WDPS31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07P (SEVEN) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3S 162.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 201 NM WEST-SOUTHWEST OF NOUMEA, NEW
CALEDONIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 27 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS TC 07P
(SEVEN) BEGINNING ITS SLOW DEMISE. THE CONVECTIVE STRUCTURE HAS
BEGUN TO SEPARATE INTO TWO DISTINCT REGIONS, ONE STRETCHING OUT
ALONG THE WEST COAST OF NEW CALEDONIA, AND THE OTHER, MORE
SYMMETRIC, REMAINING NEAR THE ASSESSED CENTER. A 071746Z SSMIS 89GHZ 
IMAGE SUPPORTS THIS ASSESSMENT, SHOWING WELL-DEFINED
CONVECTIVE BANDS WRAPPING INTO A MICROWAVE EYE FEATURE NEAR THE
ASSESSED CENTER POSITION, AND AN ELONGATED BAND OF LINEAR
CONVECTION TO THE NORTHEAST. WHILE THE STRUCTURE LOOKS IMPRESSIVE,
WITH THE MICROWAVE EYE, THE SYSTEM IS DEFINITELY STARTING TO FEEL
THE EFFECTS OF MODERATE NORTHWESTERLY SHEAR, CURRENTLY ESTIMATED BY
CIMSS TO BE AROUND 22 KNOTS, HENCE THE ELONGATION SEEN IN THE EIR.
THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
CONGRUENCE OF AGENCY FIX POSITIONS AND A SERIES OF MICROWAVE IMAGES
INDICATING A MICROWAVE EYE. THE INITIAL INTENSITY REMAINS SET AT 45
KNOTS WITH MEDIUM CONFIDENCE, AT THE AVERAGE OF SUBJECTIVE AND
OBJECTIVE FIXES. THE ENVIRONMENT IS BECOMING INCREASINGLY MARGINAL,
WITH INCREASING SHEAR AND DECREASING SSTS BEING OFFSET FOR THE TIME
BEING BY THE ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   NFFN: T2.5 - 35 KTS
   CIMSS SATCON: 51 KTS AT 071511Z
   CIMSS ADT: 49 KTS AT 071730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TC 07P LIKELY PEAKED IN INTENSITY OVERNIGHT,
AND WHILE STILL HOLDING ONTO THE PEAK INTENSITY FOR THE MOMENT,
WILL EMBARK ON A SLOW WEAKENING TREND GOING FORWARD. TC 07P IS
RACING SOUTHEASTWARD ALONG THE STRONG GRADIENT ON THE SOUTHWEST
SIDE OF THE STR, WITH CURRENT FORWARD SPEED ESTIMATED AT 27 KNOTS.
THE FORECAST IS EXPECTED TO TAKE TC 07P ON THE SOUTHEAST TRAJECTORY
THROUGH THE FORECAST PERIOD, BUT IT SHOULD START TO SLOW DOWN A BIT
AS THE STR STRETCHES OUT AND WEAKENS, REDUCING THE STEERING
GRADIENT. AS MENTIONED, THE SYSTEM HAS PEAKED IN INTENSITY AND WILL
START TO WEAKEN DUE PRIMARILY TO STEADILY INCREASING SHEAR. A DEEP
UPPER-LEVEL TROUGH COMING OFF THE COAST OF AUSTRALIA TODAY WILL
QUICKLY MOVE EASTWARD AND THE DRY MID-LEVEL AIR ASSOCIATED WITH
THIS SYSTEM WILL COMPLETELY ENGULF TC 07P BY TAU 24. THE COMBINED
EFFECTS OF THE DRY AIR AND HIGH SHEAR WILL DECAPITATE TC 07P BY
AROUND TAU 24, LEAVING BEHIND A GALE FORCE LOW-LEVEL CIRCULATION.
AT THE SAME TIME, THE SYSTEM WILL BEGIN SUBTROPICAL TRANSITION
(STT) BY TAU 12. BY TAU 36 THE SYSTEM WILL BE A FULLY SUBTROPICAL
LOW AS IT MOVES OVER COOL WATERS AND EMBEDS UNDER THE SUBTROPICAL
WESTERLIES. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
THE SHORT FORECAST PERIOD, WILL ALL MEMBERS OF THE CONSENSUS
CONSTRAINED WITHIN A VERY TIGHT ENVELOPE OF LESS THAN 75NM, LENDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS
ALSO IN GOOD AGREEMENT, WITH THE BULK OF THE GUIDANCE INDICATING A
SHORT PERIOD OF STEADY INTENSITY FOLLOWED BY STEADY WEAKENING
THROUGH TAU 36. THE JTWC FORECAST LIES ON TOP OF THE HWRF SOLUTION
WITH HIGH CONFIDENCE.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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