Advisories

WDPN34 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (FIFTEEN) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.1N 160.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 570 NM NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
LOW LEVEL CIRCULATION CENTER (LLCC), OBSCURED BY PERSISTENT DEEP
CONVECTION. A 100547Z PARTIAL SSMIS 91GHZ MICROWAVE IMAGE REVEALED
STRONG CURVED BANDING FEATURES ALONG THE NORTH AND NORTHWEST FLANKS, 
CONSISTENT WITH THE CONVECTIVE SIGNATURE IN THE MSI. THE INITIAL 
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE CIMSS ARCHER 
FIX FROM THE SSMIS IMAGE AND THE JTWC MICROWAVE FIX. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE PHFO T2.5 
DVORAK CURRENT INTENSITY (CI) ESTIMATE AND A BLEND OF THE OBJECTIVE 
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE 
MARGINALLY UNFAVORABLE, WITH MODERATE POLEWARD OUTFLOW ALOFT AND WARM 
SSTS OFFSET BY MODERATE VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: EASTERN PERIPHERY OF A LARGE-SCALE
CYCLONIC GYRE CENTERED TO THE WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 38 KTS AT 100410Z
   CIMSS ADT: 32 KTS AT 100600Z
   CIMSS AIDT: 36 KTS AT 100600Z
   CIMSS D-MINT: 44 KTS AT 100631Z
   CIMSS D-PRINT: 41 KTS AT 100710Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EASTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST PERIOD HAS BEEN EXTENDED
TO 36 HOURS. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 15W (FIFTEEN) IS TRACKING
NORTH-NORTHEASTWARD ALONG THE EASTERN PERIPHERY OF AN EXPANSIVE
CYCLONIC GYRE CENTERED TO THE WEST. THE SYSTEM IS APPROACHING THE
LATITUDE WHERE THE GRADIENT FLOW AROUND THE GYRE IS WEAKEST, AND WILL 
BEGIN TO SLOW DOWN THROUGH THE FORECAST PERIOD. AS THE SYSTEM IS 
MOVING INTO THE NORTHEASTERN QUADRANT OF THE GYRE CIRCULATION, THERE 
IS A SIGNIFICANT AMOUNT OF UNCERTAINTY IN THE TRACK OF TS 15W. IT 
WILL EITHER EJECT NORTHEASTWARD OR TURN NORTHWESTWARD, CONTINUING ITS 
GENERAL CYCLONIC TRAJECTORY AROUND THE GYRE. THE FORECAST FOLLOWS THE 
FORMER SCENARIO, WITH TS 15W SLOWLY TRACKING NORTHEASTWARD THROUGH 
THE FORECAST PERIOD. IN TERMS OF INTENSITY, TS 15W HAS SHOWN 
CONSIDERABLE RESILIENCE OVER THE PAST DAY, WITH A SMALL POCKET OF 
DEEP CONVECTION PERSISTING OVER THE LLCC. A BURST OF STRONG 
SOUTHWESTERLY VWS, ACCOMPANIED BY DRY MID-LEVEL AIR ENTRAINMENT AND 
UPPER-LEVEL CONVERGENCE, WILL SHEAR THE DEEP CONVECTION FROM THE 
SYSTEM AFTER TAU 12, LEAVING BEHIND A SHALLOW VORTEX THAT WILL 
GRADUALLY WEAKEN THROUGH THE FORECAST PERIOD.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN POOR AGREEMENT, DIVERGING
FROM TAU 00 THROUGH THE END OF THE FORECAST PERIOD. NAVGEM, UKMET,
AND THE CONSENSUS MEAN TAKE THE SYSTEM ON THE CYCLONIC TRAJECTORY,
TURNING NORTHWESTWARD BY TAU 36. CONVERSELY, THE AI MODELS, AGFS AND 
HAFS-A DEPICT THE SYSTEM EJECTING OUT OF THE GYRE ON THE 
NORTHEASTWARD TRACK THROUGH THE END OF THE FORECAST. THE JTWC 
FORECAST IS PLACED NEAR THE AI CONSENSUS MEAN, WITH MEDIUM 
CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM 
WILL STEADILY WEAKEN AND DISSIPATE WITHIN 36 HOURS. 

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