WTPZ41 KNHC 302035 RRA

TCDEP1



TROPICAL STORM SERGIO DISCUSSION NUMBER   6

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212018

300 PM MDT SUN SEP 30 2018



SATELLITE IMAGERY OVER THE PAST SEVERAL HOURS AS WELL AS MICROWAVE

AND SCATTEROMETER DATA INDICATE THAT THE CENTER OF SERGIO IS

FARTHER SOUTH THAN PREVIOUSLY ANALYZED. THE DEEP CONVECTION NEAR

THE CENTER HAS BECOME RAGGED IN APPEARANCE AND ELONGATED FROM

EAST-WEST.  HOWEVER, MICROWAVE DATA CONTINUES TO SHOW A WELL-DEFINED

MID-LEVEL CIRCULATION, AND SATELLITE INTENSITY ESTIMATES ARE

UNANIMOUSLY SUPPORTING 55 KT, WHICH WILL BE THE INITIAL INTENSITY

FOR THIS ADVISORY.



THE INITIAL MOTION ESTIMATE IS NOW 260/11 KT, PARTIALLY DUE TO

ADJUSTMENT OF THE CENTER FARTHER SOUTH. OTHERWISE, THERE ARE NO

CHANGES IN THE FORECAST TRACK PHILOSOPHY FROM THE PREVIOUS ADVISORY.

FOR THE NEXT COUPLE OF DAYS, SERGIO SHOULD MOVE GENERALLY WESTWARD

OR JUST SOUTH OF DUE WEST AROUND THE SOUTHERN PERIPHERY OF A LARGE

DEEP-LAYER SUBTROPICAL RIDGE EXTENDING FROM MEXICO WESTWARD

ACROSS THE EASTERN PACIFIC. BY 48 HOURS, A MID- TO UPPER-LEVEL

TROUGH MOVING SOUTHEASTWARD ALONG AND OFFSHORE OF THE WESTERN U.S.

WILL ERODE THE WESTERN PART OF THE RIDGE. THIS WILL ALLOW THE

CYCLONE TO TURN WEST-NORTHWESTWARD TO NORTHWESTWARD FROM 48- TO

96-HOURS WITH A GRADUAL DECREASE IN FORWARD SPEED. VERY NEAR THE END

OF THE FORECAST PERIOD, THE TROUGH SHOULD SHIFT EASTWARD AND LOW-

TO MID-LEVEL RIDGING SHOULD BUILD TO THE NORTHWEST OF THE CYCLONE.

THIS PATTERN CHANGE SHOULD INDUCE A MORE WESTWARD TURN BY 120 HOURS.



DESPITE THE CURRENT RAGGED APPEARANCE OF THE CYCLONE, THE

ENVIRONMENT OF LOW-SHEAR, HIGH-MOISTURE, AND WARM WATERS ARE