Advisories

WDPN33 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.4N 156.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 854 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 
14W WITH A WELL-DEFINED AND FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER 
(LLCC) WITH FLARING CONVECTION CONFINED TO THE NORTHERN SEMICIRCLE. A 
072118Z F16 SSMIS 91 GHZ MICROWAVE IMAGE REVEALED LOW-LEVEL CLOUD 
LINES TIGHTLY WRAPPING INTO THE ASSESSED CENTER LARGELY UNOBSCURED BY 
DEEP CONVECTION. THE SYSTEM IS CURRENTLY PLACED ALONG THE NORTHEASTERN 
EXTENT OF A STRONG UPPER-LEVEL LOW, WHICH IS THE PRIMARY CULPRIT FOR 
THE LACK OF CONVECTION IN THE SOUTHERN SEMICIRCLE. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN 
ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES
LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 14W IS IN A
MARGINAL ENVIRONMENT CHARACTERIZED BY WEAK POLEWARD OUTFLOW, MODERATE 
SOUTHERLY VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE 
TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW TO
MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 35 KTS AT 080010Z
   CIMSS AIDT: 34 KTS AT 080010Z
   CIMSS D-MINT: 32 KTS AT 082302Z
   CIMSS D-PRINT: 32 KTS AT 080010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT FROM THE SOUTH

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 IS FORECAST TO TRACK
WEST-NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO THE NORTHEAST THROUGH TAU 24. NEAR TAU 24, A
STRONG UPPER-LEVEL TROUGH IS EXPECTED TO BREAK DOWN THE RIDGE AND
PUSH IT EASTWARD. THIS WILL CAUSE 14W TO BE PLACED WITHIN A WEAKER
STEERING ENVIRONMENT WHICH WILL CAUSE TRACK SPEEDS TO SLOW DOWN
WITH A NORTHWESTWARD TRAJECTORY. AROUND TAU 48, THE STEERING PATTERN 
WILL BECOME MORE DEFINED AS THE TROUGH PROPAGATES AWAY FROM THE SYSTEM 
AND RIDGING BUILDS IN TO THE NORTH. AS A RESULT, TRACK SPEEDS WILL 
ACCELERATE AND THE TRAJECTORY WILL TURN MORE WESTWARD AS 14W HEADS 
TOWARD NORTHERN HONSHU. LANDFALL IS CURRENTLY FORECAST TO OCCUR JUST 
AFTER TAU 72 NEAR SENDAI. THE VORTEX WILL THEN EMERGE WITHIN THE SEA 
OF JAPAN AROUND TAU 84 AS IT TRAVERSES WEST-SOUTHWESTWARD TOWARD THE 
KOREAN PENINSULA. THE SYSTEM ISFORECAST TO BEGIN SUBTROPICAL 
TRANSITION AT TAU 96 WITH COMPLETION BY TAU 120 AS A STRONG UPPER-
LEVEL LOW ANCHORS ITSELF OVER HONSHU, INDUCING VERY HIGH NORTHERLY 
VERTICAL WIND SHEAR OVER 14W, LIKELY CAUSING IT TO SHALLOW OUT AND 
DECOUPLE. IN TERMS OF INTENSITY, 14W IS FORECAST TO STEADILY INTENSIFY 
OVER THE NEXT 48 HOURS AS THE WIND FIELD BECOMES MORE SYMMETRIC AND 
OUTFLOW IMPROVES. AFTER TAU 48, SEA SURFACE TEMPERATURES BEGIN TO 
DROP, CAUSING 14W TO MAINTAIN AN INTENSITY OF ABOUT 50 KTS AS IT 
APPROACHES THE COAST. AFTER MAKING LANDFALL, TERRAIN INTERACTION AND 
SIGNIFICANTLY INCREASING NORTHERLY VERTICAL WIND SHEAR WILL CAUSE 14W 
TO WEAKEN AS IT TRAVERSES THROUGH THE SEA OF JAPAN.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT 
THROUGH OUT THE ENTIRE FORECAST PERIOD WITH THE EXCEPTION OF GALWEM, 
WHICH TRACKS THE VORTEX SIGNIFICANTLY FURTHER POLEWARD THAN THE 
REMAINDER OF GUIDANCE. DISCOUNTING GALWEM, THE CROSS-TRACK SPREAD AT 
TAU 72 IS ABOUT 120 NM AT TAU 72 WHICH IS MAINTAINED THROUGH TAU 120. 
THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MODIFIED CONSENSUS WITH 
HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. 
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT ON STEADY INTENSIFICATION 
THROUGH TAU 48 FOLLOWED BY A STEADY INTENSITY THROUGH TAU 72 FOLLOWED 
BY WEAKENING THROUGH TAU 120. PEAK INTENSITIES RANGE FROM 45 KTS TO 60 
KTS AT TAU 60-72. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE 
MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH OVERALL 
MEDIUM CONFIDENCE.

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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