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Tropical Storm Dorian Discussion Number   4
NWS National Hurricane Center Miami FL       AL052019
500 AM AST Sun Aug 25 2019

The convective organization of Dorian is about the same as it was
several hour ago with the storm only producing small, generally
short-lived thunderstorm areas.  GOES-16 1-minute satellite images
have been particularly helpful in locating the center in between
bands of convection to the north and south of the cyclone.  The
initial wind speed is kept at 35 kt based on the most recent TAFB
Dvorak fix.

Dorian continues moving westward or 280/11 kt.  A west to
west-northwestward course of the tropical cyclone is expected during
the next several days as a mid-level ridge remains in place over
the southwestern Atlantic Ocean.  There has been a noticeable
change in the guidance tonight, with many models faster and to the
southwest of earlier runs.  This is not uncommon in the early
stages of tropical Atlantic cyclones where the guidance has
historically demonstrated a slow, poleward bias.  Given the lack of
interaction with even features at the subtropical latitudes, it
makes sense to follow the trend of the latest guidance and shift the
track about 30 n mi southwest during most of the forecast. Notably,
the GFS and ECMWF models are still south of the new NHC prediction,
and further adjustments could be required later today.

The intensity forecast appears to be a battle between an
increasingly conducive oceanic and shear environment during the
next couple of days versus plentiful dry air in the mid-levels of
the atmosphere.  These mixed conditions primarily point toward slow
strengthening during that time while Dorian approaches the Windward
Islands, and no change has been made to the first part of the
forecast.  While Dorian still has a chance to become a hurricane
over the eastern Caribbean, model guidance has been trending toward
a higher-shear environment caused by a large upper low in a few
days. Thus the intensity forecast is reduced from the previous one
at long range, although it remains above most of the guidance.  It
should be stressed that Dorian is likely to be a difficult cyclone
to forecast due to the marginal environment it is embedded within
and its small size.


Key Messages:

1.  A Tropical Storm Watch has been issued for Barbados, and
additional watches and warnings for the Windward and Leeward Islands
will likely be required later today.

2. It is too soon to determine the specific timing or magnitude of
impacts in Puerto Rico or Hispaniola, but interests in those areas
should monitor the progress of Dorian.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 11.0N  51.6W   35 KT  40 MPH
 12H  25/1800Z 11.3N  53.3W   40 KT  45 MPH
 24H  26/0600Z 11.8N  55.5W   45 KT  50 MPH
 36H  26/1800Z 12.4N  57.7W   50 KT  60 MPH
 48H  27/0600Z 13.2N  59.9W   55 KT  65 MPH
 72H  28/0600Z 15.2N  63.9W   65 KT  75 MPH
 96H  29/0600Z 17.1N  67.6W   60 KT  70 MPH
120H  30/0600Z 19.5N  71.0W   35 KT  40 MPH...INLAND

$$
Forecaster Blake

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