WTPA41 PHFO 262050

TCDCP1



TROPICAL STORM NIALA DISCUSSION NUMBER   8

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP062015

1100 AM HST SAT SEP 26 2015



SSMIS PASSES AT 1640 UTC AND 1714 UTC...COMBINED WITH A SHORT

VISIBLE SATELLITE LOOP...CONFIRM THAT NIALA HAS MADE ITS EXPECTED

TURN TOWARD THE WEST...AND MAY HAVE BEGUN TO MAKE THIS TURN BEFORE

THE 1200 UTC SATELLITE ANALYSIS CYCLE. WHAT APPEARS TO BE THE

WESTERN EDGE OF THE LOW LEVEL CIRCULATION CENTER..LLCC...IS PEEKING

OUT FROM UNDER DEEP CONVECTION. WINDS AT NEARBY BUOY ONE HAVE BEGUN

TO BACK...POSSIBLY INDICATING THAT NIALA IS ON TRACK TO PASS SOUTH

OF IT. OVERALL SATELLITE PRESENTATION IS OF A SYSTEM UNDERGOING

HIGH AMOUNTS OF WEST SOUTHWESTERLY SHEAR...VARYING FROM 25

KT...ACCORDING TO SHIPS...TO 35 KT...ACCORDING TO UW-CIMSS. THE

SOLE OUTFLOW CHANNEL IS TO THE NORTHEAST. SUBJECTIVE SATELLITE

INTENSITY ESTIMATES RANGE FROM 3.5...55 KT...FROM PHFO AND SAB...TO

3.0...45 KT...FROM JTWC. UW-CIMSS ADT REPRESENTS THE HIGH END AT

4.0...65 KT. REANALYSIS OF SATELLITE AND MICROWAVE DATA SHOWS THAT

NIALA WAS LIKELY STRONGER THAN ASSIGNED 24 HOURS AGO...POSSIBLY

FLIRTING WITH HURRICANE STRENGTH THEN. OUR 55 KT INITIAL INTENSITY

FOR THIS FORECAST CYCLE REPRESENTS A WEAKENING FROM THAT PEAK

INTENSITY 24 HOURS AGO...AND IS NOT MEANT TO REPRESENT STRENGTHENING

OVER THE PAST 6 TO 12 HOURS. NIALA IS ON A WEAKENING TREND AND HAS

BEEN SINCE LATE FRIDAY.



INITIAL MOTION IS 270/06 KT...ALTHOUGH 12 HOUR MOTION STILL SHOWS A

CONSIDERABLE...AND NOW POSSIBLY UNREPRESENTATIVE...NORTHERLY

COMPONENT. A STRONG HIGH PRESSURE CENTER FAR NORTH OF HAWAII APPEARS

TO BE GAINING INFLUENCE OVER NIALA AT THE EXPENSE OF MID AND UPPER

TROUGHING EXTENDING FAR TO THE NORTHEAST OF HAWAII. THIS IS TO BE

EXPECTED AS DEEP CONVECTION IS INCREASINGLY SHEARED AWAY. TO ACCOUNT

FOR INITIAL MOTION...THE 12...24 AND 36 HOUR FORECAST POINTS WERE

ADJUSTED NOTICEABLY TO THE LEFT OF THE PREVIOUS FORECAST...WITH THE

REST OF THE TRACK CLOSELY ALIGNING WITH THE PREVIOUS ONE. THIS KEEPS

THE FINAL FORECAST TRACK WITHIN THE TIGHT CONSENSUS TRACK GUIDANCE

ENVELOPE...AND TAKES NIALA 120 TO 150 MILES SOUTH OF THE BIG ISLAND

BETWEEN 24 AND 48 HOURS. THE SHORT-TERM FORECAST TRACK SHIFT TO THE

LEFT NEGATED ANY EFFECT THE HIGHER INITIAL INTENSITY HAD ON 34 KT

WIND PROBABILITIES...SO THE TROPICAL STORM WATCH FOR THE BIG ISLAND

WILL CONTINUE UNCHANGED. IT IS VERY LATE IN THE FORECAST CYCLE

NOW...AND 2000 UTC GOES VISIBLE IMAGERY SHOWS OUR ALTERED INITIAL

POSITION MAY STILL BE A TENTH OF A DEGREE TOO FAR NORTH.



AGAIN...TROPICAL STORM NIALA LIKELY PEAKED NEAR HURRICANE STRENGTH

ABOUT 24 HOURS AGO AND HAS BEEN WEAKENING EVER SINCE. THIS TREND

WILL CONTINUE THROUGH THE NEXT FIVE DAYS IN THE FACE OF INCREASING

SHEAR...IN SPITE OF CONTINUED WARM SSTS. MOST INTENSITY GUIDANCE

WEAKENS NIALA VERY QUICKLY...WITH SHIPS ESSENTIALLY DISSIPATING THIS

SYSTEM BY 120 HOURS. THIS SEASON HAS HAD ITS SHARE OF RESILIENT

TROPICAL SYSTEMS...SO OUR FORECAST WEAKENING TREND IS NOT AS QUICK

AS MOST GUIDANCE. AFTER SLOWLY WEAKENING THROUGH 48 HOURS...WE

FORECAST NIALA WILL DEGRADE TO A POST-TROPICAL REMNANT LOW...BUT NOT

DISSIPATE...ON DAY FOUR.





FORECAST POSITIONS AND MAX WINDS



INIT  26/2100Z 17.1N 152.1W   55 KT  65 MPH

 12H  27/0600Z 17.1N 152.8W   50 KT  60 MPH

 24H  27/1800Z 17.1N 153.8W   45 KT  50 MPH

 36H  28/0600Z 16.9N 154.9W   45 KT  50 MPH

 48H  28/1800Z 16.7N 155.9W   40 KT  45 MPH

 72H  29/1800Z 16.1N 157.7W   30 KT  35 MPH

 96H  30/1800Z 15.5N 159.7W   25 KT  30 MPH...POST-TROP/REMNT LOW

120H  01/1800Z 14.8N 161.8W   25 KT  30 MPH...POST-TROP/REMNT LOW



$$

FORECASTER POWELL