401 
 WTNT41 KNHC 201451
 TCDAT1
 
 TROPICAL STORM FIONA DISCUSSION NUMBER  15
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
 1100 AM AST SAT AUG 20 2016
 
 Fiona is fighting off southwesterly shear this morning as the center
 has become embedded under the southwestern side of an area of deep
 convection.  The Dvorak estimates from TAFB and SAB have held
 steady, so the initial intensity is held at 35 kt.  Although a
 recent ASCAT overpass missed the center of Fiona, the pass did show
 30-kt winds more than 50 n mi east of the center, suggesting that
 tropical-storm-force winds could be occurring closer to the center
 of circulation. Strong southwesterly shear of 25 to 30 kt is
 forecast to persist during the next few days. These unfavorable
 conditions combined with dry air along the path of the cyclone
 should induce a gradual weakening trend, and Fiona is expected to
 weaken to a tropical depression by tonight or early Sunday morning.
 The ECMWF and UKMET models continue to open this system into a
 trough within 3 days, whereas, the other model guidance lessens the
 shear slightly toward the end of the 5-day period and allows Fiona
 to survive for the next several days. The official forecast is
 similar to the previous one, and leans toward the ECMWF and UKMET
 model solutions.
 
 The initial position of Fiona is located slightly to the north of
 the previous forecast track, based on recent microwave data. The
 track forecast reasoning remains unchanged, as the low- to mid-level
 subtropical ridge over the central Atlantic should keep Fiona moving
 west-northwestward for the next several days.  There remains a fair
 amount of spread in the guidance, which appears largely dependent
 on the future strength and status of the cyclone.  The NHC track
 forecast lies on the western side of guidance, except for the short
 term forecast positions where a slight adjustment to the north was
 made due to the initial position and motion.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  20/1500Z 20.3N  47.8W   35 KT  40 MPH
  12H  21/0000Z 21.2N  49.5W   35 KT  40 MPH
  24H  21/1200Z 22.3N  52.1W   30 KT  35 MPH
  36H  22/0000Z 23.3N  54.8W   30 KT  35 MPH
  48H  22/1200Z 24.2N  57.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
  72H  23/1200Z 26.2N  61.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
  96H  24/1200Z 28.2N  63.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 120H  25/1200Z...DISSIPATED
 
 $$
 Forecaster Cangialosi/Latto
 
 

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