WTPA41 PHFO 272057

TCDCP1



TROPICAL STORM NIALA DISCUSSION NUMBER  12

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP062015

1100 AM HST SUN SEP 27 2015



THE LOW LEVEL CIRCULATION CENTER...LLCC...HAS BECOME EXPOSED ONCE

AGAIN AFTER SPENDING MUCH OF THE NIGHT BENEATH THE SOUTHWEST EDGE

OF DEEP CONVECTION. THIS CONVECTION HAS SINCE DECREASED...WITH

THE HIGH LEVEL DEBRIS SHEARING OFF TO THE EAST. NEW DEEP CONVECTION

HAS FORMED ALONG THE NORTHERN FLANK OF THE LLCC...BUT HAS NOT

COMPLETELY OBSCURED IT YET AS OF 1930 UTC. FIX CONFIDENCE IS QUITE

HIGH...WITH ALL THREE SATELLITE CENTERS PLACING NIALA IN EXACTLY THE

SAME PLACE...TO THE TENTH OF A DEGREE ANYWAY. SUBJECTIVE DVORAK

INTENSITY ESTIMATES RANGE FROM 2.5...35 KT...FROM JTWC...TO 3.5...45

KT...FROM SAB AND PHFO. UW-CIMSS ADT WAS 2.6...37 KT. NIALA WAS

RECENTLY REDUCED TO 45 KT AND IT DOES NOT APPEAR TO BE SIGNIFICANTLY

WEAKER THAN LAST TIME...SO IN THE ABSENCE OF ANY ADDITIONAL DATA WE

WILL KEEP 45 KT AS THE INITIAL INTENSITY THIS TIME.



INITIAL MOTION IS 240/06 KT. AS AN INCREASINGLY SHALLOW

SYSTEM...NIALA IS NOW PRIMARILY STEERED BY STRONG HIGH PRESSURE FAR

NORTH OF THE MAIN HAWAIIAN ISLANDS. TRACK GUIDANCE SHOWS THAT THIS

WILL CONTINUE...WITH A TIGHTLY PACKED ENVELOPE INDICATING MOTION

TOWARD THE WEST SOUTHWEST THROUGH THE NEXT FIVE DAYS. THE CURRENT

FORECAST TRACK WAS ADJUSTED SLIGHTLY TO THE LEFT FROM THE LAST ONE

TO ACCOUNT FOR INITIAL MOTION AND ALIGN MORE CLOSELY WITH TVCN

CONSENSUS.



SHEAR ACROSS NIALA IS ANALYZED AT 30 KT FROM SHIPS AND 40 KT FROM

UW-CIMSS THIS MORNING...SO IT IS NOT SURPRISING THAT THE OVERALL

SATELLITE PRESENTATION IS OF A WEAKENING SYSTEM WITH INCREASINGLY

SPORADIC DEEP CONVECTION. INTENSITY GUIDANCE VARIES ON THE FATE OF

NIALA...WITH ECMWF AND ICON DISSIPATING THIS SYSTEM AFTER 48

AND 96 HOURS...RESPECTIVELY. GFS MAINTAINS NIALA AS A WEAK TROPICAL

LOW THROUGH 120 HOURS. MOST MODELS SHOW NIALA WEAKENING TO MINIMAL

TROPICAL STORM STRENGTH IN 24 HOURS. OUR FORECAST FOR GRADUAL

WEAKENING MATCHES THE LAST FORECAST AND FOLLOWS A BLEND OF THESE

TRENDS...WITH NIALA FORECAST TO WEAKEN BELOW TROPICAL STORM STRENGTH

AFTER 24 HOURS...THEN TO POST-TROPICAL/REMNANT LOW STATUS ON DAY

THREE. LIKE BEFORE...WE WILL NOT COMPLETELY DISSIPATE THIS SYSTEM.

VERY LONG RANGE GLOBAL MODELS DEPICT UNSPECIFIED TROPICAL

DEVELOPMENT IN THE GENERAL AREA WHERE ANY REMNANTS OF NIALA WOULD

RESIDE...SAY SEVEN TO TEN DAYS OUT.



THE TIGHT PRESSURE GRADIENT BETWEEN NIALA AND THE HIGH NORTH OF THE

HAWAIIAN ISLANDS WILL MAINTAIN STRONG TRADE WINDS...WITH LOCAL AREAS

OF GALE FORCE WINDS IN SOME CHANNELS AND COASTAL WATERS...ACROSS THE

MAIN HAWAIIAN ISLANDS AT LEAST THROUGH TONIGHT. ALSO...ABUNDANT

TROPICAL MOISTURE STREAMING UP TOWARD THE BIG ISLAND WILL CONTINUE

TO PRODUCE THE THREAT OF FLASH FLOODING ON PARTS OF THAT ISLAND

THROUGH MONDAY.





FORECAST POSITIONS AND MAX WINDS



INIT  27/2100Z 16.0N 154.5W   45 KT  50 MPH

 12H  28/0600Z 15.7N 155.4W   40 KT  45 MPH

 24H  28/1800Z 15.4N 156.5W   35 KT  40 MPH

 36H  29/0600Z 15.2N 157.7W   30 KT  35 MPH

 48H  29/1800Z 15.0N 158.9W   30 KT  35 MPH

 72H  30/1800Z 14.6N 161.0W   30 KT  35 MPH...POST-TROP/REMNT LOW

 96H  01/1800Z 13.9N 163.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

120H  02/1800Z 13.3N 164.8W   25 KT  30 MPH...POST-TROP/REMNT LOW



$$

FORECASTER POWELL