WTPA43 PHFO 301456

TCDCP3



HURRICANE IGNACIO DISCUSSION NUMBER  23

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP122015

500 AM HST SUN AUG 30 2015



THE SATELLITE PRESENTATION OF IGNACIO HAS DEFINITELY DEGRADED SINCE

THE LAST ADVISORY...WITH A RAGGED 20 NM WIDE EYE BECOMING

INTERMITTENTLY CLOUD-FILLED AND THE DEEP CONVECTIVE CANOPY BECOMING

NOTICEABLY SLIMMER ESPECIALLY ACROSS THE WEST AND SOUTHWEST

QUADRANTS. HOWEVER...SYSTEM SYMMETRY APPEARS TO HAVE RECOVERED A BIT

SINCE 1200 UTC. ALL THREE SATELLITE CENTERS DERIVED SUBJECTIVE

DVORAK SATELLITE INTENSITY ESTIMATES OF 6.0...115 KT...LIKE LAST

TIME. THE DIFFERENCE IS THAT ALL THESE ESTIMATES HAVE LOWER FINAL T

NUMBERS...DENOTING A WEAKENING TREND. UW-CIMSS ADT WAS 5.8 AT 1200

UTC...110 KT. IGNACIO INTENSITY LIKELY PEAKED 6 TO 10 HOURS AGO AND

EVERYTHING SHOWS A WEAKENING SYSTEM NOW. HOWEVER...SINCE WEATHER

RECONNAISSANCE AIRCRAFT SFMR SHOWED INTENSITY OF ABOUT 125 KT LAST

EVENING...WE WILL ASSIGN AN INITIAL INTENSITY OF 120 KT FOR THIS

ADVISORY...LOWER THAN LAST TIME BUT CONTINUED HIGHER THAN SATELLITE

ESTIMATES ALONE. WEATHER RECONNAISSANCE AIRCRAFT WILL FLY ONCE AGAIN

IN TIME FOR THE 1800 UTC ANALYSIS CYCLE.



THE SUSPECTED MORE NORTHERLY SHORT-TERM MOTION NOTED LAST TIME HAS

PERSISTED LONG ENOUGH TO BECOME OFFICIAL 12 HOUR MOTION...WHICH IS

NOW 330 DEGREES AT 8 KT. THE STEERING MECHANISM IS THE SAME...WITH A

WEAKNESS IN THE MID-LEVEL RIDGE EAST OF HAWAII ALLOWING IGNACIO TO

SLIDE NORTH NORTHWESTWARD. TRACK GUIDANCE CONTINUES TO BE TIGHTLY

PACKED DEPICTING LITTLE CHANGE FROM LAST TIME. HOWEVER...THE

GUIDANCE ENVELOPE WIDENED SLIGHTLY AS HWRF SHIFTED RIGHT WHILE GFDL

SHIFTED LEFT. THE FORECAST TRACK WAS SHIFTED TO THE RIGHT THROUGH 48

HOURS TO ACCOUNT FOR THE RECENT SWING TO NORTH NORTHWEST MOTION. THE

REMAINING FORECAST TRACK CLOSELY FITS THE LAST ONE...REMAINING NEAR

THE LEFT EDGE OF THE GUIDANCE ENVELOPE AND CLOSELY FOLLOWING GFS.

THIS FORECAST TRACK CHANGE DECREASES 34 KT WIND ONSET PROBABILITIES

FOR LOCATIONS WITHIN TROPICAL STORM WATCHES...BUT ENOUGH FORECAST

UNCERTAINTY PERSISTS TO KEEP THESE WATCHES UP FOR NOW. A SMALL

SYSTEM MOTION CHANGE BACK TO THE NORTHWEST OR WEST NORTHWEST COULD

GREATLY INCREASE THESE PROBABILITIES.



SATELLITE LOOP SHOWS IGNACIO IS UNDERGOING INCREASING STRESS DUE TO

VERTICAL SHEAR. OUTFLOW REMAINS HINDERED TO THE NORTHWEST AND THE

DEEP CONVECTIVE CANOPY EROSION NOTED SINCE LAST EVENING IS

CONSISTENT WITH WEST TO WEST SOUTHWEST SHEAR. SHIPS INTENSITY

GUIDANCE SHOWS 10 TO 15 KT OF SHEAR NOW...WITH SHEAR IN EXCESS OF 20

KT FORECAST FROM 24 HOURS ONWARD. THIS LIKELY EXPLAINS SHIPS

DIMINISHING IGNACIO TO TROPICAL STORM STATUS BY 48 HOURS. IN

CONTRAST...GLOBAL MODELS AND GFDL KEEP THIS SYSTEM QUITE STRONG

THROUGH THE NEXT FIVE DAYS...WITH LITTLE WEAKENING. HWRF WEAKENS

IGNACIO...BUT NOT AS FAST AS SHIPS. OUR FORECAST CALLS FOR GRADUAL

WEAKENING...MAKING IGNACIO A TROPICAL STORM ON DAY FIVE...AS A BLEND

WITH SHIPS AND HWRF.



THE NEED FOR TROPICAL STORM WATCHES FOR THE BIG ISLAND AND THE

ISLANDS OF MAUI COUNTY WILL BE RE-EXAMINED ONCE AIRCRAFT DATA

BECOMES AVAILABLE LATER THIS MORNING.



FORECAST POSITIONS AND MAX WINDS



INIT  30/1500Z 18.3N 148.4W  120 KT 140 MPH

 12H  31/0000Z 19.1N 149.1W  110 KT 125 MPH

 24H  31/1200Z 20.3N 150.5W  100 KT 115 MPH

 36H  01/0000Z 21.4N 152.0W   90 KT 105 MPH

 48H  01/1200Z 22.4N 153.6W   80 KT  90 MPH

 72H  02/1200Z 24.3N 156.6W   70 KT  80 MPH

 96H  03/1200Z 26.5N 159.9W   65 KT  75 MPH

120H  04/1200Z 28.7N 163.0W   60 KT  70 MPH



$$

FORECASTER POWELL