WTNT41 KNHC 200842 RRA

TCDAT1



TROPICAL STORM FIONA DISCUSSION NUMBER  14

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016

500 AM AST SAT AUG 20 2016



FIONA IS LOOKING RAGGED THIS MORNING WITH ONLY A SMALL AREA OF DEEP

CONVECTION ON THE NORTHERN SIDE OF THE APPARENT CENTER OF THE

CYCLONE. DVORAK ESTIMATES ARE A BIT LOWER THAN EARLIER, BUT I'VE

ELECTED TO KEEP FIONA A TROPICAL STORM FOR THIS ADVISORY GIVEN THE

EARLIER ASCAT DATA, PERHAPS GENEROUSLY. THE CYCLONE IS LIKELY TO

GRADUALLY WEAKEN FOR THE NEXT FEW DAYS WITH STRONG SHEAR, UPPER-

LEVEL CONVERGENCE, AND DRY MID-LEVEL AIR IN ITS PATH. AFTER

CONSIDERING THE UNFAVORABLE ENVIRONMENT AHEAD, THE NHC INTENSITY

FORECAST IS REDUCED FROM THE PREVIOUS ONE, AND NOW SHOWS FIONA AS A

REMNANT LOW IN 48 HOURS AND DISSIPATING BY DAY 5. THIS FORECAST

COULD BE CONSERVATIVE SINCE THE ECMWF AND UKMET NOW OPEN UP THIS

SYSTEM INTO A TROUGH WITHIN 3 DAYS.



THE INITIAL MOTION ESTIMATE IS ABOUT THE SAME AS BEFORE, 295/11,

MOSTLY BASED ON EXTRAPOLATION.  A SUBTROPICAL RIDGE OVER THE

CENTRAL ATLANTIC SHOULD KEEP FIONA MOVING WEST-NORTHWESTWARD FOR

THE NEXT FEW DAYS.  THE LONG-RANGE TRACK FORECAST REMAINS HIGHLY

CONTINGENT ON FIONA'S STATUS AS A TROPICAL CYCLONE, A REMNANT LOW,

OR A TROUGH.  A DEEPER CYCLONE WOULD LIKELY TAKE A MORE NORTHERN

TURN AT THE END OF THE PERIOD DUE TO A MID-LEVEL TROUGH, WHILE A

WEAKER CYCLONE WOULD PROBABLY JUST CONTINUE MOVING TO THE

WEST-NORTHWEST (AND NOT FEEL THE TROUGH).  SINCE THE CYCLONE IS NOW

EXPECTED TO BE A MORE SHALLOW SYSTEM IN A FEW DAYS, IT MAKES SENSE

TO BE ON THE WESTERN SIDE OF THE GUIDANCE ENVELOPE, WHICH REQUIRES

THE NEW NHC TRACK FORECAST TO BE SHIFTED LEFTWARD BEYOND DAY 2.=