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Tropical Storm Darby Discussion Number   1
NWS National Hurricane Center Miami FL       EP052022
300 PM MDT Sat Jul 09 2022
 
The area of low pressure we have been monitoring well offshore the 
southwestern coast of Mexico has become much better organized on 
conventional satellite imagery throughout the day. The current 
structure on visible satellite imagery consists of a well-defined 
curved band to the north and west with what already appears to be a 
small central dense overcast forming near the estimated center. In 
fact, there is already a small dimple beginning to appear on the 
last few frames of visible satellite imagery which could be the 
initial indications that a small inner core is forming. While C-band 
scatterometer imagery (ASCAT-B/C) largely missed the small storm 
earlier today, there was a KU-band scatterometer late this morning 
that had enough non-rain contaminated vectors to indicate the system 
likely possesses a closed circulation. The subjective Dvorak 
classifications at 1800 UTC from TAFB/SAB were both T2.0/30 kt, but 
given the continued improvement on satellite imagery since then, 
advisories are being initiated on Tropical Storm Darby at this time, 
with winds of 35 kt.

The current motion of Darby is just north of due west at 280/14 kt. 
A general due westward motion is expected over the next 24-48 h as 
the small storm is situated on the south side of a expansive 
deep-layer subtropical ridge centered over the southwestern United 
States. Towards the end of the forecast period, Darby will be 
approaching a weakness in this ridge, which may allow the storm to 
start gaining latitude after 48 hours. The initial track forecast of 
Darby is very close to the reliable track consensus aids, though is 
just a shade further north, in deference to both the GFS and ECMWF 
forecasts.

The structure of Darby is quite impressive for a system that has 
only recently formed. In addition, both the GFS- and ECMWF-based 
SHIPS guidance indicate that the small storm will remain in a low 
shear (under 10 kt), warm sea-surface temperatures (above 28C), and 
sufficient mid-level moisture for the next 2-3 days. Assuming an 
inner core forms relatively soon, this environment likely favors 
quick intensification. In fact, the ECMWF SHIPS-RII guidance 
indicates a 44 percent chance of a 25 kt or higher increase in 
intensity over the next 24 hours. While the current NHC intensity 
forecast will not go that high quite yet, it does make Darby a 
hurricane in only 36 h. This intensity forecast is on the upper-end 
of the guidance envelope, but not far off the HFIP corrected 
consensus approach (HCCA) that is also near hurricane intensity in 
36 h. Late in the forecast, Darby will likely encounter cooler ocean 
waters and much higher shear, which should begin to induce weakening 
by the end of the forecast period.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/2100Z 14.3N 113.5W   35 KT  40 MPH
 12H  10/0600Z 14.4N 116.0W   45 KT  50 MPH
 24H  10/1800Z 14.5N 118.8W   55 KT  65 MPH
 36H  11/0600Z 14.4N 121.7W   65 KT  75 MPH
 48H  11/1800Z 14.4N 124.3W   75 KT  85 MPH
 60H  12/0600Z 14.6N 127.0W   80 KT  90 MPH
 72H  12/1800Z 15.0N 129.2W   80 KT  90 MPH
 96H  13/1800Z 16.2N 133.4W   65 KT  75 MPH
120H  14/1800Z 17.6N 138.4W   45 KT  50 MPH
 
$$
Forecaster Papin
 
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