Advisories

WDPN31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8N 164.5E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 314 NM NORTHWEST OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
PERSISTENT VORTICAL HOT TOWERS ASSOCIATED WITH A SEEMINGLY RAGGED
CENTRAL DENSE OVERCAST (CDO). THE SYSTEM MAINTAINS A STRONG
CONNECTION TO A POLEWARD OUTFLOW CHANNEL FEEDING INTO AN
UPPER-LEVEL TROUGH WELL TO THE NORTHEAST, ALTHOUGH EQUATORWARD
VENTILATION IS SUPPRESSED. MODERATE MID-LEVEL SHEAR PERSISTS, WHICH
IS LIKELY A PRIMARY REASON FOR THE RAGGED NATURE OF THE CDO.
HOWEVER, THE VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30
DEGREES CELSIUS AND THE POLEWARD OUTFLOW CHANNEL HAVE STILL ENABLED
THE VORTEX TO INTENSIFY. IN FACT, A 250718Z SAR PASS BY RCM-2
INDICATED TYPHOON-FORCE WINDS SURROUNDING A 15-NM WIDE EYE, WHICH
IS NOT VISIBLE IN CONVENTIONAL SATELLITE IMAGERY. A 250709Z WSF-M
PASS ALSO REVEALED A LOWER-LEVEL EYE FEATURE THAT DOES NOT YET
EXTEND TO THE UPPER TROPOSPHERE. BASED ON THE SAR DATA AND THE
DVORAK CLASSIFICATIONS COMING IN AT T3.5-4.5, 30W HAS BEEN
DESIGNATED A 75-KT TYPHOON (TY) WITH MEDIUM CONFIDENCE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE VORTICAL HOT
TOWERS IN EIR IMAGERY, IN LINE WITH THE FIXES FROM PGTW AND PHFO.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A DEEP-LAYER
NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS ADT: 57 KTS AT 251140Z
   CIMSS AIDT: 48 KTS AT 251140Z
   CIMSS D-MINT: 67 KTS AT 250956Z
   CIMSS D-PRINT: 65 KTS AT 251110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 IS TRAVELING NORTH-NORTHWESTWARD ALONG
THE NORTHWESTERN PERIPHERY OF THE NER. OVER THE NEXT 48 HOURS, A
DEEP MID-LEVEL TROUGH WILL PASS OVER THE KOREAN PENINSULA AND
APPROACH HONSHU. THIS FEATURE WILL REORIENT THE SUBTROPICAL RIDGE
(STR) AND SHIFT IT EASTWARD, EVENTUALLY CONSOLIDATING NEARLY DUE
NORTH OF TY 30W. THEREFORE, TY 30W WILL GRADUALLY TURN WESTWARD AND
SLOW DOWN OVER THE NEXT 48 HOURS AS IT ENCOUNTERS DEEP-LAYER
EASTERLY FLOW ALONG THE SOUTHERN FLANK OF THE STR. THEREAFTER, THE
SYSTEM WILL ACCELERATE WESTWARD TO WEST-NORTHWESTWARD ALONG THE
SOUTHERN SIDE OF THE STR. BY TAU 120, TY 30W WILL REACH THE
SOUTHWESTERN FLANK OF THE RIDGE AND BEGIN TO TURN MORE POLEWARD.
DESPITE MODERATE MID-LEVEL SHEAR ENTRAINING DRY AIR INTO THE
VORTEX, THE SYSTEM HAS MANAGED TO STEADILY INTENSIFY. THE VERY
COMPACT CORE WILL LIKELY UNDERGO ADDITIONAL INTENSIFICATION,
POTENTIALLY RAPID UNDER SIMILAR CONDITIONS OF MODERATE SHEAR, VERY
WARM SST, AND ROBUST POLEWARD VENTILATION THROUGH TAU 24. AFTER
THAT TIME, THE UPPER-LEVEL TROUGH WILL TRAVEL WELL DOWNSTREAM, AND
THE POLEWARD OUTFLOW CHANNEL WILL SHUT OFF. ADDITIONALLY, THE
SLOWER MOTION FROM TAU 24 TO TAU 48 WILL INCREASE THE POTENTIAL FOR
UPWELLING OF COOLER SUBSURFACE WATERS. THEREFORE, THE FORECAST
HOLDS THE INTENSITY NEARLY STEADY DURING THIS TIME. A SECOND ROUND
OF INTENSIFICATION WILL BEGIN ONCE THE SYSTEM GAINS SUFFICIENT
FORWARD SPEED AND CONTINUES OVER VERY WARM SST.
DIFFICULT-TO-PREDICT INTERNAL TROPICAL CYCLONE DYNAMICS DURING THE
LATTER PART OF THE FORECAST PERIOD INTRODUCE ADDITIONAL INTENSITY
UNCERTAINTY, SO THE FORECAST HOLDS THE INTENSITY AT THE SAME LEVEL
AT TAU 96 AND TAU 120.

MODEL DISCUSSION: NEARLY ALL MODEL SOLUTIONS NOW DEPICT A WESTWARD
TURN OVER THE NEXT 48 HOURS. HWRF IS THE LONE OUTLIER, STILL
DEPICTING A SLIGHT EASTWARD TURN FOLLOWED BY A U-TURN TOWARD THE
WEST. COMPARED TO THE PREVIOUS CYCLE, THE ENTIRE GUIDANCE SUITE HAS
TIGHTENED, WITH DECREASING CROSS-TRACK AND ALONG-TRACK SPREAD. THE
MORE RELIABLE TRACK MODELS, INCLUDING GOOGLE DEEPMIND, ECMWF, AND
GFS, ALL LIE NEAR THE CENTER OF THE GUIDANCE ENVELOPE FROM TAU 48
TO TAU 120. THE JTWC FORECAST TRACK IS PLACED ALONG THIS TIGHT
CLUSTER OF MODELS, BASED ON A BLEND OF THE MULTI-MODEL CONSENSUS,
THE AI-MODEL MEAN, DEEPMIND, AND ECMWF. THIS SUPPORTS HIGH TRACK
CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER.
AGREEMENT AMONG THE INTENSITY GUIDANCE HAS IMPROVED, WITH DEEPMIND,
COAMPS-TC, AND HAFS-A SHOWING SIGNIFICANT NEAR-TERM
INTENSIFICATION. MANY RI AIDS HAVE TRIGGERED, PROVIDING ADDITIONAL
SUPPORT FOR SIGNIFICANT INTENSIFICATION. HAFS-A AND COAMPS-TC
INTENSIFY TY 30W TO 120-130 KTS BY TAU 36. AFTERWARD, HAFS-A
DEPICTS WEAKENING TO 100 KTS DUE TO UPWELLING, WHILE DEEPMIND AND
COAMPS-TC HOLD THE INTENSITY NEARLY STEADY. MODELS THEN DEPICT
STEADY INTENSIFICATION AFTER TAU 60 TO 125-130 KTS BY TAU 96. 70
PERCENT OF THE DEEPMIND ENSEMBLE MEMBERS ATTAIN SUPER TYPHOON
INTENSITY BY TAU 96. THE JTWC INTENSITY FORECAST IS SET NEAR, BUT
SLIGHTLY LOWER THAN, THE DEEPMIND SOLUTION THROUGH TAU 120.

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