077
WTPA41 PHFO 270249
TCDCP1
TROPICAL STORM NIALA DISCUSSION NUMBER 9
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP062015
500 PM HST SAT SEP 26 2015
SINCE THE LOW LEVEL CIRCULATION CENTER...LLCC...BECAME EXPOSED THIS
MORNING...THE MYSTERY CONCERNING THE LOCATION OF NIALA HAS BEEN
REMOVED. A SECOND BURST OF DEEP CONVECTION JUST NORTHEAST OF THE
LLCC HAS BEGUN TO SUBSIDE...LEAVING A WELL-DEFINED LOW CLOUD SWIRL.
OVERALL PRESENTATION CONTINUES TO BE OF A SYSTEM UNDERGOING
DEBILITATING WEST SOUTHWEST SHEAR...WITH THE ONLY OUTFLOW CHANNEL
CONTINUING TO BE TOWARDS THE NORTHEAST. UW-CIMSS NOW ANALYZES 40 KT
OF SHEAR...WHILE SHIPS SHOWS 25 KT. NEITHER VALUE IS HEALTHY FOR A
TROPICAL CYCLONE. SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES
RANGE FROM 3.5...55 KT...FROM SAB AND PHFO...TO 3.0...45 KT...FROM
JTWC. UW-CIMSS ESTIMATES NIALA INTENSITY IS 50 KT. BETWEEN 2300 UTC
AND 0000 UTC...NIALA PASSED ABOUT 40 NM SOUTH OF BUOY FOUR...WHICH
REPORTED A PEAK WIND OF 47 KT BETWEEN THOSE HOURS. GIVEN THIS
STRENGTH AND DISTANCE FROM THE LLCC...AND IN AGREEMENT WITH TWO OF
THE THREE SATELLITE CENTERS...WE WILL KEEP NIALA AT 55 KT FOR THIS
ADVISORY.
INITIAL MOTION IS 270/07 KT. SINCE MOST ASSOCIATED DEEP CONVECTION
IS GONE...PRIMARY STEERING FOR NIALA WILL BE PROVIDED BY THE STRONG
HIGH PRESSURE CENTER FAR NORTH OF HAWAII. THIS HIGH IS ALREADY
DRIVING NEAR-GALE FORCE EAST NORTHEAST TRADE WINDS ACROSS PORTIONS
OF THE ALOHA STATE AND SURROUNDING WATERS...AND WILL LIKELY FORCE
NIALA TO ASSUME A WEST SOUTHWEST MOTION WITHIN 48 HOURS. THE
CURRENT FORECAST TRACK CLOSELY FOLLOWS THE PREVIOUS ONE...KEEPING
NIALA MOVING WESTWARD THROUGH SUNDAY...THEN CURVING ITS TRACK
GENTLY WEST SOUTHWESTWARD WITHIN PREVAILING LOW LEVEL FLOW
AFTERWARDS. FORWARD MOTION HAS BEEN INCREASED SLIGHTLY THROUGH DAY
FIVE...IN KEEPING WITH CONSENSUS TRACK GUIDANCE...MOVING UP THE
TIME OF CLOSEST APPROACH TO THE BIG ISLAND TO SUNDAY AFTERNOON
VERSUS SUNDAY EVENING. WITH NIALA NOT EXPECTED TO
REINTENSIFY...THERE IS SIMPLY NOTHING TO SLOW NIALA DOWN AS IT
WEAKENS. ALTHOUGH THE TROPICAL STORM WATCH FOR THE BIG ISLAND WILL
REMAIN IN PLACE THROUGH THIS CYCLE...THE ONSET AND CUMULATIVE
PROBABILITIES FOR TROPICAL STORM FORCE WINDS THERE HAVE
DECREASED...THANKS TO A COMBINATION OF WESTERLY SYSTEM MOTION AND A
PAIR OF INITIAL FORECAST POINTS FARTHER SOUTH THAN ANTICIPATED WHEN
THE WATCH WAS INITIALLY ISSUED. IT MAY BE POSSIBLE TO CANCEL THE
WATCH LATER TONIGHT IF CURRENT TRENDS HOLD.
INTENSITY GUIDANCE ALMOST UNANIMOUSLY WEAKENS NIALA THROUGH FIVE
DAYS...WITH ICON AND SHIPS DISSIPATING THIS SYSTEM COMPLETELY AFTER
48 HOURS. IN CONTRAST...GLOBAL MODELS KEEP NIALA ALIVE AT TROPICAL
STORM STRENGTH THROUGH THE FORECAST PERIOD. OUR FORECAST OF GRADUAL
WEAKENING IS A BLEND OF THESE TRENDS...REDUCING NIALA TO A
POST TROPICAL/REMNANT LOW ON DAY FOUR...BUT NOT DISSIPATING IT
COMPLETELY.
FORECAST POSITIONS AND MAX WINDS
INIT 27/0300Z 16.9N 152.8W 55 KT 65 MPH
12H 27/1200Z 16.9N 153.9W 50 KT 60 MPH
24H 28/0000Z 16.7N 155.3W 45 KT 50 MPH
36H 28/1200Z 16.3N 156.6W 40 KT 45 MPH
48H 29/0000Z 15.9N 158.0W 35 KT 40 MPH
72H 30/0000Z 15.1N 160.6W 30 KT 35 MPH
96H 01/0000Z 14.4N 163.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 02/0000Z 14.0N 166.2W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
FORECASTER POWELL
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