Advisories

WDPN31 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 042//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.2N 139.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 123 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION REFORMING NEAR THE LOW-LEVEL CIRCULATION CENTER (LLCC).
THE LLCC HAD BEEN ALMOST FULLY EXPOSED, AND THE REDEVELOPING
CONVECTION INDICATES THAT THE RECENT WEAKENING TREND MAY BE
REVERSING. ADDITIONALLY, THE POLEWARD OUTFLOW CHANNEL BETWEEN THE
SYSTEM AND THE JET STREAM TO THE NORTH IS STRENGTHENING. THE
200-850 MB ANALYZED SHEAR IS BELOW 10 KTS, WHILE THE MID-LEVEL
SHEAR IS CLOSER TO 20 KTS. THE ENVIRONMENT IS GENERALLY FAVORABLE,
CHARACTERIZED BY MODERATE SHEAR, WARMER SEA SURFACE TEMPERATURES
(SST) OF 27-28 DEGREES CELSIUS AS THE VORTEX MOVES AWAY FROM ITS
COLD WAKE, AND MODERATE TO STRONG DIVERGENCE ALOFT. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE TIGHTLY CURVED
BANDING IN EIR. THE INITIAL INTENSITY IS HELD AT 65 KTS WITH MEDIUM
CONFIDENCE. THIS ASSESSMENT LIES AT THE HIGH END OF THE CIMSS
OBJECTIVE ESTIMATES AND ACCOUNTS FOR THE RECENT REDEVELOPMENT OF
DEEP CONVECTION. ADT AND THE SUBJECTIVE DVORAK CLASSIFICATIONS ARE
ASSESSED TO BE TOO LOW BECAUSE THEY TEND TO UNDERESTIMATE INTENSITY
WHEN DEEP CONVECTION IS LACKING.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT
CHARACTERIZED BY A DEEP-LAYER STR TO THE WEST AND ANOTHER
DEEP-LAYER STR TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 63 KTS AT 021615Z
   CIMSS ADT: 34 KTS AT 021730Z
   CIMSS AIDT: 66 KTS AT 021730Z
   CIMSS D-MINT: 51 KTS AT 021641Z
   CIMSS D-PRINT: 52 KTS AT 021730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TY 30W IS CURRENTLY LOCATED INSIDE A COL
REGION BETWEEN TWO RIDGES. DURING THE PAST 12 HOURS, THE COMPETING
STEERING FLOW HAS RESULTED IN A SLOW NORTHWESTWARD MOTION AS THE
WEAKNESS IN THE RIDGE SHIFTED WESTWARD. THE SYSTEM IS BEGINNING TO
TURN POLEWARD AS A MID-LEVEL SHORTWAVE TROUGH ERODES THE RIDGE TO
THE WEST. THE STR TO THE EAST WILL BECOME THE MORE DOMINANT
STEERING MECHANISM, AND THUS THE SYSTEM WILL TURN POLEWARD OVER THE
NEXT 36 HOURS. TY 30W WILL BE POLEWARD OF THE RIDGE AXIS NEAR THAT
TIME AND WILL ACCELERATE NORTHEASTWARD BEYOND TAU 36. MODERATE
MID-LEVEL SHEAR WILL PERSIST THROUGH TAU 36. THE SYSTEM HAS MOVED
AWAY FROM THE COLD WAKE GENERATED BY THE LOOPING MOTION OVER THE
PAST FEW DAYS. WITH WATERS WARMER THAN 27 DEGREES CELSIUS AND
ENHANCED POLEWARD OUTFLOW PREDICTED TO CONTINUE, TY 30W WILL LIKELY
INTENSIFY. BEYOND TAU 36, THE SYSTEM WILL TRAVERSE PROGRESSIVELY
COOLER WATERS, AND VERTICAL WIND SHEAR WILL STEADILY INCREASE.
THESE FACTORS SHOULD RESULT IN WEAKENING THROUGH TAU 96. BAROCLINIC
INSTABILITY WILL INCREASE NEAR TAU 96, AND TY 30W SHOULD BEGIN
EXTRATROPICAL TRANSITION. THE FORECAST CALLS FOR BAROCLINIC
INTENSIFICATION TO A TYPHOON-FORCE EXTRATROPICAL CYCLONE BY TAU
120.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
48. THEREAFTER, THE CROSS-TRACK SPREAD REMAINS LOW, BUT THE
ALONG-TRACK SPREAD DRASTICALLY INCREASES, REACHING 870 NM AT TAU
120. GOOGLE DEEPMIND AND UKMET ARE THE FASTEST SOLUTIONS, WHILE
NAVGEM AND HWRF ARE THE SLOWEST. ECMWF AND GFS LIE IN BETWEEN AND
ARE MUCH CLOSER TO DEEPMIND THAN NAVGEM. THE JTWC FORECAST TRACK IS
POSITIONED NEAR THE AI-MODEL MEAN (AICN) THROUGH TAU 48 AND THEN
GRADUALLY LEANS AWAY FROM AICN TOWARD ECMWF AND GFS BY THE END OF
THE FORECAST PERIOD. THE INTENSITY GUIDANCE EXHIBITS MODERATE
SPREAD. THE DYNAMICAL MODELS PREDICT INTENSIFICATION THROUGH TAU
36, WHEREAS GOOGLE DEEPMIND LARGELY KEEPS THE INTENSITY FLAT.
HAFS-A AND COAMPS-TC DEPICT A PEAK OF 70 KTS AND 85 KTS,
RESPECTIVELY. BASED ON TRENDS IN THE SATELLITE PRESENTATION AND ON
THE GENERALLY FAVORABLE ENVIRONMENT AHEAD, THE JTWC INTENSITY
FORECAST CALLS FOR MODEST INTENSIFICATION THROUGH TAU 36, FOLLOWED
BY WEAKENING THROUGH TAU 72. DEEPMIND AND HAFS-A KEEP THE INTENSITY
UNCHANGED FROM TAU 72 TO TAU 92, WHILE GFS AND ECMWF BRING THE
SYSTEM BACK UP TO TYPHOON INTENSITY. THE JTWC INTENSITY FORECAST IS
CONSISTENT WITH THE LATTER DEPICTION.

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