WTPZ41 KNHC 010237 RRA

TCDEP1



TROPICAL STORM SERGIO DISCUSSION NUMBER   7

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212018

900 PM MDT SUN SEP 30 2018



OVERALL, SERGIO HAS CHANGED LITTLE IN ORGANIZATION OVER THE PAST

SEVERAL HOURS.  THE CONVECTIVE PATTERN IS COMPRISED OF A RAGGED

BAND WRAPPING ABOUT THREE-QUARTERS OF THE WAY AROUND THE CENTER,

WITH THE STRONGEST CONVECTION TO THE NORTH OF THE CENTER.  RECENT

MICROWAVE DATA SHOW THAT THE MID-LEVEL CIRCULATION CENTER SEEN

EARLIER HAS LOST SOME DEFINITION.  HOWEVER, THE LOW-LEVEL

CIRCULATION CENTER SEEMS TO BE BECOMING BETTER DEFINED.  THE

INITIAL INTENSITY REMAINS 55 KT BASED ON UNCHANGED SATELLITE

INTENSITY ESTIMATES.



THE INITIAL MOTION REMAINS 260/11.  FOR THE NEXT 36 H OR SO, SERGIO

SHOULD MOVE WESTWARD OR JUST SOUTH OF DUE WESTWARD AROUND THE

SOUTHERN PERIPHERY OF A LARGE DEEP-LAYER SUBTROPICAL RIDGE EXTENDING

FROM MEXICO WESTWARD ACROSS THE EASTERN PACIFIC.  AFTER THAT TIME, 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

DEVELOPMENT WILL ALLOW SERGIO TURN WEST-NORTHWESTWARD TO

NORTHWESTWARD WITH A GRADUAL DECREASE IN FORWARD SPEED.  THE NEW

FORECAST TRACK IS NEAR THE VARIOUS CONSENSUS MODELS AND IS AN

UPDATE OF THE PREVIOUS TRACK.



CONDITIONS APPEAR FAVORABLE FOR SERGIO TO RAPIDLY INTENSIFY IN THE

NEXT 36 H IF THE CYCLONE CAN BECOME WELL ENOUGH ORGANIZED TO TAKE

ADVANTAGE OF THE ENVIRONMENT.  THIS PART OF THE INTENSITY FORECAST

PRESUMES THIS WILL HAPPEN AND IS UNCHANGED FROM THE PREVIOUS

FORECAST OF QUICK STRENGTHENING.  FROM 36-48 H, A BURST OF

NORTHEASTERLY SHEAR IS EXPECTED TO AFFECT SERGIO, WHICH SHOULD AT