WTNT41 KNHC 210249 RRA

TCDAT1



TROPICAL STORM FIONA DISCUSSION NUMBER  17

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016

1100 PM AST SAT AUG 20 2016



SOMEWHAT SURPRISINGLY, TWO RECENT ASCAT PASSES SHOWED THAT FIONA IS

PRODUCING 45-KT WINDS IN ITS NORTHEASTERN QUADRANT.  THIS INTENSITY

IS ALSO SUPPORTED BY THE LATEST ADT ESTIMATE.  DESPITE THE INCREASE

IN MAXIMUM WINDS, THE NEXT 36 HOURS WILL BE CRITICAL FOR FIONA'S

SURVIVAL AS A TROPICAL CYCLONE.  DURING THIS PERIOD, WESTERLY SHEAR

OF 30 KT WILL BE AT ITS STRONGEST, AND MID-LEVEL RELATIVE HUMIDITIES

WILL BE AT THEIR LOWEST.  THEREFORE, GRADUAL WEAKENING IS

ANTICIPATED, AND IT'S ENTIRELY POSSIBLE THAT FIONA COULD SOON

STRUGGLE TO MAINTAIN ORGANIZED DEEP CONVECTION.  FOR NOW, THE NHC

OFFICIAL FORECAST SHOWS FIONA BECOMING A REMNANT LOW BY 72 HOURS.

HOWEVER, THERE IS A LOT OF UNCERTAINTY IN THIS FORECAST.  IF FIONA

CAN SURVIVE THE NEXT 36 HOURS, IT MIGHT PERSIST AS A WEAK TROPICAL

CYCLONE THROUGH THE END OF THE FORECAST PERIOD SINCE ENVIRONMENTAL

CONDITIONS DO BECOME A LITTLE MORE FAVORABLE IN A COUPLE OF DAYS. IT

SHOULD BE NOTED THAT MOST OF THE GLOBAL MODELS HANG ONTO A WEAK LOW

FOR AT LEAST THE NEXT 5 DAYS, WITH THE EXCEPTION OF THE ECMWF WHICH

SHOWS THE LOW OPENING UP INTO A TROUGH BY 48 HOURS.  FOR NOW, THE

NHC FORECAST CONTINUES TO SHOW DISSIPATION BY DAY 5 AS A COMPROMISE.



FIONA'S MOTION HAS BEEN WAVERING BETWEEN WEST-NORTHWEST AND

NORTHWEST, AND THE LATEST ESTIMATE IS 305/13 KT.  LOW-LEVEL RIDGING

SHOULD KEEP FIONA ON THIS GENERAL TRAJECTORY FOR THE NEXT 72 HOURS

OR SO, FOLLOWED BY A NORTHWESTWARD TURN WITH A DECREASE IN SPEED BY

DAY 4 WHEN THE CYCLONE APPROACHES A STALLED FRONTAL BOUNDARY OFF=