WTPZ45 KNHC 260845 RRA

TCDEP5



TROPICAL STORM ROSA DISCUSSION NUMBER   5

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP202018

300 AM MDT WED SEP 26 2018



AFTER STEADILY INTENSIFYING YESTERDAY, ROSA'S STRENGTHENING TREND

HAS TEMPORARILY PAUSED.  THE TROPICAL STORM HAS A WELL-DEFINED

CURVED BAND THAT WRAPS ABOUT THREE-QUARTERS OF THE WAY AROUND THE

CENTER.  HOWEVER, SOME DRY AIR APPEARS TO BE INTRUDING INTO THE CORE

FROM THE NORTHEASTERN QUADRANT, WHICH COULD BE THE REASON WHY ROSA

HAS STOPPED STRENGTHENING FOR NOW.  THE DVORAK CLASSIFICATIONS FROM

TAFB AND SAB REMAIN 3.5/55 KT, SO THE INITIAL INTENSITY IS HELD AT

THAT VALUE.  THIS WIND SPEED IS ALSO CLOSE TO THE LATEST SATCON

ESTIMATE FROM CIMSS AT THE UNIVERSITY OF WISCONSIN.



A STRENGTHENING TREND IS EXPECTED TO RESUME SOON, AND IT SEEMS

LIKELY THAT ROSA WILL RAPIDLY INTENSIFY DURING THE NEXT COUPLE OF

DAYS WHILE IT REMAINS OVER WARM SSTS AND IN AN ENVIRONMENT OF LOW

WIND SHEAR OF 10 KT OR LESS.  THE NHC INTENSITY FORECAST CLOSELY

FOLLOWS THE HCCA MODEL, AND BRINGS ROSA TO HURRICANE STRENGTH LATER

TODAY AND MAJOR HURRICANE STRENGTH ON THURSDAY.  BEYOND A FEW DAYS,

STEADY WEAKENING IS FORECAST DUE TO COOLER SSTS, DRY AND STABLE AIR,

AND AN INCREASE IN SOUTHWESTERLY WIND SHEAR.



THE TROPICAL STORM IS MOVING WEST-NORTHWESTWARD AT 7 KT, STEERED BY

A MID-LEVEL RIDGE TO ITS NORTH.  A WEST TO WEST-NORTHWEST MOTION AT

ABOUT THE SAME FORWARD SPEED IS EXPECTED FOR THE NEXT COUPLE OF DAYS

AS THE PATTERN HOLDS.  AFTER THAT TIME, THE RIDGE IS EXPECTED TO

BREAK DOWN AS A LARGE, DEEP-LAYER LOW MOVES TOWARD THE U.S. WEST

COAST.  THIS CHANGE IN THE STEERING FLOW SHOULD CAUSE ROSA TO MOVE