482
WTPA44 PHFO 041504
TCDCP4
TROPICAL STORM GUILLERMO DISCUSSION NUMBER 23
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP092015
500 AM HST TUE AUG 04 2015
THE LATEST INFRARED SATELLITE PRESENTATION OF GUILLERMO HAS
DEGRADED IN APPEARANCE SINCE THE LAST ADVISORY...WITH WARMING CLOUD
TOPS AND A REDUCTION IN THE THUNDERSTORM ACTIVITY. THE LATEST
UW-CIMSS VERTICAL WIND SHEAR ANALYSIS INDICATES 25 KNOTS OF SHEAR
FROM 270 DEGREES...AND THIS IS LIKELY RESPONSIBLE FOR THE DEEP
CONVECTION HAVING DIFFICULTY MAINTAINING ITSELF NEAR THE LOW LEVEL
CIRCULATION CENTER OF GUILLERMO. DESPITE THE VERTICAL WIND SHEAR
PRESENT OVER THE SYSTEM...DVORAK CLASSIFICATIONS FROM PHFO AND JTWC
CONTINUE TO INDICATE T NUMBERS OF 3.5 OR 55 KNOTS...AND 3.0 OR 45
KNOTS FROM SAB. ADVANCED DVORAK TECHNIQUE (ADT) ALSO INDICATES A T
NUMBER OF 3.6 OR 57 KNOTS AS OF 04/1300Z. THE FINAL DECISION ON THE
INITIAL INTENSITY WAS ONCE AGAIN BASED ON DATA FROM THE U.S. 53RD
WEATHER RECONNAISSANCE AIRCRAFT WHICH SAMPLED THE INNER CORE OF
GUILLERMO EARLIER THIS MORNING. THE AIRCRAFT FOUND MAX FLIGHT LEVEL
WINDS OF 73 KNOTS...25 NM EAST OF THE CENTER OF CIRCULATION.
ADJUSTING THE FLIGHT LEVEL WINDS FROM THE 850 MB FLIGHT
LEVEL...YIELDS SURFACE WINDS OF 58 KNOTS. ADDITIONALLY...SFMR DATA
FROM THE AIRCRAFT INDICATED SURFACE WINDS OF AROUND 60 KNOTS IN THE
NE AND NW QUADRANTS OF THE STORM. AS A RESULT...THE INITIAL
INTENSITY OF GUILLERMO WAS KEPT JUST BELOW HURRICANE STRENGTH AT 60
KNOTS...UTILIZING A BLEND OF THE FLIGHT LEVEL AND SFMR WINDS FROM
THE AIRCRAFT.
THE INITIAL POSITION OF THE SYSTEM WAS BASED ON SATELLITE
EXTRAPOLATION FROM EARLIER CENTER FIX POSITIONS FROM THE
RECONNAISSANCE AIRCRAFT...WITH AN INITIAL MOTION TOWARD THE
NORTHWEST...OR 320 DEGREES AT 10 KNOTS. THE LATEST MODEL GUIDANCE
CHANGED VERY LITTLE FROM THE PREVIOUS ADVISORY PACKAGE...LIKELY
RESULTING FROM BETTER INITIALIZATION OF THE MOTION OF THE SYSTEM.
THE MOTION OF GUILLERMO APPEARS TO BE DRIVEN LARGELY BY THE
STRENGTH OF THE VERTICAL WIND SHEAR AS WELL AS A WEAKNESS IN THE
MID-UPPER LEVEL RIDGE WHICH EXTENDS FROM GUILLERMO OFF TO THE
NORTHWEST TO A LOCATION NEAR 30N157W. THE WEAKNESS IN THE RIDGE IN
COMBINATION WITH THE DEEP LAYER FLOW IS KEEPING GUILLERMO ON A TRACK
OFF TO THE NORTHWEST AT THE CURRENT TIME. AS A RESULT...THE OFFICIAL
FORECAST FOLLOWS A DIRECTION ON THE NORTH SIDE OF THE GUIDANCE
ENVELOPE THROUGH 24 HOURS WHICH ASSUMES MAINTENANCE OF DEEP
CONVECTION AND INTERACTION WITH THE WEAKNESS IN THE MID-UPPER LEVEL
RIDGE. BEYOND 24 HOURS AS WESTERLY WIND SHEAR IS FORECAST TO
INCREASE SIGNIFICANTLY OVER THE SYSTEM...CONVECTION SHOULD BECOME
INCREASINGLY SHALLOW...AND THE OFFICIAL FORECAST SHOWS A SHIFT
TOWARD THE WEST-NORTHWEST WHICH IS VERY CLOSE TO THE GFS AND TVCN
TRACKS AND SLIGHTLY TO THE NORTH OF THE PREVIOUS OFFICIAL FORECAST.
ON THIS TRACK...THE CLOSEST APPROACH OF GUILLERMO REMAINS WELL TO
THE NORTHEAST OF ALL THE HAWAIIAN ISLANDS. THE TROPICAL STORM WATCH
FOR THE BIG ISLAND AND MAUI COUNTY WAS MAINTAINED WITH THIS
ADVISORY PACKAGE...BUT IF THE MOTION OF THE SYSTEM CONTINUES...THE
WATCHES MAY BE CANCELLED LATER TODAY.
THE INTENSITY FORECAST FOR GUILLERMO IS A BLEND OF ICON AND HWRF
INTENSITY GUIDANCE ALONG WITH WEIGHT GIVEN TO THE PREVIOUS OFFICIAL
FORECAST. THE GLOBAL MODELS ARE SHOWING THE POTENTIAL FOR SOME
SLIGHT STRENGTHENING THROUGH THIS EVENING...AS SHEAR REMAINS NEARLY
UNCHANGED. VERTICAL WIND SHEAR IS THEN FORECAST TO FURTHER
STRENGTHEN OVER THE SYSTEM TONIGHT...AND THIS SHOULD LEAD TO STEADY
WEAKENING OF GUILLERMO THROUGH THE REMAINDER OF THE FORECAST. GIVEN
THE FAVORABLE SEA SURFACE TEMPERATURES OF AROUND 82 DEGREES
FAHRENHEIT BASED ON MODIS DATA FROM YESTERDAY AFTERNOON...IT IS NOT
OUT OF THE QUESTION THAT GUILLERMO COULD BECOME A HURRICANE OVER
THE NEXT 12 HOURS. THE OFFICIAL INTENSITY FORECAST WILL SHOW LITTLE
CHANGE IN STRENGTH HOWEVER OVER THE NEXT 12 HOURS...THEN SHOW SLOW
BUT STEADY WEAKENING THROUGH 120 HOURS.
ANOTHER RECONNAISSANCE AIRCRAFT MISSION INTO GUILLERMO IS SCHEDULED
FOR 18Z THIS MORNING. THE VALUABLE DATA TRANSMITTED IN REAL-TIME
FROM THESE MISSIONS WILL HELP US TO BETTER DETERMINE THE
LOCATION...INTENSITY AND SIZE OF THE TROPICAL STORM...ALONG WITH
ANY POTENTIAL IMPACTS TO THE HAWAIIAN ISLANDS.
FORECAST POSITIONS AND MAX WINDS
INIT 04/1500Z 19.7N 148.5W 60 KT 70 MPH
12H 05/0000Z 20.4N 149.6W 60 KT 70 MPH
24H 05/1200Z 21.4N 151.5W 50 KT 60 MPH
36H 06/0000Z 22.4N 153.4W 45 KT 50 MPH
48H 06/1200Z 23.1N 155.1W 40 KT 45 MPH
72H 07/1200Z 25.0N 159.0W 35 KT 40 MPH
96H 08/1200Z 26.5N 163.0W 30 KT 35 MPH
120H 09/1200Z 28.0N 167.0W 25 KT 30 MPH
$$
FORECASTER JELSEMA/BIRCHARD
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