WTPA43 PHFO 011440

TCDCP3



HURRICANE IGNACIO DISCUSSION NUMBER  31

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP122015

500 AM HST TUE SEP 01 2015



THE SHEARED CORE ASSUMPTION MADE WITH THE LAST ADVISORY WAS CORRECT.

HOWEVER...IT TURNS OUT THAT THE EARLIER CDO CLOUD SWIRL FAVORED BY

THE SATELLITE CENTERS AT 0600 UTC WAS MORE SHEARED TO THE NORTHEAST

OF THE LLCC THAN ANTICIPATED. THE CDO HAS NOW BEEN COMPLETELY

SHEARED AWAY AND REPLACED WITH A WARMER BANDING FEATURE ACROSS THE

WESTERN AND NORTHERN SEMICIRCLES. THIS IS A WEAKER SATELLITE

PRESENTATION THAN LAST TIME...AND WE ARE NOT SURPRISED BY THE LOWER

INTENSITY NUMBERS RECEIVED FROM THE SATELLITE CENTERS. SUBJECTIVE

DVORAK INTENSITY ESTIMATES WERE ALL 4.0...65 KT. UW-CIMSS ADT WAS

4.3...72 KT. GIVEN THE CONTINUED DEGRADED APPEARANCE OF THIS

SYSTEM...WE WILL ASSIGN AN INITIAL INTENSITY OF 70 KT FOR THIS

ADVISORY.



A WELL-PLACED 0744 UTC ASCAT PASS...RECEIVED TOO LATE TO HELP LAST

TIME...SHOWED THAT THE LLCC HAS MAINTAINED A STEADY MOTION OF 315/09

KT OVER THE PAST 12 HOURS. AN 0743 UTC AMSU PASS SEEMS TO CONFIRM

THIS AS WELL AS A REANALYZED 0432 UTC SSMI PASS...WHICH HAS SINCE

BEEN EDITED IN THE FIX RECORD. THE 0600 UTC BEST TRACK POSITION HAS

BEEN REANALYZED AND REBESTED AS WELL. TRACK GUIDANCE REMAINS TIGHTLY

PACKED CARRYING IGNACIO GENERALLY TOWARD THE NORTHWEST THROUGH DAY

FIVE...WITH A SLIGHT SWING TO A MORE NORTHERLY TRACK LATE IN THIS

FORECAST PERIOD. HOWEVER...ALMOST ALL GUIDANCE SHIFTED TO THE

LEFT...MAKING EVEN THE REANALYZED MOTION TOO FAR TO THE RIGHT TO

KEEP THE SHORT TERM FORECAST TRACK WITHIN THE GUIDANCE ENVELOPE. THE

FORECAST TRACK FOR THIS ADVISORY THEREFORE KEEPS ITS INITIAL BUMP TO

THE RIGHT OF GUIDANCE TO ACCOUNT FOR INITIAL MOTION...THEN IS

ALTERED TO THE LEFT JUST ENOUGH AFTER 24 HOURS TO BLEND BACK INTO

THE ENVELOPE TO FOLLOW THE CURVE OF CONSENSUS GUIDANCE. THESE TRACK

ADJUSTMENTS WILL LIKELY OCCUR FOR THE NEXT FEW ADVISORIES AS THE

GLOBAL MODELS AND CONSENSUS GRAPPLE WITH HOW IGNACIO WILL BE STEERED

BY THE HIGH TO ITS DISTANT NORTHEAST AND THE WEAK MID-LEVEL TROUGH

TO ITS NORTHWEST.



INTENSITY GUIDANCE CONTINUES TO FAVOR VERY SLOW WEAKENING THROUGH

DAY FIVE...WITH IGNACIO STILL A TROPICAL STORM AT THE END OF THIS

PERIOD. HOWEVER...IGNACIO SHOULD BE PASSING OVER 23 TO 24 DEGREE

CELSIUS WATER AND APPROACHING 40N LATITUDE BY THE END OF THE

FORECAST PERIOD...SO THIS SYSTEM MAY BEGIN TO LOSE TROPICAL

CHARACTERISTICS BY THEN AND START EXTRATROPICAL TRANSITION. SHEAR

ACTUALLY DECREASES ALONG THE TRACK...BELOW 20 KT BETWEEN 36 AND 72

HOURS...AND THIS MAY ACCOUNT FOR GUIDANCE DEPICTION OF A LONGER

SYSTEM LIFE. SHIPS GUIDANCE SHOWS THE INTENSITY CHANGE CONTRIBUTIONS

FOR SHEAR DIRECTION AND SHEAR MAGNITUDE ALMOST CANCELLING EACH OTHER

OUT THROUGH 96 HOURS. ANYWAY...WE WILL FOLLOW THE SLOW WEAKENING

TREND FROM THE LAST ADVISORY AFTER ADJUSTING FOR THE LOWER INITIAL

INTENSITY.



FORECAST POSITIONS AND MAX WINDS



INIT  01/1500Z 23.5N 153.7W   70 KT  80 MPH

 12H  02/0000Z 24.4N 154.7W   65 KT  75 MPH

 24H  02/1200Z 25.5N 156.3W   65 KT  75 MPH

 36H  03/0000Z 26.5N 157.9W   65 KT  75 MPH

 48H  03/1200Z 27.6N 159.7W   60 KT  70 MPH

 72H  04/1200Z 30.6N 162.9W   60 KT  70 MPH

 96H  05/1200Z 34.2N 165.3W   60 KT  70 MPH

120H  06/1200Z 38.1N 167.2W   50 KT  60 MPH



$$

FORECASTER POWELL