Advisories

WDPN31 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8N 147.8E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 194 NM NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 65 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
30W AS A STILL ROBUST -- BUT WEAKENING -- ANNULAR CYCLONE. THE
CLOUD TOP TEMPERATURES WITHIN THE SOUTHERN QUADRANT HAVE WARMED TO
APPROXIMATELY -60C, INDICATING A WEAKENING TREND. ADDITIONALLY, THE
EYE DIAMETER HAS REDUCED TO 35 NM, AND THE CENTRAL TEMPERATURE HAS
WARMED BY APPROXIMATELY 5C. THE 292003Z WSFM MICROWAVE IMAGERY
SUGGESTS THE ANNULAR STRUCTURE MAY BE FALTERING, WITH THE ONCE
NEAR-PERFECT DONUT STRUCTURE OF THE STORM NOW SLIGHTLY DEGRADED.
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 LARGE,
CLEAR EYE. THE INITIAL INTENSITY OF 125 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A COMBINATION OF THE AGENCY DVORAK FIXES AND
CIMSS AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 292247Z ASCAT

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: 135 KTS AT 292230Z
   CIMSS ADT: 115 KTS AT 292330Z
   CIMSS AIDT: 132 KTS AT 300030Z
   CIMSS D-MINT: 131 KTS AT 292245Z
   CIMSS D-PRINT: 142 KTS AT 292330Z

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: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 30W (IN-FA) IS FORECAST TO CONTINUE
TRACKING WEST-NORTHWESTWARD THROUGH TAU 12 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, 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, EXPERIMENTAL AI MODELS) DEPICT 30W TRACKING 
NORTHEASTWARD BETWEEN TAU 24-60, BEFORE LOOPING BACK TO THE WEST. 
ALTERNATIVELY, OTHER RELIABLE MODEL GUIDANCE (GFS, NAVGEM, HWRF, 
UKMET, HAFS-A) DEPICTS A QUICK CHECKMARK TO THE SOUTHWEST, VICE A 
NORTHEASTWARD TRACK OR A QUASI-STATIONARY PERIOD. THOUGH NEITHER 
SCENARIO IS DEPICTED IN THE JTWC FORECAST, THEY ARE BOTH DISTINCT 
POSSIBILITIES 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 24, 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. ADDITIONALLY, VWS IS EXPECTED TO INCREASE
UPWARDS OF 25 KTS, CONTRIBUTING TO WEAKENING AND FORCING DRY AIR
INTO THE CORE. CONSEQUENTLY, 30W IS FORECAST TO STEADILY WEAKEN
BETWEEN TAU 36-60. THE LOCATION WHERE 30W BECOMES QUASI-STATIONARY 
HAS A SIGNIFICANT IMPACT ON THE POTENTIAL FOR UPWELLING, AS THAT 
REGION IS A SHARP GRADIENT BETWEEN HIGHER AND LOWER OHC VALUES. JUST 
EQUATORWARD OF THE FORECASTED TAU 36-60 IS A PATCH OF GOOD (100-125 
KJ PER CM SQUARED) OHC. SHOULD IN-FA TRACK FARTHER SOUTH THAN 
EXPECTED, THE WEAKENING EFFECTS FROM UPWELLING COULD BE LESS 
IMPACTFUL THAN FORECAST. CONVERSELY, A REGION OF MUCH LOWER (25-50 
KJ PER CM SQUARED) OHC EXISTS JUST POLEWARD OF THE TAU 36-60 
FORECAST POINTS. SO, 30W TRACKING FARTHER POLEWARD (OR TAKING THE 
NORTHEASTWARD TRACK INDICATED IN SOME MODEL GUIDANCE) COULD WEAKEN 
THE STORM MORE SIGNIFICANTLY. FOLLOWING TAU 60, 30W IS EXPECTED TO 
GENERALLY MAINTAIN INTENSITY ONCE MORE, AS THE ENVIRONMENT IS ABLE 
TO SUSTAIN A STABLE INTENSITY. THOUGH, AGAIN, THE INTENSITY TREND 
FOLLOWING TAU 60 GREATLY DEPENDS ON THE LATITUDE AT WHICH 30W BEGINS 
TRACKING WESTWARD.

MODEL DISCUSSION: DETERMINISTIC GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 24, 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,
AND THE EXPERIMENTAL AI MODELS, 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 MEAN, 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//
NNNN