE JTWC
FORECAST TRACK IS HEDGED TO THE EAST OF THE MODEL CONSENSUS, BETWEEN
CONSENSUS AND THE LAST FORECAST TRACK, AS THE OVERALL CONSENSUS
SHIFTED TO THE WEST IN THE LATEST MODEL RUN. COAMPS-TC MODELS
PREDICT 18W WILL EXCEED 60 KTS, BUT HWRF SHOWS A SLOWER
INTENSIFICATION PROCESS, WITH A PEAK OF 45 KTS AT TAU 120. OVERALL,
THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST BECAUSE OF THE
WIDE SPREAD AMONG THE CONSENSUS MEMBERS.//
NNNN

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WDPN32 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (YAGI) WARNING NR
13//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 18W (YAGI), LOCATED APPROXIMATELY 388 NM SOUTHEAST
OF KADENA AB, HAS TRACKED NORTH-NORTHEASTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON A FULLY EXPOSED LLCC EVIDENT IN ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY TO THE NORTHEAST OF AN AREA OF DEEP CONVECTION,
CONFIRMED BY A 091719Z AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY
IS ASSESSED AT 40 KNOTS AND IS HEDGED SLIGHTLY LOWER THAN THE PGTW
FIX INTENSITY ESTIMATE OF T3.0 (45 KTS), PRIMARILY BASED ON A
091239Z ASCAT-A SCATTEROMETER PASS, WHICH SHOWED AN AREA OF 35-40
KNOT WINDS IN THE SOUTHWESTERN AND SOUTHERN QUADRANTS. ENVIRONMENTAL
ANALYSIS REVEALS A MARGINAL ENVIRONMENT WITH MODERATE TO STRONG (20-
30 KT) VWS, WEAK SOUTHWESTWARD OUTFLOW AND NO POLEWARD OUTFLOW. SEA
SURFACE TEMPERATURES ARE VERY WARM (30 DEG CELSIUS), BUT OHC VALUES
ARE RELATIVELY LOW. TS YAGI HAS SPED UP OVER THE PAST SIX HOURS,
AFTER SPENDING ROUGHLY 18 HOURS IN A NEARLY QUASI-STATIONARY
POSITION, ALONG THE WESTERN PERIPHERY OF A DEEP-LAYER STR TO THE
NORTHEAST.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 18W IS FORECAST TO TRACK TO THE NORTHWEST OVER THE NEXT 72
HOURS ALONG THE WESTERN PERIPHERY OF THE STR TO THE NORTHEAST. SOME
SLIGHT FLATTENING OF THE TRACK IS EXPECTED AFTER TAU 12 AS THE RIDGE
BECOMES SLIGHTLY MORE ELONGATED EAST-WEST. THE SYSTEM WILL BEGIN TO
TURN SLIGHTLY MORE POLEWARD BY TAU 72, AS IT BEGINS TO TRACK TOWARDS
A DEVELOPING WEAKNESS IN THE STEERING RIDGE. INTENSITY IS FORECAST
TO REMAIN STEADY THROUGH TAU 48, AS VWS WILL REMAIN RELATIVELY HIGH
AND OUTFLOW WILL BE RESTRICTED TO THE SINGLE WESTWARD CHANNEL,
DURING THIS PERIOD. SLIGHT INTENSIFICATION IS EXPECTED AFTER TAU 48,
AS VWS DECEASES AND THE SYSTEM BEGINS TO TAP INTO A POLEWARD OUTFLOW
CHANNEL AHEAD OF A DEEP MID-LATITUDE TROUGH APPROACHING FROM THE
WEST. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE FORECAST
TRACK TAU 36, WITH INCREASING SPREAD THEREAFTER. THE JGSM AND COTC
TRACKERS REPRESENT THE SOUTHERN MOST OUTLIERS, TAKING THE SYSTEM
SOUTH OF KADENA AND TRACKING STRAIGHT INTO EASTERN CHINA. THE GFS
AND ITS ENSEMBLE ARE THE NORTHERN OUTLIERS, TRACKING WELL NORTH OF
KADENA AND MAKING LANDFALL NEAR THE DMZ. THE JTWC TRACK IS PLACED
NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 72, ALTHOUGH, WITH THE
LARGE SPREAD IN THE GUIDANCE, THERE IS OVERALL LOW CONFIDENCE IN THE
FORECAST TRACK.
C. BY TAU 72, TS 18W WILL BEGIN TO ROUND THE STR AXIS AND TRACK
NORTH, THEN NORTHEASTWARD, MAKING LANDFALL ALONG THE WEST COAST OF
NORTH KOREA NEAR TAU 100. BY TAU 120, THE SYSTEM IS EXPECTED TO
REEMERGE INTO THE SEA OF JAPAN AND THEN ACCELERATE NORTHEASTWARD.
THE SYSTEM IS FORECAST TO REACH PEAK INTENSITY AT TAU 96, IN THE
YELLOW SEA, AS STRONG POLEWARD OUTFLOW WILL OFFSET THE INCREASING
VWS AHEAD OF THE APPROACHING TROUGH. AFTER LANDFALL, LAND
INTERACTION WILL DECREASE THE INTENSITY AS THE SYSTEM CROSSES THE
KOREAN PENINSULA. TS YAGI WILL BEGIN TO UNDERGO EXTRATROPICAL
TRANSITION BY TAU 96 AS IT INTERACTS WITH THE MID-LATITUDE
WESTERLIES AND BEGINS TO EXHIBIT SOME TEMPERATURE ADVECTION. THE
TRACK FORECAST BEYOND TAU 72 REMAINS HIGHLY UNCERTAIN WITH MOST
MEMBERS DEPICTING RECURVATURE, BUT VARYING ON THE TIMING AND DEGREE
OF THE CURVE. THE GALWEM AND EGRR DEPICT 18W MAKING LANDFALL ON THE
SHANDONG PENINSULA AND THEN TRACKING WELL INLAND OVER NORTHEAST
CHINA, WHILE GFS AND ITS ENSEMBLE SHOW LANDFALL IN SOUTH KOREA. THE
JTWC FORECAST TRACK IS HEDGED SLIGHTLY WEST AND SOUTH OF THE
MULTIMODEL CONSENSUS. WITH THE HIGH DEGREE OF UNCERTAINTY IN THE
GUIDANCE, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
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