424 
 WTNT45 KNHC 282055
 TCDAT5
 
 TROPICAL STORM ERIKA DISCUSSION NUMBER  16
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052015
 500 PM EDT FRI AUG 28 2015
 
 The low-level center of Erika continues to be be located west of
 the convection due to the impact of 25-30 kt of westerly vertical
 wind shear.  Satellite imagery and reports from an Air Force
 Reserve Hurricane Hunter aircraft indicate that the circulation has
 been losing definition during the day and it is now barely
 closed, at best.  However, clusters of strong convection continue in
 the eastern semicircle, and the initial intensity is held at 45 kt
 on the premise that the strong winds observed earlier are still
 present. The central pressure of 1009 mb is based on observations
 from the Dominican Republic.
 
 Erika has been moving more westward for the past several hours and
 the initial motion is 280/17.  There is no change to the forecast
 philosophy from the previous advisory.  A generally west-
 northwestward to northwestward motion is expected for the next 48
 hours or so as Erika moves around the southwestern periphery of the
 subtropical ridge. After that time, a northwestward and northward
 turn and a decrease in forward speed are forecast as Erika moves
 between the ridge and a mid- to upper-level trough over the Gulf of
 Mexico.  While the track guidance is generally in good agreement, it
 should be noted that the guidance has been consistently forecasting
 a west-northwestward turn that has so far failed to occur.  On the
 other hand, there is still a chance for a center to re-form
 farther to the north during the passage over Hispaniola.  So while
 the forecast track has been shifted west of the previous advisory,
 it still lies near the northern edge of the guidance envelope for
 the first 48 hours to maintain some continuity with the previous
 forecast. Additional adjustments may be necessary depending on how
 Erika evolves during the next 12-18 hours.
 
 The forecast intensity has been significantly changed to show a
 much weaker cyclone, with Erika now forecast to become a
 tropical depression in about 24 hours, followed by some slight
 intensification at 48 and 72 hours.  This represents a compromise
 between two scenarios.  The first is the increasing likelihood that
 Erika will degenerate to a tropical wave during the passage over
 Hispaniola, a scenario supported by the GFS, UKMET, and ECMWF
 models. The second acknowledges that the shear is still expected to
 subside after 36 hours and we're are not quite prepared to rule out
 tropical storm impacts in Florida.  The SHIPS and LGEM support this
 possibility.
 
 The greatest short-term threat posed by Erika continues to be very
 heavy rainfall over portions of the Dominican Republic and Haiti
 today and tonight. These rains could produce flash floods and mud
 slides.
 
 Although this would normally be an appropriate time for a tropical
 storm watch for portions of southern Florida, following typical
 timelines, we have elected to wait until we see what's left of
 Erika after it passes Hispaniola.  There is a significant chance
 that no watches or warnings for Florida will be required.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/2100Z 17.9N  71.2W   45 KT  50 MPH
  12H  29/0600Z 19.5N  73.5W   40 KT  45 MPH
  24H  29/1800Z 21.3N  76.5W   30 KT  35 MPH...INLAND
  36H  30/0600Z 22.7N  79.3W   30 KT  35 MPH...OVER WATER
  48H  30/1800Z 24.0N  81.0W   35 KT  40 MPH
  72H  31/1800Z 27.0N  82.5W   35 KT  40 MPH
  96H  01/1800Z 29.0N  82.5W   30 KT  35 MPH...INLAND
 120H  02/1800Z 31.0N  82.5W   25 KT  30 MPH...INLAND
 
 $$
 Forecaster Beven