WTPZ45 KNHC 290233 RRA

TCDEP5



TROPICAL STORM MIRIAM DISCUSSION NUMBER  12

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP152018

800 PM PDT TUE AUG 28 2018



THERE'S BEEN LITTLE CHANGE IN THE OVERALL CLOUD PATTERN OF MIRIAM

DURING THE PAST SEVERAL HOURS.  AN EARLIER ADVANCED TECHNOLOGY

MICROWAVE SOUNDER (ATMS) OVERPASS AND A 2053 UTC GCOM-W1 AMSR2 IMAGE

INDICATE THAT THE SURFACE CENTER IS STILL SHEARED TO THE NORTHWEST

OF THE DEEP CONVECTIVE BANDING FEATURE ENCOMPASSING THE SOUTHERN

PORTION OF THE CYCLONE.  DVORAK SATELLITE INTENSITY ESTIMATES FROM

TAFB AND SAB REMAIN UNCHANGED, AND A 2213 UTC SATCON ANALYSIS

SHOWED 51 KT.  BASED ON THESE DATA, THE INITIAL INTENSITY IS HELD

AT 50 KT.



THE INTENSITY FORECAST IS RATHER PROBLEMATIC THIS EVENING.

DECAY SHIPS GUIDANCE (BOTH GFS AND ECMWF BACKGROUND FIELDS) SHOWS

THE MODERATE NORTHWESTERLY SHEAR INCREASING AFTER 48 HOURS, WHILE

INDICATING LITTLE CHANGE IN STRENGTH UP TO THAT PERIOD.  AFTER THAT

TIME, THESE STATISTICAL/DYNAMICAL GUIDANCE MODELS QUICKLY DEGENERATE

THE CYCLONE INTO A REMNANT LOW IN 4 DAYS.  THE NOAA-HCCA, HWRF, AND

THE IVCN CONSENSUS MODEL, ON THE OTHER HAND, ALL SHOW MIRIAM

BECOMING A HURRICANE IN 36-48 HOURS.  FOR THIS ADVISORY, I'VE

ELECTED TO MAINTAIN CONTINUITY AND SHOW GRADUAL STRENGTHENING TO

JUST BELOW HURRICANE STRENGTH IN 36 HOURS, WITH A WEAKENING TREND

COMMENCING IN 3 DAYS.  ALL THE DETERMINISTIC MODELS AGREE WITH

MIRIAM BECOMING A REMNANT LOW IN 5 DAYS, AND THIS IS REFLECTED IN

THE NHC FORECAST.



THE INITIAL MOTION IS ESTIMATED TO BE WESTWARD, OR 270/11 KT,

WITHIN THE EASTERLY MID-LEVEL STEERING FLOW PRODUCED BY A

MID-TROPOSPHERIC HIGH TO THE NORTH OF MIRIAM.  THE CYCLONE IS