WTNT42 KNHC 182059 RRA

TCDAT2



TROPICAL STORM KARL DISCUSSION NUMBER  18

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016

500 PM AST SUN SEP 18 2016



DEEP CONVECTION HAS GRADUALLY BEEN INCREASING AND BECOMING A LITTLE

BETTER ORGANIZED SINCE THE PREVIOUS ADVISORY NOW THAT LIGHT

UPPER-LEVEL SOUTHEASTERLY FLOW HAS REPLACED THE PREVIOUS HOSTILE

VERTICAL WIND SHEAR CONDITIONS. VISIBLE SATELLITE IMAGERY AND ASCAT

SURFACE WIND DATA FROM 1200Z-1300Z INDICATE THAT KARL'S CIRCULATION

REMAINS WELL-DEFINED, ESPECIALLY THE INNER-CORE WIND FIELD. THE

ASCAT DATA ALSO REVEALED A LARGE PATCH OF 35-KT WINDS 60-100 NMI

NORTH AND NORTHEAST OF THE CENTER, AND THAT IS THE INTENSITY USED

FOR THIS ADVISORY. THE ASCAT DATA SUPPORTS TRIMMING BACK THE 34-KT

WIND RADIUS IN THE NORTHEASTERN QUADRANT.



KARL CONTINUES TO MOVE WESTWARD OR 275/13 KT. KARL IS EXPECTED TO

MOVE WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE BERMUDA-AZORES

RIDGE FOR THE NEXT COUPLE OF DAYS, FOLLOWED BY A WEST-NORTHWESTWARD

MOTION ON DAYS 3-5 AS THE CYCLONE APPROACHES A WEAKNESS IN THE RIDGE

LOCATED BETWEEN BERMUDA AND THE BAHAMAS. THE GLOBAL AND REGIONAL

MODELS ARE IN GENERAL AGREEMENT ON THIS TRACK SCENARIO THROUGH 72

HOURS, AFTER THAT TIME, THE MODELS DIVERGE SIGNIFICANTLY WITH THE

GFS, NAVY COAMPS, AND GFDL MODELS TAKING KARL FARTHER WEST AS A

WEAKER AND MORE SHALLOW CYCLONE, WHEREAS THE ECMWF, UKMET, AND HWRF

MODELS MOVE KARL MORE NORTHWESTWARD AS A STRONGER AND DEEPER SYSTEM.

FOR NOW, THE OFFICIAL FORECAST TRACK REMAINS A COMPROMISE BETWEEN

THESE EXTREMES, CLOSE TO THE CONSENSUS MODEL SOLUTIONS, DUE TO THE

LACK OF A STABLE, CONSISTENT RUN-TO-RUN FORECAST BY THE MODELS.=