WTPZ45 KNHC 291449 RRA

TCDEP5



HURRICANE ROSA DISCUSSION NUMBER  18

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP202018

800 AM PDT SAT SEP 29 2018



ROSA HAS BECOME SIGNIFICANTLY BETTER ORGANIZED DURING THE LAST

SEVERAL HOURS, LIKELY DUE TO THE COMPLETION OF AN EYEWALL

REPLACEMENT CYCLE BEFORE THE CENTER MOVED OVER COLD WATER.  THE

STORM NOW HAS A 30-40 N MI WIDE EYE, AND THE EYEWALL CONVECTIVE TOPS

HAVE BECOME MUCH COLDER AND MORE SYMMETRIC.  THE INITIAL INTENSITY

HAS BEEN INCREASED TO 90 KT BASED ON A BLEND OF VARIOUS SATELLITE

INTENSITY ESTIMATES, AND IT IS POSSIBLE THAT THIS INTENSITY IS

CONSERVATIVE.  THE HURRICANE HAS GOOD TO EXCELLENT CIRRUS OUTFLOW IN

THE NORTHEASTERN SEMICIRCLE.



THE CURRENT RE-INTENSIFICATION WAS POORLY ANTICIPATED, AND IT IS

UNCLEAR HOW MUCH MORE STRENGTHENING WILL OCCUR BEFORE ROSA REACHES

THE 26C ISOTHERM IN ABOUT 12 H.  EVEN IF THE HURRICANE STRENGTHENS

A LITTLE MORE, THE COMBINATION OF DECREASING SEA SURFACE

TEMPERATURES AND INCREASING SHEAR SHOULD CAUSE STEADY TO RAPID

WEAKENING AFTER 12 H, AND THE NEW INTENSITY FORECAST STILL CALLS FOR

THE CYCLONE TO WEAKEN BELOW HURRICANE STRENGTH BEFORE THE CENTER

REACHES THE BAJA CALIFORNIA PENINSULA BETWEEN 48-72 H.  AFTER

LANDFALL, ROSA IS EXPECTED TO WEAKEN EVEN FASTER, AND THE SURFACE

CIRCULATION IS FORECAST TO DISSIPATE JUST AFTER 72 H IN AGREEMENT

WITH ALL OF THE DYNAMICAL MODELS.  HOWEVER, THE MID-LEVEL

CIRCULATION AND THE ASSOCIATED RAINFALL WILL CONTINUE MOVING ACROSS

THE SOUTHWESTERN UNITED STATES AFTER THE SURFACE CIRCULATION

DISSIPATES.



THE INITIAL MOTION IS NOW 355/10.  DURING THE FORECAST PERIOD, THE

HURRICANE WILL RECURVE INTO THE WESTERLIES BETWEEN A DEEP-LAYER