Tropical Storm KATE Advisory dom, 29-08

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Tropical Depression Ten Discussion Number   5
NWS National Hurricane Center Miami FL       AL102021
500 AM AST Sun Aug 29 2021

Tropical Depression Ten continues to struggle against 25-30 kt of
northwesterly vertical wind shear, as diagnosed by the latest SHIPS
guidance. Convection has thus remained displaced primarily to the
southeast, though with some recent cells trying to develop closer to
the center. The most recent TAFB and SAB Dvorak estimates were
T2.5/35 kt and T2.0/30 kt with the objective ADT estimate at T2.3/33
kt. Given the disorganized nature of the current structure on IR
satellite, I have elected to stay on the conservative side of these
estimates and hold the intensity at 30 kt for this advisory.

The depression continues to move toward the north at 360/9 kt. A
large weakness in the mid-level ridging, due to a strong
upper-tropospheric trough, will allow the depression to continue
moving northward in the short-term, though there may be some
occasional eastward bends as downshear convection tugs at the
low-level vortex of the system. However by 72 h, some mid-level
ridging is expected to build back in, allowing the track to shift a
bit more leftward to the north-northwest after this point. The track
guidance has not shifted much over the forecast period, and the
latest NHC track forecast is nearly on top of the previous one,
continuing to favor a blend of the the consensus aids (HCCA, TVCN).

The poor current structure of the depression, under high shear
importing dry air, argues against much short term intensification.
However, the ECMWF-SHIPS guidance still suggests a brief respite in
the shear between 12-24 hours. For this reason, the NHC intensity
forecast still shows some slight strengthening to a tropical storm
in 24 hours. Another round of 25-30 kt of vertical wind shear
between 24-48 hours is then expected to keep the system in check,
and it remains possible that the cyclone could degenerate to a
remnant low over this time period. However, by 72 hours, the
upper-level trough shearing the system is forecast to cut-off to the
southwest, and this will shift the upper-level flow from
northwesterly to southeasterly, which should provide a more
favorable environment for strengthening. Thus, gradual
strengthening is shown beginning in 72 hours extending through the
end of the forecast. The latest NHC intensity forecast is quite
similar to the previous forecast, favoring the more pessimistic
ECMWF guidance versus the more aggressive GFS and regional hurricane
models. There is quite a bit of uncertainty in the latter portion of
this forecast since it is unclear how much of the cyclone will
survive the current unfavorable environment during the next 2-3
days.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 17.3N  49.8W   30 KT  35 MPH
 12H  29/1800Z 18.4N  49.8W   30 KT  35 MPH
 24H  30/0600Z 19.9N  49.8W   35 KT  40 MPH
 36H  30/1800Z 21.4N  49.4W   35 KT  40 MPH
 48H  31/0600Z 22.7N  48.9W   35 KT  40 MPH
 60H  31/1800Z 24.0N  48.9W   35 KT  40 MPH
 72H  01/0600Z 25.6N  49.3W   40 KT  45 MPH
 96H  02/0600Z 29.0N  50.5W   45 KT  50 MPH
120H  03/0600Z 32.0N  51.0W   50 KT  60 MPH

$$
Forecaster Papin