Tropical Depression DON (Text)

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.

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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Page last modified: Monday, 18-Dec-2023 12:09:11 UTC