WTPZ42 KNHC 012055 RRA

TCDEP2



TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER   4

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172018

300 PM MDT SAT SEP 01 2018



ASCAT SCATTEROMETER OVERPASSES AT 1625Z AND 1704Z INDICATED THAT

THE DEPRESSION'S INNER-CORE WIND FIELD REMAINS ELONGATED

NORTHEAST-TO-SOUTHWEST, WITH A SECOND FULLY EXPOSED LOW-LEVEL SWIRL

LOCATED NEAR THE NORTHEASTERN END OF THE WIND FIELD. THERE WAS ALSO

A FAIRLY LARGE FIELD OF 27-29 KT SURFACE WIND VECTORS LOCATED IN THE

SOUTHERN QUADRANT. VARIOUS DVORAK SATELLITE INTENSITY ESTIMATES HAVE

REMAINED UNCHANGED SINCE THE PREVIOUS ADVISORY, SO THE INITIAL

INTENSITY IS BEING HELD AT 30 KT FOR THIS ADVISORY.



THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 285/10 KT. MOST OF THE

GLOBAL AND REGIONAL MODELS TAKE THE CYCLONE WEST-NORTHWESTWARD FOR

THE NEXT 24 H OR SO, AND THEN MOVE IT WESTWARD THEREAFTER. THE

EXCEPTION IS THE NEW GFS MODEL RUN, WHICH TAKES THE SYSTEM NORTHWARD

FOR 36 H BEFORE TURNING IT BACK WESTWARD. THE GFS APPEARS TO HAVE

KEYED IN ON THE AFOREMENTIONED EXPOSED LOW-LEVEL SWIRL NOTED IN THE

ASCAT AND RECENT VISIBLE SATELLITE DATA, AND MAKES IT THE PRIMARY

CIRCULATION CENTER. THE OFFICIAL FORECAST TRACK CALLS FOR THE MAIN

LOW-LEVEL CENTER TO REMAIN/DEVELOP CLOSER TO THE STRONGER DEEP

CONVECTION AND STRONGEST LOW-LEVEL WINDS AND ASSOCIATED VORTICITY.

THE MORE NORTHERN TRACK OF THE GFS MODEL IS BEING DISCOUNTED, BUT IT

HAS STRONGLY SKEWED THE VARIOUS CONSENSUS TRACKS FARTHER TO THE

NORTH.  AS A RESULT, THE NEW OFFICIAL FORECAST TRACK LIES SOUTH OF

THE CONSENSUS MODEL HCCA, AND IS CLOSE TO THE PREVIOUS ADVISORY

TRACK AND A BLEND OF THE MORE WESTERLY HWRF AND ECMWF MODELS.