WTPZ45 KNHC 270243 RRA

TCDEP5



TROPICAL STORM MIRIAM DISCUSSION NUMBER   4

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP152018

800 PM PDT SUN AUG 26 2018



THE OVERALL CLOUD PATTERN OF MIRIAM HAS CONTINUED TO GRADUALLY

IMPROVE THIS EVENING.  HOWEVER, LIGHT NORTHERLY SHEAR OF ABOUT 10

KT, AS ANALYZED BY UW-CIMSS, SEEMS TO BE PREVENTING THE CYCLONE FROM

STRENGTHENING AT A MORE RAPID PACE.  EARLIER ASCAT DATA AND A MORE

RECENT PARTIAL AMSR OVERPASS INDICATED THAT THE LOW-LEVEL CENTER OF

MIRIAM IS SLIGHTLY DISPLACED TO THE NORTHWEST OF MOST OF THE DEEP

CONVECTION, BUT IS STILL WELL-EMBEDDED WITHIN THE CIRRUS CANOPY.  A

CONSENSUS OF OBJECTIVE AND SUBJECTIVE SATELLITE INTENSITY ESTIMATES

SUGGESTS THAT MIRIAM HAS STRENGTHENED A LITTLE SINCE THE LAST

ADVISORY, SO THE INITIAL INTENSITY HAS BEEN INCREASED TO 45 KT.



THE TROPICAL STORM IS STILL MOVING WESTWARD AT AROUND 12 KT, AND ALL

INDICATIONS ARE THAT THIS MOTION WILL CONTINUE FOR THE NEXT FEW

DAYS.  BY DAY 4, MIRIAM SHOULD TURN NORTHWARD AS IT REACHES A BREAK

IN THE SUBTROPICAL RIDGE CREATED BY AN EXTENSIVE MID- TO UPPER-LEVEL

LOW LOCATED OVER THE CENTRAL NORTH PACIFIC.  THE TRACK GUIDANCE IS

IN GOOD AGREEMENT ON THIS GENERAL SCENARIO, BUT STILL DIFFERS ON THE

EXACT TIMING AND LOCATION OF THE NORTHWARD TURN.  THE NHC FORECAST

THEREFORE REMAINS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE, AND IS

ESSENTIALLY A BLEND OF THE HCCA AND TVCX CONSENSUS AIDS AND THE

PREVIOUS FORECAST.



STEADY STRENGTHENING IS STILL LIKELY FOR THE NEXT DAY OR TWO. WHILE

MIRIAM'S STRUCTURE DOES NOT APPEAR TO BE CONDUCIVE FOR RAPID

INTENSIFICATION AT THE MOMENT, THIS COULD CHANGE QUICKLY AND WITH