Advisories

WDPN31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.8N 144.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 187 NM SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: 110 DEGREES AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
30W (IN-FA) WITH A COOLING EYE THAT HAS BECOME PARTIALLY CLOUD-FILLED 
AND RAGGED. A 312102Z MWI 89 GHZ MICROWAVE IMAGE DEPICTS THE 
MICROWAVE EYE TO BE ASYMMETRICAL IN APPEARANCE WITH THE REMNANTS OF 
THE PREVIOUS INNER EYEWALL STILL DISTINGUISHABLE ON THE NORTHERN SIDE 
ALIGNING WITH THE EYE FEATURE IN MSI, WHILE THE PRIMARY, FULLY INTACT 
EYEWALL EXTENDS FARTHER TO THE WEST AND REMAINS WEAKEST IN THE 
SOUTHWESTERN QUADRANT, WITH ROBUST BANDS EXTENDING OFF OF THE 
NORTHEASTERN QUADRANT. ENVIRONMENTAL CONDITIONS ARE ASSESSED AS 
MARGINALLY UNFAVORABLE AS STRONG POLEWARD OUTFLOW ALOFT AND LOW (10-
15 KTS) VERTICAL WIND SHEAR (VWS) ARE OFFSET BY THE UPWELLING OF 
COOLER (26-27 C) SEA SURFACE TEMPERATURES (SSTS) AND DRY AIR 
ENTRAINMENT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE 
BASED ON THE EYE FEATURE IN SATELLITE IMAGERY. DESPITE THE CENTRAL 
DENSE OVERCAST (CDO) DETERIORATING IN SYMMETRY AND SIZE, 30W HAS 
INTERMITTENTLY REGAINED COOLER SURROUNDING CLOUD TOPS OVER THE LAST 
SIX HOURS, RESULTING IN A SLIGHT OSCILLATION OF INTENSITY ESTIMATES. 
THE INITIAL INTENSITY IS THUS ASSESSED WITH MEDIUM CONFIDENCE BASED 
ON THE SPREAD OF AGENCY DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT IN A COL
BETWEEN TWO SUBTROPICAL RIDGES CENTERED TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 90 KTS AT 312158Z
   CIMSS ADT: 97 KTS AT 312330Z
   CIMSS AIDT: 88 KTS AT 312330Z
   CIMSS D-MINT: 89 KTS AT 312157Z
   CIMSS D-PRINT: 88 KTS AT 010000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: OCEANIC UPWELLING; DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 30W HAS LIKELY BEGUN ITS CLOCKWISE LOOP AS IT
STALLS IN TRACK SPEED WITHIN THE COL BETWEEN THE SUBTROPICAL RIDGES
(STRS) CENTERED TO THE EAST AND WEST OF THE SYSTEM. BY TAU 24, THE 
SYSTEM IS EXPECTED TO INCREASE SLIGHTLY IN TRACK SPEED AND PROCEED
WESTWARD AS THE STEERING RIDGE TRANSLATES WESTWARD AND THE STR TO
THE WEST BUILDS AN EASTWARD EXTENSION. BY TAU 48, A PASSING MID-
LATITUDE TROUGH WILL WEAKEN THE WESTERN STR AND ALLOW THE EASTERN STR 
TO REGAIN PRIMARY STEERING INFLUENCE, INDUCING A POLEWARD TURN BY TAU 
60 AND A NORTHEASTWARD TURN BY TAU 72. AT THIS TIME, TRACK SPEED WILL 
ALSO ACCELERATE, WITH EXTRATROPICAL TRANSITION (ETT) BEGINNING BY TAU 
96 AND COMPLETING BY TAU 120 AS 30W NEARS THE STRONG UPPER-LEVEL 
WESTERLIES AND BAROCLINIC ZONE. REGARDING INTENSITY, A WEAKENING 
TREND IS EXPECTED AS 30W REMAINS WITHIN THE WEAK STEERING ENVIRONMENT 
AND UPWELLS COOL SSTS. A PLATEAU IS EXPECTED FROM TAU 24 TO 72 AS 
TRACK SPEED INCREASES SLIGHTLY, ALLOWING 30W TO SKIRT ALONG AN AREA 
OF ROUGHLY 50 KJ PER CM SQUARED OCEAN HEAT CONTENT (OHC) AND VWS 
REMAINS RELATIVELY CONSISTENT. MODEST INTENSIFICATION IS POSSIBLE 
BETWEEN TAUS 48 AND 72 AS UPPER LEVEL OUTFLOW IS EXPECTED TO INCREASE 
AS 30W NEARS THE STR AXIS, BUT IS NOT REFLECTED IN THE OFFICIAL 
FORECAST. AFTER TAU 72, STEADY WEAKENING IS EXPECTED FOR THE 
REMAINDER OF THE FORECAST PERIOD AS OHC DECREASES, VWS SHARPLY 
INCREASES AND ENTRAINS FURTHER DRY AIR WITH THE ONSET OF ETT.

MODEL DISCUSSION: TRACK MODEL GUIDANCE HAS REMAINED FAIRLY CONSISTENT 
WITH THE PREVIOUS CYCLE OUT TO TAU 72, WITH CONTINUED WESTERN 
OUTLIERS OF UKMET, UKMET ENSEMBLE, AND GALWEM. DISREGARDING THESE, 
CROSS-TRACK SPREAD IS 145 NM AT TAU 72. BEYOND THIS POINT, TRACK 
SPEED CONTINUES TO GREATLY DIVERGE WITH THE MAJORITY OF AI-BASED 
MODELS, GFS, AND GFS-BASED COAMPS-TC ARE MUCH FASTER THAN THE 
REMAINING ECMWF, HAFS, GEFS, AND EXPERIMENTAL WEATHER MESH MAKING UP 
THE MIDDLE OF THE GROUPING, AND THE AFOREMENTIONED OUTLIERS ALSO 
BEING THE SLOWEST OF THE PACKAGE (PLUS JGSM). THE OFFICIAL JTWC 
FORECAST TRACK IS THUS PLACED WITH MEDIUM CONFIDENCE OUT TO TAU 72, 
IN LINE WITH THE AI CONSENSUS AND LOW CONFIDENCE THEREAFTER, CLOSER 
TO THE TRACK SPEED OF ECMWF, GEFS, AND WEATHER MESH. MODEL INTENSITY 
GUIDANCE IS IN FAIR AGREEMENT ON A SHORT TERM WEAKENING, BUT DIVERGE 
IN REGARD TO THE PLATEAU OR RE-INTENSIFICATION FROM TAUS 24 TO 72. 
HAFS-A HAS THE STRONGEST RE-INTENSIFICATION WHILE BOTH GOOGLE 
DEEPMINDS DEPICT MORE STEADY WEAKENING THROUGHOUT. MODELS AGREE ON 
STEADY WEAKENING AFTER TAU 72 AS ETT BEGINS. THE OFFICIAL JTWC 
FORECAST INTENSITY IS ASSESSED WITH LOW CONFIDENCE THROUGHOUT, IN 
AGREEMENT WITH COAMPS-TC AND THE MULTI-MODEL CONSENSUS.

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