WTPZ45 KNHC 300840 RRA

TCDEP5



HURRICANE ROSA DISCUSSION NUMBER  21

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP202018

200 AM PDT SUN SEP 30 2018



INFRARED AND MICROWAVE SATELLITE IMAGES INDICATE A CONTINUED EROSION

OF ROSA'S INNER-CORE STRUCTURE SINCE THE PREVIOUS ADVISORY DUE TO

SOUTHWESTERLY VERTICAL WIND SHEAR NEAR 20 KT ALONG WITH COLDER WATER

BENEATH THE HURRICANE AND ENTRAINMENT OF DRIER MID-LEVEL AIR IN THE

SOUTHWESTERN QUADRANT. THE INTENSITY WAS ASSESSED AS 80 KT AT 0600

UTC BASED ON THE HIGH-END ESTIMATES FROM TAFB AND UW-CIMSS ADT AND

SATCON, BUT SINCE THEN THE RAPID EROSION OF THE EYE FEATURE AND

STRONG NORTHEASTWARD TILT TO THE VORTEX COLUMN NOTED IN MICROWAVE

IMAGERY SUGGESTS A LOWER ESTIMATE OF 75 KT FOR THE ADVISORY

INTENSITY.



THIS INITIAL MOTION ESTIMATE IS 005/10 KT. ROSA IS FORECAST TO

CONTINUE MOVING NORTHWARD AROUND THE WESTERN EDGE OF A DEEP-LAYER

RIDGE FOR THE NEXT 24 H OR SO, FOLLOWED BY A TURN TOWARD THE

NORTH-NORTHEAST ON TUESDAY AS A MID-/UPPER-LEVEL TROUGH APPROACHES

FROM THE WEST. AS THE LOW- AND UPPER-LEVEL CIRCULATIONS CONTINUE

TO DECOUPLE, ROSA SHOULD ESSENTIALLY MAINTAIN ITS CURRENT FORWARD

SPEED UNTIL LANDFALL OCCURS IN 36-48 HOURS DUE TO THE CYCLONE NOT

BEING INFLUENCED BY THE FASTER DEEP-LAYER STEERING FLOW. THE NEW NHC

TRACK FORECAST IS A LITTLE SLOWER THAN THE PREVIOUS ADVISORY TRACK,

AND CLOSELY FOLLOWS THE CONSENSUS MODELS HCCA AND IVCN. A 72-HOUR

FORECAST POSITION CONTINUES TO BE PROVIDED FOR CONTINUITY PURPOSES,

BUT ROSA'S SURFACE CIRCULATION IS LIKELY TO DISSIPATE BEFORE THAT

TIME OVER NORTHWESTERN MEXICO OR SOUTHERN ARIZONA, WITH THE

MID-LEVEL REMNANTS CONTINUING NORTHWARD ACROSS THE DESERT SOUTHWEST