WTPZ45 KNHC 262031 RRA

TCDEP5



TROPICAL STORM MIRIAM DISCUSSION NUMBER   3

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP152018

200 PM PDT SUN AUG 26 2018



MIRIAM CONTINUES TO GRADUALLY BECOME BETTER ORGANIZED.  THE LATEST

VISIBLE SATELLITE IMAGES SHOW A WELL-DEFINED CURVED BAND THAT WRAPS

ABOUT THREE-QUARTERS OF THE WAY AROUND THE CENTER.  DESPITE THE

IMPROVEMENT IN ORGANIZATION, VERY RECENT ASCAT PASSES SHOW MAXIMUM

WINDS OF ABOUT 35 KT.  THEREFORE, THE INITIAL WIND SPEED IS HELD AT

40 KT AS A COMPROMISE BETWEEN THE ASCAT DATA AND THE HIGHER

DVORAK-BASED ESTIMATES.



THE TROPICAL STORM IS MOVING WESTWARD AT ABOUT 12 KT.  THIS WESTWARD

MOTION SHOULD CONTINUE DURING THE NEXT FEW DAYS WHILE A DEEP-LAYER

RIDGE REMAINS ANCHORED TO THE NORTH OF THE TROPICAL CYCLONE.  AFTER

THAT TIME, THE STORM IS FORECAST TO TURN TO THE NORTHWEST AND THEN

THE NORTH AS A MID- TO UPPER-LEVEL LOW CAUSES A SIGNIFICANT BREAK IN

THE SUBTROPICAL RIDGE.  ALTHOUGH THE MODELS AGREE ON THIS SCENARIO,

THERE ARE SOME DIFFERENCES IN WHERE AND WHEN MIRIAM WILL MAKE THE

NORTHWARD TURN.  THE NHC TRACK FORECAST LIES NEAR THE MIDDLE OF THE

GUIDANCE ENVELOPE, NEAR THE CONSENSUS AIDS.



STEADY STRENGTHENING IS LIKELY DURING THE NEXT COUPLE OF DAYS DUE TO

THE FAVORABLE ENVIRONMENTAL FACTORS OF LOW WIND SHEAR, HIGH LEVELS

OF MOISTURE, AND WARM SSTS OF 27-28 DEG C.  THE LATEST INTENSITY

MODELS ALL SHOW MIRIAM BECOMING A HURRICANE, AND THE HWRF MODEL

SHOWS THE CYCLONE REACHING MAJOR HURRICANE STRENGTH.  THE NHC

INTENSITY FORECAST CONTINUES TO LEAN TOWARD THE HIGHER END OF THE

MODEL GUIDANCE, AND IT IS IN BEST AGREEMENT WITH HFIP CORRECTED

CONSENSUS APPROACH MODEL.  BY THE END OF THE FORECAST PERIOD, WHEN