WTNT41 KNHC 210851 RRA

TCDAT1



TROPICAL STORM FIONA DISCUSSION NUMBER  18

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016

500 AM AST SUN AUG 21 2016



AFTER THE EARLIER CONVECTIVE BURSTING EPISODE AND RESULTANT SPIN UP

OF THE LOW-LEVEL WIND FIELD, STRONG WESTERLY SHEAR OF AT LEAST 30 KT

HAS STRIPPED AWAY THE CONVECTIVE CLOUD SHIELD, LEAVING A FULLY

EXPOSED LOW-LEVEL CIRCULATION CENTER THAT IS EASY TO LOCATE.

ASSUMING SOME SPIN DOWN OF THE CIRCULATION DUE TO THE LOSS OF

CONVECTION, THE INITIAL INTENSITY HAS BEEN LOWERED TO 40 KT.



NOW THAT FIONA'S CIRCULATION HAS BECOME A LITTLE MORE SHALLOW, THE

LOW-LEVEL CENTER HAS TURNED MORE WESTWARD AND THE CYCLONE IS NOW

MOVING 295/14 KT. THE GLOBAL MODELS ARE IN GOOD AGREEMENT ON A

MID-LEVEL RIDGE TO THE NORTH AND NORTHEAST OF FIONA REMAINING IN

PLACE FOR THE NEXT FEW DAYS, WHICH SHOULD KEEP THE SMALL CYCLONE

MOVING IN A GENERAL WEST-NORTHWEST DIRECTION THROUGH 72 HOURS. AFTER

THAT TIME, THE WESTERN PORTION OF THE RIDGE IS EXPECTED TO WEAKEN

DUE TO AN APPROACHING FRONTAL SYSTEM, WHICH SHOULD ALLOW FIONA OR

ITS REMNANT CIRCULATION TO SLOW DOWN AND TURN NORTHWESTWARD. THE NEW

TRACK FORECAST IS ESSENTIALLY JUST AN UPDATE OF THE PREVIOUS

ADVISORY TRACK, AND LIES CLOSE TO THE TVCN CONSENSUS MODEL FORECAST.



DURING THE NEXT 24 HOURS OR SO, FIONA IS FORECAST TO TRAVERSE

THROUGH A BAND OF STRONG WESTERLY TO NORTHWESTERLY VERTICAL WIND

SHEAR OF 25-30 KT AND DRY MID-LEVEL AIR WITH HUMIDITY VALUES NEAR 40

PERCENT. AS A RESULT, GRADUAL WEAKENING IS EXPECTED DUE TO THE SMALL

CYCLONE LIKELY NOT BEING ABLE TO SUSTAIN DEEP CONVECTION FOR LONG

PERIODS OF TIME. THE NEW INTENSITY FORECAST HOLDS ONTO THE PREVIOUS=