Advisories

WDPN31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 146.2E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 211 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 60 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 30W MAINTAINS A VERY IMPRESSIVE APPEARANCE IN ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) AS THE SOUTHERN SIDE OF THE
EYE MOVES OVER AGRIHAN. THE 40-NM WIDE EYE HAS BEEN AS WARM AS +20
DEGREES CELSIUS AND EXHIBITS THE STADIUM EFFECT, THOUGH THE EDGES
HAVE BECOME SLIGHTLY MORE RAGGED. AT LEAST FOUR DISTINCT
MESOVORTICES WERE OBSERVED IN THE EYE. THE COMPACT CENTRAL DENSE
OVERCAST (CDO) RETAINS A SMOOTH CIRRUS CANOPY AND RADIAL OUTFLOW
ALOFT. ONE OF THE MOST IMPRESSIVE MICROWAVE PASSES FOR THIS STORM
WAS THE 291326Z GMI PASS, WHICH DEPICTED A NEAR-ANNULAR STRUCTURE
AND A SOLID RING OF EXCEPTIONALLY LOW BRIGHTNESS TEMPERATURES
ASSOCIATED WITH EXTREMELY POTENT CONVECTION IN THE 89 GHZ CHANNEL.
THE SUBSEQUENT 300249Z GMI 89 GHZ IMAGE SHOWED A LESS INTENSE
STRUCTURE WITH BANDING ALONG THE WESTERN AND SOUTHERN PERIPHERY. IT
IS QUITE POSSIBLE THAT THE SYSTEM PEAKED ABOVE 130 KTS CLOSE TO
291500Z, WHEN THE STORM'S BEST SATELLITE PRESENTATION HAD BEEN
SUSTAINED OVER SEVERAL HOURS. STORM- AND TYPHOON-FORCE WINDS
CONTINUE TO OCCUPY AN UNUSUALLY LARGE PORTION OF THE CDO AS
INDICATED BY THE 292247Z ASCAT-B DATA. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN MSI.
IN INFRARED IMAGERY ENHANCED BY THE BD CURVE, A THICK RING OF THE
BLACK SHADE RECENTLY WRAPPED AROUND THE EYE, ALTHOUGH AVERAGE CDO
CLOUD TOP TEMPERATURES HAVE SLOWLY WARMED, A SIGN THAT ANY
WEAKENING IS LIKELY TO BE PROGRESSING SLOWLY. THEREFORE, THE
INITIAL INTENSITY IS HELD AT 125 KTS WITH MEDIUM CONFIDENCE, WHICH
IS SUPPORTED BY THE T6.5 DVORAK ESTIMATES FROM PGTW AND RJTD. THE
ENVIRONMENT REMAINS FAVORABLE, CHARACTERIZED BY OCEAN HEAT CONTENT
(OHC) VALUES NEAR 100 KJ PER CM2 AND LOW VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 29N 154E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS SATCON: 132 KTS AT 300345Z
   CIMSS ADT: 102 KTS AT 300600Z
   CIMSS AIDT: 132 KTS AT 300600Z
   CIMSS D-MINT: 131 KTS AT 292245Z
   CIMSS D-PRINT: 126 KTS AT 300600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE JTWC FORECAST TRACK NOW DEPICTS A
NORTHEASTWARD TURN AT TAU 24 FOLLOWED BY A DEFLECTION TOWARD THE
WEST-SOUTHWEST AT TAU 48, AND A FASTER, SHARPER POLEWARD TURN AT
TAU 96 AND TAU 120.

FORECAST DISCUSSION: TY 30W IS NOW ROUNDING THE SOUTHWESTERN
PERIPHERY OF THE STR, GRADUALLY TURNING POLEWARD, AND APPROACHING A
LARGE WEAKNESS IN THE STR. A PROGRESSIVE LONGWAVE TROUGH PRESENTLY
PASSING OVER HONSHU IS RESPONSIBLE FOR THIS WEAKNESS, WHICH SHOULD
PERSIST THROUGH TAU 48. THE FORWARD MOTION WILL DECREASE, AND THE
VORTEX SHOULD BEGIN TO TURN NORTHEASTWARD. HOWEVER, THE TROUGH IS
UNLIKELY TO BE DEEP ENOUGH TO INITIATE A FULL RECURVATURE INTO THE
MID-LATITUDE WESTERLIES. INSTEAD, THE TROUGH WILL PASS QUICKLY BY
TAU 60, AND A SEPARATE STR TO THE WEST WILL BUILD EASTWARD, CLOSE
THE WEAKNESS, AND DEFLECT TY 30W SHARPLY WEST-SOUTHWESTWARD BETWEEN
TAU 36 AND TAU 72. AFTER TAU 72, A SECOND TROUGH WILL PASS OVER
HONSHU, CREATING ANOTHER OPENING IN THE STR AND GIVING TY 30W A
SECOND CHANCE TO TURN POLEWARD AND ESCAPE INTO THE WESTERLY FLOW.
CONFIDENCE IN THE FORECAST TRACK BEYOND TAU 24 IS VERY LOW BECAUSE
THE TRACK HINGES ON THE INTERACTION BETWEEN THE LONGWAVE TROUGH AND
THE STR, AS WELL AS THE PRECISE STORM LOCATION AS THE TROUGH RACES
EASTWARD.

VWS WILL REMAIN LOW THROUGH TAU 36. TY 30W IS LIKELY TO BE SLOWLY
WEAKENING BECAUSE IT HAS MOVED OFF A PATCH OF HIGHER OHC. HOWEVER,
IT IS QUICKLY APPROACHING ANOTHER AREA OF HIGHER OHC. THE INTENSITY
TREND SHOULD LEVEL OFF FROM TAU 12 TO TAU 24 AS A RESULT. TWO
DETRIMENTAL FACTORS ARISE THEREAFTER. THE SYSTEM WILL SLOW DOWN
SIGNIFICANTLY AS IT EXECUTES THE LOOP, WHICH MAY CAUSE UPWELLING OF
COOL WATER. SECOND, THE PASSAGE OF THE TROUGH TO THE NORTH WILL
BRIEFLY INDUCE MODERATE TO HIGH MID-LEVEL NORTHERLY SHEAR.
THEREFORE, THE FORECAST CALLS FOR STEADY WEAKENING FROM TAU 24 TO
TAU 60. AFTER THAT TIME, THE SYSTEM SHOULD GAIN MORE FORWARD SPEED,
AND VWS WILL EASE. THE LOOPING MOTION WILL OCCUR ALONG A SHARP
GRADIENT OF OHC, WITH SIGNIFICANTLY HIGHER VALUES TO THE SOUTH.
THIS FORECAST BRINGS THE VORTEX OVER LOWER OHC. THEREFORE, THE
FORECAST CALLS FOR A STABLE INTENSITY RATHER THAN REINTENSIFICATION
FROM TAU 60 TO TAU 72 AS THE SYSTEM GAINS MORE FORWARD SPEED AND
MOVES AWAY FROM THE UPWELLED WATER. BEYOND TAU 72, GRADUAL
WEAKENING IS PREDICTED AS OHC DROPS TO NEAR ZERO AND VWS ASSOCIATED
WITH THE SOUTHERN PERIPHERY OF THE JET STREAM INCREASES.

MODEL DISCUSSION: TRACK GUIDANCE AGREEMENT IS EXCELLENT THROUGH TAU
12 AND POOR FROM TAU 24 TO TAU 120. PREVIOUSLY, THE BULK OF THE
DYNAMICAL MODELS FAVORED A SHARP WESTWARD TURN FOLLOWED BY A
SECOND, GRADUAL RECURVATURE INTO THE WESTERLIES. THE AI MODELS HAVE
PERSISTENTLY DEPICTED A NORTHEASTWARD TURN PRIOR TO DEFLECTING
WESTWARD. THE OVERALL GUIDANCE IS GRADUALLY TRENDING TOWARD THE AI
SOLUTIONS, INCREASING CONFIDENCE IN THE SCENARIO DEPICTED BY THE AI
MODELS. CONSEQUENTLY, THE JTWC FORECAST TRACK HAS BEEN
SIGNIFICANTLY CHANGED BEYOND TAU 36 TO REFLECT THE MORE PROBABLE
SCENARIO. THIS TRACK IS PLACED AT THE CENTER OF THE TIGHT GUIDANCE
ENVELOPE AT TAU 12 AND THEN HEDGES TOWARD THE AI-MODEL MEAN (AICN).
BECAUSE HAFS-A AND UKMET ARE THE WESTERNMOST OUTLIERS FOLLOWING THE
SHARP WESTWARD TURN, THEY PULL THE JTWC MULTI-MODEL CONSENSUS
(CONW) WESTWARD. THE JTWC FORECAST TRACK THEREFORE LEANS AWAY FROM
CONW AFTER TAU 24. GOOGLE DEEPMIND AND ECMWF PREDICT A MORE
PROLONGED NORTHEASTWARD TRACK, FOLLOWED BY AN EVEN SHARPER LOOP AND
SUBSEQUENT RECURVATURE INTO THE WESTERLY FLOW, THAN THE JTWC
FORECAST. SUBSEQUENT FORECASTS MAY NEED TO SHOW A GREATER DISTANCE
TRAVELED IN THE NORTHEASTWARD DIRECTION AND A SHARPER SUBSEQUENT
RECURVATURE INTO THE WESTERLY FLOW.

SOME SPREAD EXISTS AMONG THE INTENSITY GUIDANCE, ALTHOUGH DEEPMIND,
COAMPS-TC, AND GFS FORM A CORE GROUP THAT SHOWS GRADUAL TO STEADY
WEAKENING THROUGH TAU 60, A PERIOD OF LITTLE INTENSITY CHANGE FROM
TAU 60 TO TAU 72, AND FURTHER WEAKENING BEYOND TAU 72. HAFS-A,
BEING THE WESTERNMOST OUTLIER, IS THE ONLY SOLUTION DEPICTING
REINTENSIFICATION AFTER THE SYSTEM MOVES AWAY FROM THE UPWELLED
WATERS. THE JTWC INTENSITY FORECAST LIES NEAR THE HIGH END OF THE
GUIDANCE ENVELOPE THROUGH TAU 36 BUT THEN LEANS MORE STRONGLY
TOWARD A SCENARIO OF MORE PERSISTENT WEAKENING THAN THE PREVIOUS
FORECAST, WHICH HELD THE INTENSITY STEADY IN THE LATTER PORTION OF
THE FORECAST PERIOD. THE INTENSITY FORECAST WILL DEPEND HEAVILY ON
THE EVENTUAL TRACK AND IS THEREFORE ASSESSED WITH LOW CONFIDENCE.

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