559
WTPA41 PHFO 281443
TCDCP1
TROPICAL DEPRESSION NIALA DISCUSSION NUMBER 15
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI CP062015
500 AM HST MON SEP 28 2015
THE LAST BURST OF DEEP CONVECTION THAT DEVELOPED JUST TO THE
EAST OF THE LOW LEVEL CIRCULATION CENTER /LLCC/ OF NIALA SUNDAY
EVENING HAS MOSTLY DISSIPATED. THERE ARE A FEW THUNDERSTORMS
REMAINING JUST TO THE EAST OF THE EXPOSED LLCC. MORE IMPORTANTLY...
INFRARED SATELLITE IMAGERY SHOWS A PATCH OF MID-LEVEL CLOUDS MOVING
ACROSS THE LLCC DURING THE PAST FEW HOURS. THIS WOULD SUGGEST THAT
NIALA IS JUST A SHALLOW SYSTEM AT THIS POINT...WITH NO ORGANIZED MID
OR UPPER LEVEL STRUCTURE REMAINING. THE MOST RECENT SUBJECTIVE
DVORAK SATELLITE INTENSITY ESTIMATES WERE 2.0/30 KT FROM JTWC...
WHILE THE PHFO AND SAB ESTIMATES WERE 1.5/25 KT. THE MOST RECENT
UW-CIMSS ADT ESTIMATE WAS 1.6/26 KT. AS A RESULT...WE HAVE WEAKENED
NIALA TO A 30 KT TROPICAL DEPRESSION.
THE INITIAL MOTION HAS SLOWED SLIGHTLY...AND IT IS NOW 250/07 KT.
THE MAIN STEERING MECHANISM FOR THE SHALLOW LLCC IS THE CIRCULATION
AROUND A BROAD SUBTROPICAL HIGH CENTERED MORE THAN 1700 NM TO THE
NORTH-NORTHEAST. HIGH PRESSURE TO THE NORTH OF NIALA WILL LIKELY
REMAIN THE PRIMARY DRIVER OF THE FUTURE TRACK DURING THE NEXT FEW
DAYS...UNTIL WHATEVER IS LEFT OF NIALA MOVES INTO AN AREA OF WEAK
STEERING DURING DAYS 4 AND 5. THE LATEST TRACK FORECAST IS SLIGHTLY
SLOWER...AND HAS BEEN NUDGED TO THE LEFT OF THE PREVIOUS
ADVISORY. THIS CLOSELY FOLLOWS THE LATEST GUIDANCE FROM THE TVCN
CONSENSUS OUTPUT...AS WELL AS THE INDIVIDUAL GFS AND HWRF MODELS.
THE LATEST ESTIMATES OF ENVIRONMENTAL VERTICAL WIND SHEAR IN THE
VICINITY OF NIALA INDICATE IT IS FROM THE WEST-SOUTHWEST AT 28 KT
BASED ON SHIPS AND 33 KT BASED ON UW-CIMSS. THIS STRONG SHEAR IS
FORECAST TO CONTINUE DURING THE NEXT FEW DAYS...SO IT IS VERY
UNLIKELY THAT NIALA WILL REDEVELOP PERSISTENT DEEP CONVECTION
NEAR ITS INNER CORE THROUGH DAY 3. THE CONVECTIVE FLARE UPS WE
CONTINUE TO SEE WILL LIKELY BECOME LESS FREQUENT...AND WILL REMAIN
DISPLACED TO THE EAST AND EAST-NORTHEAST OF THE LLCC. AS A RESULT...
WE NOW WEAKEN THE DEPRESSION TO A REMNANT LOW LATER TODAY OR
TONIGHT. AGAIN...AS IN PREVIOUS FORECAST CYCLES...WE DO NOT
ANTICIPATE THAT NIALA WILL DISSIPATE COMPLETELY. ONCE IT TRAVELS
FAR ENOUGH SOUTH...IT WILL ENCOUNTER NOT ONLY MUCH WARMER OCEAN
TEMPERATURES...IT MAY ALSO MOVE INTO A LESS HOSTILE SHEAR
ENVIRONMENT.
FORECAST POSITIONS AND MAX WINDS
INIT 28/1500Z 15.0N 156.8W 30 KT 35 MPH
12H 29/0000Z 14.7N 157.9W 25 KT 30 MPH
24H 29/1200Z 14.5N 159.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
36H 30/0000Z 14.3N 160.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 30/1200Z 14.1N 161.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 01/1200Z 13.5N 163.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 02/1200Z 13.0N 164.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 03/1200Z 12.0N 165.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
FORECASTER HOUSTON
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