WTNT45 KNHC 141450 RRA

TCDAT5



TROPICAL STORM IAN DISCUSSION NUMBER   9

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102016

1100 AM AST WED SEP 14 2016



IAN'S CENTER HAS LOST SOME DEFINITION AND APPEARS TO HAVE RE-FORMED

NORTH OF THE FEATURE WE HAD BEEN TRACKING.  THE CENTER REMAINS

EXPOSED TO THE SOUTH AND SOUTHEAST OF THE DEEP CONVECTION DUE TO

ALMOST 30 KT OF VERTICAL SHEAR.  BASED ON THE DVORAK CURRENT

INTENSITY NUMBER FROM TAFB, THE ESTIMATED MAXIMUM WINDS REMAIN 45

KT.



DUE TO THE CENTER'S RE-FORMATION, THE INITIAL MOTION IS A FASTER

355/17 KT.  HOWEVER, UNLESS THE CENTER JUMPS AGAIN, THIS MOTION IS

EXPECTED TO STABILIZE BACK TO AROUND 14 KT IN THE NEXT 12 HOURS.  A

MID-/UPPER-LEVEL LOW TO THE WEST OF IAN AND A MID-TROPOSPHERIC HIGH

TO THE EAST SHOULD STEER THE CYCLONE NORTHWARD AND NORTH-

NORTHEASTWARD DURING THE NEXT DAY OR SO.  AFTER THAT TIME, IAN IS

EXPECTED TO ACCELERATE TOWARD THE NORTHEAST AS IT GETS PICKED UP BY

A PROGRESSIVE MID-LATITUDE TROUGH MOVING EASTWARD FROM ATLANTIC

CANADA.  THE NEW TRACK GUIDANCE AGREES ON THIS SCENARIO, ALTHOUGH A

SLIGHT WESTWARD SHIFT IN THE OFFICIAL TRACK FORECAST WAS REQUIRED,

PROBABLY DUE TO THE UPDATED INITIAL POSITION.  THE NEW NHC FORECAST

IS VERY CLOSE TO THE TVCN MULTI-MODEL CONSENSUS.



ALTHOUGH THE VERTICAL SHEAR IS EXPECTED TO DECREASE ONLY SLIGHTLY,

MARGINALLY WARM WATERS AND IAN'S BAROCLINIC INTERACTION WITH THE

MID-/UPPER-LEVEL LOW TO ITS WEST ARE EXPECTED TO FOSTER SOME

STRENGTHENING DURING THE NEXT 36 HOURS.  IAN IS THEN EXPECTED TO

LOSE THE LAST OF ITS TROPICAL CHARACTERISTICS AND BECOME

EXTRATROPICAL BY 48 HOURS AND THEN BE ABSORBED BY ANOTHER=