Good read from the forecaster -
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
http://www.prh.noaa.gov/cphc/tcpages/arc...1508301456
