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Tropical Depression THREE


Tropical Depression Three Discussion Number   3
NWS National Hurricane Center Miami FL       AL032018
500 AM EDT Sat Jul 07 2018

A pair of late-arriving ASCAT passes at 0136 UTC and 0216 UTC
revealed the the depression has not yet strengthened, and its
circulation remains very broad.  Although the larger-scale
circulation of the cyclone is well-defined, it lacks an inner core,
and the center of circulation consists of a wide area of light
winds.  The initial intensity has been held at 25 kt based primarily
on the ASCAT data, and this is also supported by the latest Dvorak
classifications from TAFB and SAB.

While the cyclone was nearly devoid of deep convection for several
hours late last night and early this morning, a broken convective
band has since developed to the south of the low-level center.  This
could indicate that the depression is beginning to become better
organized and will begin to slowly strengthen.  Warm SSTs will
likely allow the depression to gradually strengthen through the next
3 to 4 days, however moderate shear and the lack of an existing
inner-core will likely limit the intensification rate.  The
intensity guidance has come into better agreement since yesterday,
and now most of the models show the cyclone nearing or reaching
hurricane strength. No change has been made to the NHC intensity
forecast, which is now near the middle of the guidance and very
close to HCCA throughout the forecast.

Nighttime Proxy-Vis imagery has been very helpful in tracking the
depression this morning, which has slowed down and is now estimated
to be moving north-northwestward or 345/4 kt.  For the first 48 h,
the track models remain in fairly good agreement that the cyclone
will meander off the coast of the Carolinas, as it becomes trapped
in the light steering flow between a cold front passing to the north
and the subtropical ridge to the east.  Beyond that time, there has
been a significant change in the track models, all of which now
depict a much faster northeastward motion beginning on Tuesday as
the cyclone recurves ahead of a mid-level trough approaching from
the northwest. Although the NHC track forecast has been adjusted to
show a faster motion at day 4 and 5, it is now much slower than all
of the global models in an effort to maintain continuity from our
earlier forecasts.  If this trend continues, larger changes will
need to be made to the track forecast in future advisories.

Most of the guidance continues to suggest that the
tropical-storm-force winds associated with the cyclone will occur
primarily to the east of the cyclone's center well away from the
U.S. coast.  Therefore, no watches or warnings are required for the
U.S coast at this time, however, interests along the North Carolina
coast should monitor the progress of this system.


INIT  07/0900Z 33.2N  74.6W   25 KT  30 MPH
 12H  07/1800Z 33.6N  74.8W   30 KT  35 MPH
 24H  08/0600Z 33.8N  74.5W   35 KT  40 MPH
 36H  08/1800Z 33.9N  74.0W   40 KT  45 MPH
 48H  09/0600Z 34.0N  73.6W   45 KT  50 MPH
 72H  10/0600Z 34.5N  72.5W   55 KT  65 MPH
 96H  11/0600Z 37.0N  69.0W   65 KT  75 MPH
120H  12/0600Z 41.0N  63.5W   65 KT  75 MPH

Forecaster Zelinsky