Advisories

WDPN33 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.7N 162.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 315 NM SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS CURVED
BANDING WRAPPING INTO A RAGGED CENTRAL DENSE OVERCAST (CDO), WHICH
IS DISPLACED SOUTHWEST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC).
THIS COMPACT CIRCULATION HAS BEEN STRUGGLING TO CONSOLIDATE IN THE
FACE OF 15-20 KTS OF NORTHEASTERLY VERTICAL WIND SHEAR (VWS). WHILE
CLOUD TOP TEMPERATURES AS COLD AS -90 DEGREES CELSIUS HAVE BEEN
OBSERVED NEAR THE CENTER, THE CONVECTION HAS BEEN UNABLE TO FULLY
WRAP AROUND THE LLCC, INDICATING THAT THE VORTEX IS STILL
VERTICALLY MISALIGNED. A 070930Z ASCAT-B PASS INDICATES THAT THE
INTENSITY OF TROPICAL STORM (TS) 27W HAS BEEN OVERESTIMATED AND
SUGGESTS THAT THE INTENSITY MAY HAVE BEEN NEARLY STEADY OVER THE
PAST 30 HOURS. BASED ON THE ASCAT DATA, THE INITIAL INTENSITY HAS
BEEN SET AT 50 KTS WITH MEDIUM CONFIDENCE, WHICH LIES BETWEEN THE
T3.5-4.0 DVORAK CLASSIFICATIONS AND THE OBJECTIVE ESTIMATES FROM
CIMSS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON EIR EXTRAPOLATION AND ASCAT DATA, SLIGHTLY NORTHEAST OF THE
MID-LEVEL CIRCULATION CENTER.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) POSITIONED FAR TO THE NORTH-NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 070930Z
   CIMSS ADT: 47 KTS AT 071150Z
   CIMSS AIDT: 42 KTS AT 071150Z
   CIMSS D-MINT: 42 KTS AT 070858Z
   CIMSS D-PRINT: 43 KTS AT 071150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND WESTWARD

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: TS 27W WILL MAINTAIN A WEST-NORTHWESTWARD
TRAJECTORY THROUGH TAU 60 ALONG THE SOUTHWESTERN FLANK OF A STR
POSITIONED FAR TO THE NORTH-NORTHEAST. OVER THE NEXT 24 HOURS, THE
RIDGE WILL AMPLIFY AND MIGRATE WESTWARD, INDUCING A SLIGHTLY FASTER
TRANSLATION SPEED. TYPHOON (TY) 15E, LOCATED APPROXIMATELY 630 NM
TO THE NORTH-NORTHWEST, WILL PRODUCE A WEAKNESS IN THE WESTERN
EXTENSION OF THE RIDGE TO THE NORTH. AS TS 27W APPROACHES THIS
WEAKNESS AROUND TAU 72, THE SYSTEM WILL GRADUALLY TURN POLEWARD AND
SLOW DOWN. THE PERSISTENT SHEAR AND STRUCTURAL ISSUES PLAGUING TS
27W WILL LIMIT INTENSIFICATION FOR THE FIRST 12 HOURS. VWS WILL
BEGIN EASING AFTER TAU 12, REACHING TO LESS THAN 10 KTS BY TAU 24,
AND PROVIDE THE SYSTEM AN OPPORTUNITY TO QUICKLY CONSOLIDATE AS IT
TRAVERSES VERY WARM SST AND VERY HIGH OCEAN HEAT CONTENT (OHC)
EXCEEDING 150 KJ PER CM2. THESE HIGHLY FAVORABLE CONDITIONS WILL
ENABLE THE COMPACT VORTEX TO UNDERGO RAPID INTENSIFICATION (RI)
AFTER TAU 12 TO A PEAK OF 120 KTS AT TAU 60. BY TAU 96 AND TAU 120,
THE SYSTEM WILL MOVE OVER LOWER OHC, WHICH WILL INITIATE A
WEAKENING TREND. COMPACT CIRCULATIONS HAVE THE POTENTIAL TO
INTENSIFY VERY AGGRESSIVELY, AND THE FORECAST RATE OF
INTENSIFICATION AND PEAK INTENSITY MAY BE CONSERVATIVE.

MODEL DISCUSSION: THE SPREAD AMONG THE TRACK GUIDANCE HAS INCREASED
THIS CYCLE, LARGELY DUE TO ECMWF DEPICTING THE FASTEST POLEWARD
MOTION AND RECURVATURE, WHILE GFS AND THE GEFS ENSEMBLE MEAN FAVOR
THE MOST WESTWARD TRACKS. STILL, THE MULTI-MODEL CONSENSUS (CONW),
THE AVERAGE OF THE AI MODELS, AND GOOGLE DEEPMIND COMPRISE THE CORE
GROUPING OF MODELS NEAR THE CENTER OF THE GUIDANCE ENVELOPE.
THEREFORE, THE JTWC FORECAST TRACK IS NEARLY IDENTICAL TO THE
PREVIOUS, WITH ADJUSTMENTS AT EACH TAU OF LESS THAN 10 NM. THE
INTENSITY AIDS HAVE NOT CHANGED SUBSTANTIALLY. RI AIDS CONTINUE TO
TRIGGER, AND HAFS-A INSISTS ON IMMEDIATE RI TO A PEAK OF 120 KTS BY
TAU 48. COAMPS-TC DEPICTS A HIGHER PEAK OF 135 KTS. GIVEN THE
CURRENT SATELLITE PRESENTATION, IMMEDIATE RI APPEARS UNLIKELY. THE
JTWC INTENSITY FORECAST THEREFORE DELAYS THE ONSET OF RI BY 12
HOURS, SET CLOSEST TO THE DEEPMIND SOLUTION, CALLING FOR A PEAK OF
120 KTS AT TAU 60 AND THEN FOLLOWING A SIMILAR WEAKENING TREND.
THIS FORECAST REMAINS NEAR THE UPPER END OF THE GUIDANCE ENVELOPE.

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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