Advisories

WDPN32 PGTW 110300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (PEILOU) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.4N 155.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 674 NM WEST-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 25 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DISORGANIZED
CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) OF
TROPICAL STORM (TS) 13W. A WEDGE OF DRY AIR TO THE WEST OF THE
SYSTEM CAN BE OBSERVED IN ANIMATED WATER VAPOR IMAGERY MAKING ITS
WAY INTO THE VORTEX CORE. SOME PRESSURE FROM SOUTHERLY VERTICAL
WIND SHEAR IS ALSO EVIDENT, DISPLACING THE REMAINING CONVECTION
SLIGHTLY NORTH OF THE ASSESSED CENTER. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON LOW-LEVEL CLOUD MOTION
BRIEFLY EXPOSED IN THE SOUTHEASTERN QUADRANT AND TRACKING
CONVECTIVE FEATURES IN ANIMATED MSI. THE INITIAL INTENSITY OF 35
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK
FIXES AND OVERALL LACK OF STRUCTURAL CHANGE IN THE ANIMATED MSI.
THE ENVIRONMENT IS CHARACTERIZED AS MARGINAL WITH WARM SEA SURFACE
TEMPERATURES AND LOW VERTICAL WIND SHEAR, OFFSET BY THE DRY AIR
ENTRAINMENT AND WEAK OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 53 KTS AT 110000Z
   CIMSS AIDT: 43 KTS AT 110000Z
   CIMSS D-PRINT: 45 KTS AT 110000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 13W (PEILOU) HAS ACCELERATED NORTHEASTWARD
OVER THE PAST 6 HOURS ON A TRACK THAT IS SEPARATING IT FROM THE
EASTERN PERIPHERY OF THE CYCLONIC GYRE CENTERED TO THE WEST. AN
EXTENSION OF A SUBTROPICAL RIDGE BUILDING IN SOUTH OF THE SYSTEM IS
HELPING TO MAINTAIN THE NORTHEASTWARD TRACK OVER THE NEXT 24 HOURS,
EVENTUALLY STEERING THE SYSTEM EAST-NORTHEASTWARD BY TAU 36. THE
INTENSITY IS EXPECTED TO STEADILY DECREASE FOR THE DURATION OF THE
FORECAST PERIOD AS DRY AIR CONTINUES TO INTRUDE INTO THE CORE, SEA
SURFACE TEMPERATURES DECREASE, AND WESTERLY VWS INCREASES.
DISSIPATION IS EXPECTED UNDER THESE UNFAVORABLE ENVIRONMENTAL
CONDITIONS BY TAU 36. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ABOUT
THE NORTHEASTWARD TRAJECTORY FOLLOWED BY AN EAST-NORTHEASTWARD TURN
BY TAU 36, WITH A CROSS-TRACK SPREAD OF 75 NM AT THAT TIME. THE
JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE. MODEL INTENSITY GUIDANCE IS ALSO IN AGREEMENT
ABOUT THE WEAKENING TREND OF 13W, WITH THE NOTABLE EXCEPTION OF THE
DECAY SHIPS SOLUTIONS, WHICH SUGGEST STEADY INTENSIFICATION. THIS
ABERRATION IS LIKELY DUT TO THE FACT THAT SHIPS LOSES TRACK OF THE
VORTEX AND REVERTS TO CLIMATOLOGY BASED SOLUTIONS. THE JTWC
INTENSITY FORECAST IS PLACED ON THE LOW END OF THE GUIDANCE
ENVELOPE WITH MEDIUM CONFIDENCE, DISCOUNTING THE SHIPS SOLUTIONS AS
OUTLIERS.

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