Advisories

WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 30W (IN-FA) WARNING NR 
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1N 149.7E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 252 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 63 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SUPER
TYPHOON (STY) 30W (IN-FA) AS A HIGHLY COMPACT ANNULAR CYCLONE,
CHARACTERIZED BY THE LACK OF SPIRAL BANDS OF DEEP CONVECTION,
UNIFORM CLOUD TOPS, AND THE 'DONUT-LIKE' STRUCTURE OF THE STORM AS
DEPICTED IN THE 291325Z GMI MICROWAVE IMAGERY. THE LARGE,
SYMMETRICAL CENTRAL EYE REMAINS A DEFINING FEATURE, MAINTAINING AN
INTERNAL TEMPERATURE OF +21 C AND DIAMETER OF 43 NM. ENVIRONMENTAL
ANALYSIS REVEALS A HIGHLY FAVORABLE ENVIRONMENT, CHARACTERIZED BY
LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), WARM (28-29 C) SEA
SURFACE TEMPERATURES (SST), GOOD (100-125 KJ PER CM SQUARED) OCEAN
HEAT CONTENT (OHC), AND MODERATE RADIAL OUTFLOW. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE CLEAR EYE. THE
INITIAL INTENSITY OF 130 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGREEMENT BETWEEN THE AGENCY DVORAK FIXES AND CIMSS
AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF THE
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS SATCON: 146 KTS AT 291551Z
   CIMSS ADT: 117 KTS AT 291730Z
   CIMSS AIDT: 136 KTS AT 291730Z
   CIMSS D-MINT: 130 KTS AT 291552Z
   CIMSS D-PRINT: 134 KTS AT 291730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: ANNULAR CYCLONE

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: STY 30W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD THROUGH TAU 24 WHILE IT REMAINS ON THE
SOUTHWESTERN PERIPHERY OF THE STEERING STR. BETWEEN TAU 0-12, A
DEEP-LAYER TROUGH IS EXPECTED TO WEAKEN THE WESTERN FLANK OF THE
RIDGE, FORCING IT TO RETREAT TO THE EAST. 30W WILL APPROACH THE
RESULTING WEAKNESS AROUND TAU 24-36, CAUSING THE TRACK SPEEDS TO
SLOW SIGNIFICANTLY. SIMULTANEOUSLY, A SECOND STR CENTERED TO THE
WEST OF THE SYSTEM IS EXPECTED TO BUILD EASTWARD, INTRODUCING A
COMPETING STEERING ENVIRONMENT BETWEEN TAU 36-60. THE COMPETING
STEERING ENVIRONMENT COULD CAUSE 30W TO TRACK ERRATICALLY DURING
THAT TIME, INCLUDING BECOMING QUASI-STATIONARY, WHICH IS UNABLE TO
BE REFLECTED IN THE OFFICIAL FORECAST. A HANDFUL OF MODEL GUIDANCE
MEMBERS (ECMWF, GOOGLE DEEPMIND, GSM, NAVGEM, EXPERIMENTAL AI
MODELS) DEPICT 30W TRACKING NORTHEASTWARD BETWEEN TAU 36-60.
ALTERNATIVELY, OTHER RELIABLE MODEL GUIDANCE (HWRF, UKMET, HAFS-A)
DEPICT A QUICK CHECKMARK TO THE SOUTHWEST, VICE A NORTHEASTWARD
TRACK OR QUASI-STATIONARY PERIOD. THOUGH NEITHER SCENARIO IS
DEPICTED IN THE JTWC FORECAST, THEY ARE BOTH A DISTINCT POSSIBILITY
THAT COULD SIGNIFICANTLY ALTER THE FORECAST TRACK AFTER TAU 60.
AFTER TAU 60, THE STR POSITIONED TO THE WEST IS EXPECTED TO RETREAT
WESTWARD WHILE THE ORIGINAL STEERING RIDGE IS EXPECTED TO BUILD
WESTWARD. THE ORIGINAL STEERING RIDGE IS EXPECTED TO RETAIN
STEERING AUTHORITY AND CAUSE IN-FA TO TRACK NEARLY DUE WESTWARD
FROM TAU 60-96. AROUND TAU 96, AN UPPER-LEVEL TROUGH IS EXPECTED TO
PASS TO THE NORTH, ONCE AGAIN WEAKENING THE WESTERN FLANK OF THE
STR AND CONTRIBUTING TO A WEST-NORTHWESTWARD TRACK BETWEEN TAU
96-120. 

REGARDING INTENSITY, 30W IS EXPECTED TO GENERALLY MAINTAIN ITS
INTENSITY THROUGH TAU 36, WITH ONLY SLIGHT WEAKENING EXPECTED
DURING THAT TIME. THE ENVIRONMENT IS EXPECTED TO REMAIN HIGHLY
FAVORABLE AND IN-FA'S ANNULAR CHARACTERISTICS ARE EXPECTED TO AID
IN MAINTAINING INTENSITY. MINOR INTENSITY FLUCTUATIONS MAY BE
OBSERVED AS A RESULT OF UNPREDICTABLE STORM FORCES, WHICH CANNOT BE
REFLECTED IN THE OFFICIAL FORECAST. AFTER TAU 36, WHEN 30W ENTERS
THE COMPETING STEERING ENVIRONMENT, IN-FA IS EXPECTED TO BECOME
MORE SUSCEPTIBLE TO UPWELLING EFFECTS, AS THE OHC VALUES ARE
EXPECTED TO BE BETWEEN 50-75 KJ PER CM SQUARED WHEN THE STORM
STALLS BETWEEN RIDGES. CONSEQUENTLY, 30W IS FORECAST TO STEADILY
WEAKEN BETWEEN TAU 36-60. FOLLOWING TAU 60, 30W IS EXPECTED TO
GENERALLY MAINTAIN INTENSITY ONCE MORE, AS THE ENVIRONMENT IS ABLE
TO SUSTAIN A STABLE INTENSITY.

MODEL DISCUSSION: DETERMINISTIC GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36, BUT DIVERGES SIGNIFICANTLY THEREAFTER. AS DISCUSSED
ABOVE, A LARGE MODEL SPREAD EXISTS SURROUNDING THE COMPETING
STEERING ENVIRONMENT BETWEEN TAU 36-60. IF THE STORM TRACKS
NORTHEASTWARD BETWEEN TAU 36-60, AS DEPICTED BY ECMWF, DEEPMIND,
GSM, AND NAVGEM, THE TRACK FORECAST COULD SHIFT POLEWARD PAST TAU
60. HOWEVER, IF THE STEERING RIDGE REBUILDS WESTWARD QUICKLY AFTER
THE DEEP-LAYER TROUGH PASSES, 30W COULD CHECKMARK SHARPLY TO THE
SOUTHWEST, WHICH IS DEPICTED IN HAFS-A, HWRF, AND UKMET. IN THAT
SCENARIO, THE TRACK FORECAST COULD SHIFT EQUATORWARD AFTER TAU 60.
THE JTWC TRACK FORECAST LIES CLOSEST TO THE GEFS MENA, ECMWF,
EXPERIMENTAL WINDBORNE, AND THE AI MODEL CONSENSUS WITH OVERALL LOW
CONFIDENCE. 

RELIABLE INTENSITY AIDS ARE IN MODERATE AGREEMENT, WITH THE
MESOSCALE MODELS AND DEEPMIND DEPICTING A GRADUAL WEAKENING THROUGH
TAU 60 AND A RELATIVELY STABLE INTENSITY THEREAFTER. THE JTWC
INTENSITY FORECAST LIES SLIGHTLY HIGHER THAN THE BULK OF GUIDANCE
BETWEEN TAU 0-36, TO ACCOUNT FOR THE FAVORABLE ENVIRONMENTAL
CONDITIONS AND THE INTENSITY STABILITY TYPICALLY EXPECTED OF AN
ANNULAR CYCLONE. FOLLOWING TAU 36, THE JTWC INTENSITY FORECAST IS
IN DECENT AGREEMENT WITH THE MESOSCALE MODEL SOLUTIONS. THE TRACK
UNCERTAINTIES DISCUSSED ABOVE ALSO IMPACT INTENSITY UNCERTAINTY. A
POLEWARD SHIFT IN TRACK COULD RESULT IN FASTER THAN FORECAST
WEAKENING, WHILE AN EQUATORWARD SHIFT IN TRACK COULD HAVE THE
INVERSE EFFECT. AS A RESULT, THE JTWC INTENSITY FORECAST IS
ASSESSED WITH OVERALL 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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