WTPA41 PHFO 280254

TCDCP1



TROPICAL STORM NIALA DISCUSSION NUMBER  13

NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   CP062015

500 PM HST SUN SEP 27 2015



NIALA IS NOW DEVOID OF DEEP CONVECTION...AND HAS BEEN SINCE ABOUT

2200 UTC. THE WELL-DEFINED LOW CLOUD SWIRL KEEPS FIX CONFIDENCE HIGH

THIS AFTERNOON. SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES

REFLECT THIS WORSENING SATELLITE PRESENTATION...WITH 2.5...35

KT...GIVEN BY ALL THREE SATELLITE CENTERS. UW-CIMSS ADT WAS 2.7...39

KT. HOWEVER...A 1935 UTC ASCAT PASS SHOWED A 50 NM WIDE SWATH OF 40

KT WINDS ACROSS THE NORTHERN SEMICIRCLE. SOME TIME HAS PASSED SINCE

THEN...BUT WE WILL DROP THE INITIAL INTENSITY TO A POSSIBLY GENEROUS

40 KT...INSTEAD OF 35 KT...IN A NOD TO THAT ASCAT PASS.



INITIAL MOTION IS 250/08 KT...REPRESENTING A NOTICEABLE INCREASE IN

FORWARD SPEED SINCE THIS MORNING. A WEAKENING NIALA CONTINUES TO BE

STEERED BY STRONG HIGH PRESSURE FAR NORTH OF THE MAIN HAWAIIAN

ISLANDS...SO IT SHOULD BE EXPECTED THAT SYSTEM MOTION WOULD SLOWLY

APPROACH BACKGROUND LOW LEVEL ENVIRONMENTAL FLOW. TRACK GUIDANCE

SHOWS THIS...REMAINING TIGHTLY CLUSTERED AND TAKING NIALA TOWARDS

THE WEST SOUTHWEST TO SOUTHWEST THROUGH FIVE DAYS. THE CURRENT

FORECAST TRACK CLOSELY FOLLOWS THE LAST ONE...WITH FASTER MOVEMENT

THROUGH 36 HOURS FOLLOWED BY SLOWER MOTION AFTERWARDS AS PER

CONSENSUS MODELS.



SHEAR ACROSS NIALA IS ANALYZED AT 32 KT FROM SHIPS AND 43 KT FROM

UW-CIMSS THIS AFTERNOON...SO IT IS NOT SURPRISING THAT NIALA IS

WEAKENING EVEN AS IT PASSES OVER INCREASINGLY WARM WATER. INTENSITY

GUIDANCE UNANIMOUSLY WEAKENS NIALA...BUT AT VARIOUS RATES. ECMWF

AND ICON COMPLETELY DISSIPATE THIS SYSTEM AFTER 48 AND 72

HOURS...RESPECTIVELY...WHILE MODELS LIKE GFS AND HWRF KEEP NIALA

ALIVE AS A REMNANT LOW THROUGH 120 HOURS. OUR FORECAST WEAKENS

NIALA TO A DEPRESSION AT 24 HOURS...THEN TO A POST-TROPICAL/REMNANT

LOW AT 48 HOURS. HOWEVER...LIKE THE LAST FEW FORECAST CYCLES...WE DO

NOT DISSIPATE THIS SYSTEM COMPLETELY. LONG RANGE GLOBAL MODELS

DEPICT UNSPECIFIED TROPICAL DEVELOPMENT IN THE GENERAL AREA

SOUTHWEST OF THE HAWAIIAN ISLANDS WHERE ANY REMNANTS OF NIALA WOULD

LINGER IN SEVEN TO TEN DAYS.



THERE ARE NO WATCHES...WARNINGS OR ADVISORIES ASSOCIATED WITH

NIALA...BUT THERE CONTINUE TO BE REAL HAZARDS ACROSS PORTIONS OF

THE MAIN HAWAIIAN ISLANDS RELATED TO MOISTURE AND SWELL BROUGHT

IN BY STRONG TRADE WINDS...ALONG WITH THE DIMINISHING RESIDUAL NIALA

SWELL MAINLY TO THE BIG ISLAND. THESE WINDS ARE DRIVEN BY THE HIGH

FAR NORTH OF THE MAIN HAWAIIAN ISLANDS...THE SAME HIGH PUSHING NIALA

ALONG. THE HONOLULU WFO CONTINUES TO ISSUE FLOOD WATCH AND HIGH SURF

ADVISORY PRODUCTS...ALONG WITH PRODUCTS DESCRIBING MARINE AND

AVIATION HAZARDS...RELATED TO THIS STRONG TRADE WIND FLOW.





FORECAST POSITIONS AND MAX WINDS



INIT  28/0300Z 15.7N 155.5W   40 KT  45 MPH

 12H  28/1200Z 15.4N 156.7W   35 KT  40 MPH

 24H  29/0000Z 15.1N 158.3W   30 KT  35 MPH

 36H  29/1200Z 14.8N 159.7W   30 KT  35 MPH

 48H  30/0000Z 14.4N 161.1W   25 KT  30 MPH...POST-TROP/REMNT LOW

 72H  01/0000Z 13.7N 163.3W   25 KT  30 MPH...POST-TROP/REMNT LOW

 96H  02/0000Z 13.1N 165.2W   25 KT  30 MPH...POST-TROP/REMNT LOW

120H  03/0000Z 12.6N 166.7W   25 KT  30 MPH...POST-TROP/REMNT LOW



$$

FORECASTER POWELL