Advisories

WDPN33 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.7N 160.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 475 NM NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 14W AS A HIGHLY SHEARED AND FULLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) COMPLETELY DEVOID OF CONVECTION SAVE FOR
A PITIFUL PLUME OF CENTRAL CONVECTION WEAKLY EMANATING FROM THE
LLCC. DRY AIR IS SPIRALING INTO THE CORE FROM THE WEST AND SOUTH.
THE 070709 91 GHZ SSMIS PASS REVEALS THE LOW-LEVEL CLOUD BANDING
AND THE LACK OF DEEP CONVECTION. ADDITIONALLY, LARGE AMOUNTS OF
DRY AIR ARE ALSO PRESENT IN THE IMAGE. ENVIRONMENTAL ANALYSIS
REVEALS AN UNFAVORABLE ENVIRONMENT, CHARACTERIZED BY MODERATE TO
HIGH (20-25 KTS) VERTICAL WIND SHEAR (VWS), MARGINALLY WARM (26-27
C) SEA SURFACE TEMPERATURES (SST) AND VERY LOW OCEAN HEAT CONTENT,
WITH POOR OUTFLOW AND LARGE AMOUNTS OF DRY AIR. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE FULLY EXPOSED
LLCC. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE CIMSS AUTOMATED INTENSITY ESTIMATES AND THE
AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A WESTWARD
EXTENSION OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 070810Z
   CIMSS ADT: 45 KTS AT 070810Z
   CIMSS AIDT: 36 KTS AT 070810Z
   CIMSS D-MINT: 28 KTS AT 070708Z
   CIMSS D-PRINT: 27 KTS AT 070810Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT 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: TS 14W (CHAN-HOM) IS FORECAST TO CONTINUE
TRACKING NORTHWESTWARD WHILE IT REMAINS UNDER THE STEERING
INFLUENCE OF THE WEAK STR CENTERED TO ITS NORTHEAST. BETWEEN TAU
24-36, A DEEP TROUGH WILL WEAKEN THE RIDGE AND CAUSE 14W TO SLOW
TRACK SPEEDS AND TRACK DUE WESTWARD BETWEEN TAU 24-48. FOLLOWING
THE PASSAGE OF THE TROUGH AROUND TAU 48, THE STR WILL REBUILD AND
DRIVE 14W NORTHWESTWARD THROUGH TAU 96. TOWARDS THE END OF THE
FORECAST PERIOD, A SHALLOW STR OVER THE SEA OF JAPAN WILL BUILD AND
CAUSE 14W TO TRACK DUE WESTWARD AGAIN BETWEEN TAU 96-120. REGARDING
INTENSITY, 14W IS EXPECTED TO GRADUALLY INTENSIFY THROUGH TAU 72 AS
THE ENVIRONMENT SLOWLY BECOMES MORE FAVORABLE. VWS IS EXPECTED TO
EASE SLIGHTLY BY TAU 24 AND ALLOW FOR SLIGHT INTENSIFICATION.
HOWEVER, BY AROUND TAU 72, SSTS ARE EXPECTED TO BECOME UNFAVORABLE
AND INDUCE WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD.
14W IS FORECAST TO BEGIN SUBTROPICAL TRANSITION NO LATER THAN TAU
120.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 72, SUPPORTING THE JTWC TRACK WITH HIGH
CONFIDENCE. FOLLOWING TAU 72, TRACK GUIDANCE DIVERGES SIGNIFICANTLY
IN THE CROSS-TRACK DIRECTION, CAUSING UNCERTAINTY WITH THE
LATE-TERM TRACK FORECAST. THE JTWC TRACK FORECAST IS PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE FROM TAU 72-120.
RELIABLE INTENSITY AIDS ARE IN STRONG AGREEMENT THROUGHOUT THE
FORECAST, SUPPORTING THE JTWC INTENSITY FORECAST WITH HIGH
CONFIDENCE. 

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