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Hurricane Darby Discussion Number  13
NWS National Hurricane Center Miami FL       EP052022
500 AM HST Tue Jul 12 2022
 
While Darby remains an impressively compact hurricane, there has
been a bit of erosion in the inner-core convective structure this
morning. The eye in particular has become less distinct and has
cooled relative to yesterday afternoon, though the eyewall
convection remains strong and quite circular. While an AMSR2
microwave pass at 1042 UTC still showed a closed eyewall, the
convection on the northwestern side has eroded some compared to
yesterday. Darby remains a very small tropical cyclone, with
overnight scatterometer wind data indicating tropical-storm-force
winds extend out to 40 n mi to the northeast of the center. While
the latest TAFB/SAB Dvorak classifications were a consensus CI
6.0/115 kt, the objective ADT and SATCON data is quite a bit lower.
The initial intensity on this advisory is set at 110 kt, blending
the guidance, but favoring the somewhat higher subjective Dvorak
estimates.
 
While the current vertical wind shear (VWS) over Darby remains very 
low, sea-surface temperatures underneath the hurricane are gradually 
decreasing, now currently just under 27 C. It seems likely that 
Darby is now post-peak intensity and should begin to gradually 
weaken in the short-term under the less favorable thermodynamic 
environment. After 24 hours, a combination of an increasingly stable 
and dry airmass, plus an increase in southwesterly VWS from a broad 
upper-level trough to the northwest of Darby, is expected to lead to 
a more rapid weakening trend later this week. The latest NHC 
intensity forecast is still on the high side of the guidance 
envelope early on, but then shows a faster rate of weakening as the 
small cyclone encounters a more hostile environment. Darby is still 
expected to become post-tropical by 96 hours as deep convection is 
completely removed from the center and dissipates as suggested by 
the GFS and ECMWF models at that period.
 
Darby continues to move on a due westward heading at 270/14 kt.
There is not much new to report with the track philosophy, as a
mid-level ridge currently north of Darby will be eroded some by the
aforementioned upper-level trough. This should result in a bit more
west-northwest bend in Darby's track between 24-60 hours. After that
period, Darby is expected to become an increasingly shallow vortex,
and its track should turn back westward following the trade-wind
flow around a large low-level subtropical ridge poleward of
Hawaii. The latest track forecast is little changed from the prior
advisory, and remains close to the tightly clustered consensus aids.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/1500Z 14.7N 129.7W  110 KT 125 MPH
 12H  13/0000Z 14.8N 131.7W  105 KT 120 MPH
 24H  13/1200Z 15.2N 134.4W  100 KT 115 MPH
 36H  14/0000Z 15.8N 137.0W   85 KT 100 MPH
 48H  14/1200Z 16.4N 139.5W   75 KT  85 MPH
 60H  15/0000Z 16.9N 142.0W   60 KT  70 MPH
 72H  15/1200Z 17.2N 144.6W   45 KT  50 MPH
 96H  16/1200Z 17.1N 150.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  17/1200Z...DISSIPATED
 
$$
Forecaster Papin
 
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