WTPZ45 KNHC 270835 RRA

TCDEP5



TROPICAL STORM MIRIAM DISCUSSION NUMBER   5

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP152018

200 AM PDT MON AUG 27 2018



MIRIAM'S CLOUD PATTERN AND OVERALL CONVECTIVE ORGANIZATION HAVE

CONTINUED TO IMPROVE, WITH A TIGHT COMMA-CLOUD PATTERN NOW EVIDENT

IN INFRARED IMAGERY.  TWO RECENT ASCAT PASSES AROUND 0600Z INDICATE

THAT THE LOW-LEVEL CENTER IS NOW LOCATED JUST INSIDE THE NORTHWEST

QUADRANT OF THE CONVECTIVE COMMA HEAD, AND THAT THE RADIUS OF

MAXIMUM WINDS (RMW) IS STILL ABOUT 20 NMI THAT WAS ASCERTAINED FROM

EARLIER PASSIVE MICROWAVE LOW-LEVEL RING DATA. THE ASCAT DATA

INDICATED PEAK WINDS OF ONLY 37 KT, BUT THIS IS LIKELY AN

UNDERESTIMATE OF MIRIAM'S ACTUAL INTENSITY DUE TO A) THE DATA HAVING

BEEN LOCATED NEAR THE SWATH EDGE AND B) DUE TO MIRIAM'S SMALL RMW.

THE ADVISORY INTENSITY OF 50 KT IS BASED ON A AVERAGE OF SUBJECTIVE

AND OBJECTIVE SATELLITE INTENSITY ESTIMATES THAT RANGE FROM T3.0/45

KT TO T3.6/57 KT, RESPECTIVELY. THE PREVIOUS ADVISORY'S 34-KT WIND

RADII REMAIN UNCHANGED BASED ON THE AFOREMENTIONED ASCAT WIND DATA.



MIRIAM IS NOW MOVING DUE WEST OR 270/13 KT. THERE ARE NO SIGNIFICANT

CHANGES TO THE PREVIOUS FORECAST TRACK OR REASONING. THE CYCLONE IS

EXPECTED TO MAINTAIN A GENERAL WESTWARD MOTION FOR THE NEXT 72 H AS

MIRIAM MOVES ALONG THE SOUTHERN PERIPHERY OF A STRONG RIDGE TO ITS

NORTH. BY 96 H AND BEYOND, MIRIAM IS FORECAST TO MOVE NORTHWARD TO

NORTH-NORTHWESTWARD THROUGH A BREAK IN THE SUBTROPICAL RIDGE NEAR

CREATED BY A STRONG MID- TO UPPER-LEVEL TROUGH/LOW FORECAST TO DROP

SOUTHWARD BETWEEN 140W-150W FROM THE UPPER-LOW'S CURRENT POSITION

OVER THE CENTRAL NORTH PACIFIC. THE LATEST MODEL GUIDANCE HAS COME