[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 172040
TCDAT5

Tropical Depression Don Discussion Number  15
NWS National Hurricane Center Miami FL       AL052023
900 PM GMT Mon Jul 17 2023

GOES-16 visible imagery shows that Don is comprised of multiple
low-level swirls rotating around the larger circulation, which is
better defined than you might think at the surface based on earlier
scatterometer data.  Overall, the system is not well organized due
to persistent shear, dry air and marginal instability, with only a
distant burst of convection well east of the center.  There has been
no change with the latest satellite classifications, so the initial
wind speed remains 30 kt.

The environment around Don is forecast to become more conducive for
gradual intensification in a couple of days when the cyclone moves
over warmer waters with light-to-moderate shear, tempered by plenty
of mid-level dry air. Surprisingly, many of the recent regional
hurricane models show a hurricane forming over 24-25C waters in
several days time, which is hard to believe given the seemingly
marginal large-scale conditions.  Additionally, Don will have to
cross its own cool wake in 4-5 days, which isn't well accounted for
in the models yet.  The new forecast is bumped up at day 5 but
remains below the model consensus.

Don has turned southeastward at about 12 kt, in the process of
undergoing a large anticyclonic loop over the central Atlantic due
to a blocking ridge to its north.  The depression should begin to
gain latitude again late on Wednesday as the blocking ridge slides
eastward, and eventually Don should turn northwestward by the end of
the forecast period.  The biggest question remains how sharp of a
turn will occur late this week, with the ECMWF suite insisting on a
faster northward motion by the weekend, well east of the other
guidance.  An examination of those fields suggests that it doesn't
vertically redevelop Don as much as the rest of the guidance,
resulting in the cyclone not responding to the upper-level
southeasterly flow, and instead turning more quickly northward.
Since the new intensity forecast remains on the lower side of the
guidance envelope, the new NHC track forecast will also stay east of
the model consensus, not too different from the last prediction.



FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 38.1N  41.6W   30 KT  35 MPH
 12H  18/0600Z 37.1N  40.2W   30 KT  35 MPH
 24H  18/1800Z 35.4N  39.4W   30 KT  35 MPH
 36H  19/0600Z 34.3N  39.5W   30 KT  35 MPH
 48H  19/1800Z 33.6N  40.5W   35 KT  40 MPH
 60H  20/0600Z 33.8N  41.5W   35 KT  40 MPH
 72H  20/1800Z 34.4N  43.0W   40 KT  45 MPH
 96H  21/1800Z 36.7N  46.8W   45 KT  50 MPH
120H  22/1800Z 40.5N  50.0W   45 KT  50 MPH

$$
Forecaster Blake
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