WTPZ41 KNHC 300854 RRA

TCDEP1



TROPICAL STORM SERGIO DISCUSSION NUMBER   4

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP212018

400 AM CDT SUN SEP 30 2018



MICROWAVE AND INFRARED SATELLITE IMAGES, ALONG WITH SCATTEROMETER

WIND DATA, INDICATE THAT SERGIO HAS CONTINUED TO BECOME BETTER

ORGANIZED, WITH STRONG CONVECTION NOW MORE CONCENTRATED NEAR THE

CENTER. HOWEVER, SCATTEROMETER DATA SHOWED THAT THE INNER-CORE WIND

FIELD IS STILL RATHER LOOSE AND NOT PARTICULARLY WELL-DEFINED QUITE

YET. THE INITIAL INTENSITY HAS BEEN INCREASED TO 45 KT BASED ON A

DVORAK SATELLITE INTENSITY ESTIMATE OF T3.0/45 KT FROM TAFB AND

SAB, WHICH IS SUPPORTED BY A 0536 UTC ASCAT PASS THAT CONTAINED A

FEW 45-KT VECTORS EAST OF THE CENTER.



THE INITIAL MOTION ESTIMATE IS 270/10 KT. THERE IS NO SIGNIFICANT

CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. FOR THE NEXT 48

HOURS OR SO, SERGIO SHOULD MOVE GENERALLY WESTWARD ALONG THE

SOUTHERN PERIPHERY OF A LARGE, DEEP-LAYER SUBTROPICAL RIDGE THAT

EXTENDS FROM MEXICO WESTWARD ACROSS THE EASTERN AND CENTRAL PACIFIC.

BY 72 HOURS, A BROAD MID- TO UPPER-LEVEL TROUGH IS FORECAST TO DROP

SOUTHWARD AND SOUTHEASTWARD OVER THE SOUTHWESTERN U.S. AND THE

NORTHEASTERN PACIFIC, PRODUCING A BREAK IN THE RIDGE WHICH WILL

ALLOW SERGIO TO MOVE TOWARD THE NORTHWEST AT A SLOWER FORWARD

SPEED THROUGH 120 HOURS. THE NEW NHC TRACK FORECAST IS SIMILAR TO

BUT SLIGHTLY SOUTH OF THE PREVIOUS ADVISORY TRACK, AND LIES CLOSE

TO AN AVERAGE OF THE CONSENSUS MODELS TVCE, HCCA, AND FSSE.



SERGIO IS FORECAST TO REMAIN IN A LOW-SHEAR, WARM-WATER, AND

HIGH-MOISTURE ENVIRONMENT FOR THE NEXT 36 HOURS OR SO, DURING WHICH