Advisories

WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 050//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.1N 138.5E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 198 NM WEST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON 
(TY) 30W (IN-FA) WITH A PARTIALLY EXPOSED LOW LEVEL CIRCULATION 
CENTER (LLCC) SLIGHTLY OFFSET TO THE WEST OF THE UPPER LEVEL 
CIRCULATION CENTER AS THE CONVECTION CONTINUES TO BE SHEARED TO THE 
EAST. A 041549Z AMSR-3 SUITE REVEALED THE MICROWAVE EYE FEATURE IN 
THE 37 GHZ IMAGE TO NOW BE ERODED IN THE SOUTHWESTERN QUADRANT WHILE 
THE 89 GHZ IMAGE CONFIRMED THE MAJORITY OF DEEP CONVECTION TO BE 
LOCATED POLEWARD AND EASTWARD OF THE LLCC. ENVIRONMENTAL CONDITIONS 
ARE ASSESSED AS MARGINALLY UNFAVORABLE, WITH HIGH (30-35 KTS) 
VERTICAL WIND SHEAR (VWS) CAUSING DRY AIR ENTRAINMENT ON THE WESTERN 
FLANK, OFFSET ONLY SLIGHTLY BY BORDERLINE (26-27 C) SEA SURFACE 
TEMPERATURES (SSTS) AND STRONG POLEWARD OUTFLOW. THE INITIAL POSITION 
IS PLACED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC 
AND EXTRAPOLATION FROM THE AMSR-3 IMAGERY. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE, IN LINE WITH THE CI VALUES OF AGENCY 
DVORAK FIXES, SLIGHTLY ABOVE CIMSS OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 73 KTS AT 041620Z
   CIMSS ADT: 72 KTS AT 041420Z
   CIMSS AIDT: 73 KTS AT 041420Z
   CIMSS D-MINT: 63 KTS AT 041621Z
   CIMSS D-PRINT: 63 KTS AT 041700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 30W IS FORECAST TO BEGIN A NORTHEASTWARD TURN 
IMMINENTLY AS IT ROUNDS THE SUBTROPICAL RIDGE (STR) CENTERED TO THE 
SOUTHEAST, ACCOMPANIED BY AN ACCELERATION IN TRACK SPEED.  
EXTRATROPICAL TRANSITION (ETT) IS EXPECTED TO BEGIN AT TAU 12 AS 30W 
NEARS THE BAROCLINIC ZONE AND BEGINS GAINING FRONTAL CHARACTERISTICS, 
WITH COMPLETION OF ETT EXPECTED NO LATER THAN TAU 36, AT WHICH POINT 
30W WILL BE FULLY EMBEDDED BENEATH THE STRONG UPPER-LEVEL WESTERLIES.
REGARDING INTENSITY, A STEADY WEAKENING TREND IS FORECAST FOR THE 
REMAINDER OF THE FORECAST PERIOD AS 30W CROSSES THE 26 C ISOTHERM 
AFTER TAU 12 AND VWS WILL INCREASE TO OVER 50 KTS BY TAU 36. THE WIND 
FIELD OF 30W IS EXPECTED TO EXPAND AND REMAIN RELATIVELY STRONG, 
FORECAST TO BE JUST BELOW TYPHOON INTENSITY AT THE TIME IT COMPLETES 
ETT.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD WITH THE EXCEPTION OF GALWEM WHICH 
TURNS 30W NORTHWARD AT TAU 24, DEVIATING FROM THE OTHERWISE TIGHT 
AGREEMENT ON A NORTHEASTWARD TRACK. ALONG-TRACK SPREAD IS THE LARGER 
AREA OF DISAGREEMENT, WITH THE EXPERIMENTAL AI MODEL WEATHER MESH 
LAGGING BEHIND, CAUSING AN ALONG-TRACK SPREAD OF 425 NM AT TAU 36. 
HOWEVER, DISREGARDING WEATHER MESH, HAFS-A, AND NAVGEM, THE REMAINDER 
OF MODELS ARE IN MUCH BETTER AGREEMENT, WITH AN ALONG-TRACK SPREAD OF 
175 NM AT TAU 36 AND ALL MODELS IN GOOD AGREEMENT ON TRACK SPEED OUT 
TO TAU 24. THE OFFICIAL JTWC FORECAST TRACK IS THUS LAID WITH HIGH 
CONFIDENCE, IN GOOD AGREEMENT WITH THE MULTI-MODEL AND AI CONSENSUS, 
FAVORING THE SLIGHTLY FASTER SPEED OF AICN AT TAU 36. INTENSITY MODEL 
GUIDANCE IS IN FAIR AGREEMENT ON A STEADY WEAKENING TREND FOR THE 
REMAINDER OF THE FORECAST PERIOD. THE EXCEPTIONS ARE HAFS-A AND HWRF 
WHICH SHOW AN INITIAL PLATEAU, FOLLOWED BY HAFS-A AND GFS DEPICTING 
INTENSIFICATION AFTER TAU 12 AS ETT BEGINS. THE OFFICIAL JTWC 
FORECAST INTENSITY IS THUS ASSESSED WITH MEDIUM CONFIDENCE, IN LINE 
WITH THE MULTI-MODEL CONSENSUS, SLIGHTLY ABOVE COAMPS-TC AND BOTH 
GOOGLE DEEPMIND WHICH ALL PORTRAY A STEEPER DECLINE TO TAU 24 AND A 
PLATEAU THEREAFTER. 

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