WTPZ45 KNHC 302033 RRA

TCDEP5



HURRICANE ROSA DISCUSSION NUMBER  23

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP202018

200 PM PDT SUN SEP 30 2018



AN AIR FORCE RESERVE UNIT HURRICANE HUNTER AIRCRAFT RECENTLY

INVESTIGATED ROSA, AND FOUND PEAK 700-MB FLIGHT-LEVEL WINDS THAT

STILL SUPPORTED MINIMAL HURRICANE INTENSITY.  HOWEVER, THE

SFMR-OBSERVED SURFACE WINDS WERE SOMEWHAT LOWER, WHICH IS NOT

SURPRISING SINCE THE SYSTEM HAS MINIMAL DEEP CONVECTION AND IS OVER

24-25 DEG SSTS.  GIVEN THAT THE CENTRAL PRESSURE IS STILL FAIRLY

LOW, 982 MB, ROSA IS BEING MAINTAINED, PERHAPS GENEROUSLY, AS A

HURRICANE FOR THIS ADVISORY.  WITH INCREASING SHEAR AND COOLER

WATERS AHEAD FOR THE SYSTEM, WEAKENING SEEMS INEVITABLE.  THE

OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE LATEST HWRF MODEL

PREDICTION, AND SHOWS ROSA WEAKENING TO A DEPRESSION BY THE TIME IT

REACHES THE SOUTHWEST UNITED STATES.



THE INITIAL MOTION IS NORTH-NORTHEASTWARD, OR 025/10 KT.  THE TRACK

FORECAST SCENARIO REMAINS ESSENTIALLY UNCHANGED FROM THE PREVIOUS

COUPLE OF ADVISORY PACKAGES.  THE FLOW ON THE EASTERN SIDE OF A

LARGE MID-LEVEL TROUGH APPROACHING FROM THE WEST SHOULD STEER ROSA

ON A NORTH-NORTHEASTWARD TRACK FOR THE NEXT COUPLE OF DAYS.  THE

OFFICIAL TRACK FORECAST IS VERY CLOSE TO THE LATEST DYNAMICAL MODEL

CONSENSUS.



THE WIND RADII HAVE BEEN ADJUSTED SLIGHTLY BASED ON DATA FROM A

RECENT ASCAT SCATTEROMETER OVERPASS.



KEY MESSAGES:



1. THE MAIN HAZARD EXPECTED FROM ROSA OR ITS REMNANTS IS VERY HEAVY

RAINFALL IN BAJA CALIFORNIA, NORTHWESTERN SONORA, AND THE U.S.

DESERT SOUTHWEST.  THESE RAINS ARE EXPECTED TO PRODUCE

LIFE-THREATENING FLASH FLOODING AND DEBRIS FLOWS IN THE DESERTS, AND