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Hurricane Dorian Discussion Number  54
NWS National Hurricane Center Miami FL       AL052019
500 PM EDT Fri Sep 06 2019

Dorian has become better organized since it moved into the Atlantic
this morning, and satellite imagery shows that it now has a
well-defined eye embedded in a central dense overcast along with a
large outer banding feature in the northwestern semicircle.  The
last aircraft data near 1700 UTC indicated this had not yet resulted
in intensification.  However, the various subjective and objective
satellite intensity estimates are trending upward, and the advisory
intensity of 80 kt could be conservative.  The hurricane currently
has excellent outflow over the northern semicircle.

The initial motion is now 050/21.  Dorian should move quickly
northeastward during the next 24-48 h as it interacts with a mid- to
upper-level trough, currently over the eastern Great Lakes.  The
track guidance has changed little and remains tightly clustered, and
only minor adjustments have been made to the previous track.  The
new forecast track calls for Dorian to pass well southeast of
southern New England tonight and Saturday, and then move over Nova
Scotia Saturday or Saturday night.  A continued northeastward motion
is then expected to bring the cyclone across Newfoundland into the
far north Atlantic.

There has been a significant change to the intensity forecast
philosophy.  The GFS and ECMWF, which have been forecasting Dorian
to transition to a powerful extratropical low, now forecast
intensification of the system due to baroclinic processes associated
with the aforementioned trough, including very strong upper-level
divergence.  Given that Dorian is currently a well-organized
hurricane and will be south of the Gulf Stream for about the next
18-24 h, it is likely that at least some of this strengthening will
occur before Dorian becomes extratropical. The new intensity
forecast now calls for Dorian to strengthen as a hurricane during
the next 12-24 h, then undergo extratropical transition as it is
passing near or over Nova Scotia and Newfoundland.  The intensities
in the new forecast are increased during the first 24 h to reflect
this change.  Dorian is likely to be a hurricane at landfall in Nova
Scotia, but it will cause significant impacts even if it has
completed extratropical transition by that time.


Key Messages:

1. Life-threatening storm surge and dangerous winds will continue
along portions of the North Carolina coast for the next several
hours.

2. Regardless of whether Dorian is a hurricane or a post-tropical
cyclone, Dorian is expected to have a significant impact in portions
of eastern Canada.   Dangerous storm surge impacts are likely in
portions of the Gulf of St. Lawrence, southwestern Newfoundland and
eastern Nova Scotia this weekend. Hurricane-force winds are also
likely in Nova Scotia, Prince Edward Island and possibly
Newfoundland Saturday and Sunday.  Refer to information from the
Canadian Hurricane Centre for more information on these hazards.


FORECAST POSITIONS AND MAX WINDS

INIT  06/2100Z 36.9N  72.7W   80 KT  90 MPH
 12H  07/0600Z 39.1N  69.5W   85 KT 100 MPH
 24H  07/1800Z 42.9N  65.3W   85 KT 100 MPH
 36H  08/0600Z 47.1N  61.6W   70 KT  80 MPH
 48H  08/1800Z 50.6N  57.8W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  09/1800Z 55.5N  45.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  10/1800Z...DISSIPATED

$$
Forecaster Beven

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