Advisories

WDPN31 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.9N 154.6E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 493 NM NORTH OF OROLUK
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 53 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A STILL
QUASI-ANNULAR STRUCTURE WITH LIMITED BANDING OUTSIDE THE CENTRAL
DENSE OVERCAST, WITH A LARGE CLEAR EYE MAINTAINING APPROXIMATELY 40
NM DIAMETER. THE INNER CORE WAS CLEARLY DISRUPTED OVER THE LAST 12
HOURS BY LIGHT TO MODERATE NORTHEASTERLY VERTICAL SHEAR, WHICH
CAUSED PERIODIC BREAKS IN THE CONVECTIVE RING IN THE NORTHEAST
QUADRANT AND WEST-SKEWED CONVECTIVE ASYMMETRY. DEEP CONVECTION HAS
SINCE ROTATED BACK INTO THE UPSHEAR QUADRANTS, POTENTIALLY
BEGINNING TO REESTABLISH A MORE SYMMETRIC CORE STRUCTURE. THE
INITIAL INTENSITY IS SET AT 115 KT BASED ON A BLEND OF AGENCY
DVORAK INTENSITY ESTIMATES AND AUTOMATED INTENSITY ESTIMATES, WHICH
GENERALLY FELL OVER THE PAST SIX HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS ADT: 99 KTS AT 282330Z
   CIMSS AIDT: 102 KTS AT 282330Z
   CIMSS D-MINT: 118 KTS AT 282306Z
   CIMSS D-PRINT: 124 KTS AT 290000Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 30W (IN-FA) CONTINUES TO TRACK ON A
12-HOUR HEADING OF ABOUT 280 DEGREES ALONG THE SOUTHWESTERN
PERIPHERY OF A SUBTROPICAL RIDGE TO THE NORTHEAST. THIS GENERAL
MOTION IS EXPECTED TO CARRY IN-FA THROUGH THE NORTHERN MARIANA
ISLANDS IN 24 TO 36 HOURS. THE STORM'S INNER CORE APPEARS TO BE
UNDERGOING FLUCTUATIONS IN SYMMETRY AND OVERALL HEALTH AS IT FIGHTS
OFF LIGHT TO MODERATE NORTHEASTERLY VERTICAL SHEAR, WHICH HAS
CAUSED SOME SHORT-TERM WEAKENING. THE INTENSITY MAY CONTINUE TO
VACILLATE OVER THE SHORT TERM DUE TO INTERNAL VORTEX PROCESSES AS
THE STORM REMAINS WITHIN A GENERALLY FAVORABLE ENVIRONMENT. THE
CURRENT DOSE OF VERTICAL SHEAR IS EXPECTED TO DECREASE AFTER ABOUT
24 HOURS. THE JTWC FORECAST HOLDS THE INTENSITY STEADY FOR THE
FIRST 48 HOURS, AVERAGING THROUGH POTENTIAL FLUCTUATIONS. AFTER 48
HOURS, THE PASSAGE OF A LONGWAVE TROUGH OVER JAPAN WILL OPEN A
BREAK IN THE SUBTROPICAL RIDGE, DRAWING 30W NORTHWESTWARD OR
NORTHWARD DURING THE 48 TO 72 HOUR PERIOD. HOWEVER, THE OPENING IS
EXPECTED TO CLOSE QUICKLY AS THE TROUGH EXITS EASTWARD, USHERING IN
A NEW SUBTROPICAL RIDGE BEHIND IT TO THE NORTHWEST OF THE STORM,
BLOCKING ITS NORTHWARD PROGRESS. AN ABRUPT PIVOT BACK WESTWARD TO
THE SOUTH OF IWO TO IS FORECAST BY MOST DYNAMICAL AND AI-BASED
MODELS AFTER TAU 72, POTENTIALLY FOLLOWING A CLOCKWISE-SHAPED LOOP
IN THE TRACK. UNCERTAINTY IN BOTH TRACK AND INTENSITY GROWS DURING
AND AFTER THIS PIVOT DUE TO THE COMPLEX STEERING CURRENTS. THE
TYPHOON'S INTENSITY DURING THIS PERIOD WILL LIKELY BE GOVERNED
PRIMARILY BY OCEAN CONDITIONS, AS THE STORM'S SLOWING MOTION DURING
THE 48 TO 72 HOUR PERIOD MAY INDUCE COLD UPWELLING BENEATH THE
CIRCULATION, SUCH AS DEPICTED IN THE HAFS-A COUPLED MODEL. THE
MAGNITUDE OF THIS POTENTIAL COOLING IS UNCERTAIN, AS 30W WILL BE
TRACKING NEAR A TIGHT GRADIENT IN OCEAN HEAT CONTENT VALUES AROUND
THAT TIME. THE JTWC FORECAST SHOWS MODEST WEAKENING DURING TAU 48
TO 72. THEREAFTER, MODELS DISAGREE ON WHETHER A BROADENING STORM
STRUCTURE WILL CAUSE CONTINUED WEAKENING, OR WHETHER RENEWAL OF
WARM WATER BENEATH THE CIRCULATION WILL LEAD TO REINTENSIFICATION.
THE JTWC FORECAST SPLITS THE DIFFERENCE WITH A NEAR-STEADY
INTENSITY DURING THE 72 TO 120 HOUR PERIOD.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
CONW CONSENSUS OF A TIGHT CLUSTER OF MEMBERS THROUGH 60 HOURS,
AFTER WHICH SPREAD GROWS CONSIDERABLY DUE TO THE COMPLEX STEERING
ENVIRONMENT. DURING THE 72 TO 120 HOUR PERIOD, THE JTWC TRACK
FORECAST LEANS MORE TOWARD THE AI-BASED GUIDANCE. THE JTWC
INTENSITY FORECAST LOOSELY FOLLOWS A BLEND OF HAFS-A, HWRF, AND THE
GOOGLE DEEPMIND ENSEMBLE MEAN.

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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