Tropical Storm KATE Advisory mar, 31-08

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Tropical Storm Kate Discussion Number  13
NWS National Hurricane Center Miami FL       AL102021
500 AM AST Tue Aug 31 2021

Kate remains a strongly sheared tropical storm with the associated
deep convection occurring in intermittent bursts in the eastern
semicircle of the cyclone, owing to 850-200-mb west-northwesterly
vertical wind shear of at least 30 kt. The most recent Dvorak
satellite current intensity (CI) estimates remain at 35 kt, and
that is the initial intensity set for this advisory. This intensity
is consistent with an earlier SSMI-S passive microwave satellite
overpass that showed wind speeds of 30-35 kt on the west side of
Kate where no convection/rain was present.

The initial motion estimate is 360/04 kt.  Kate's forward motion has
slowed to as low 2 kt during the psst 6 hours, likely due to the
hindering effects of the west-northwesterly shear direction and weak
steering currents since Kate has recently moved into a weakness in
the low- mid-level subtropical ridge. However, the latest NHC track
guidance is in good agreement that the cyclone will begin moving
northward at a slightly faster forward speed as Kate moves through
a break in the ridge. In about 24 hours, a mid-level ridge to the
northeast and east of Kate is forecast to build westward, forcing
the cyclone on a more northwestward trajectory that should continue
through Thursday. By Friday, a mid- to upper-level trough moving
eastward over the western Atlantic is forecast to gradually lift out
Kate toward the north, and accelerate the cyclone toward the
northeast on Saturday. The new NHC forecast track is similar to but
slightly east or right of the previous advisory track, and lies near
the left edge of the tightly packed simple- and corrected-consensus
track-model envelope.

The intensity forecast is not as straightforward as the track
forecast. The aforementioned hostile shear conditions are predicted
by the regional and global models, especially the ECMWF model, to
gradually abate over the next 18-24 hours, with the magnitude of the
shear to decrease to less than 10 kt by 24-36 hours when Kate will
be moving over 28.5 deg C water temperatures. If Kate can survive
the next 18 hours or so, which is possible since the 850-300-mb
shear is much less at only 10-15 kt, then some restrengthening could
occur, especially in the 24-48-hour period when the cyclone will be
located underneath a small upper-level anticyclone. Countering that,
however, is the somewhat dry air (near-50-percent humidity) in the
mid-levels of the atmosphere that could limit the formation of
inner-core convection. Thus for now, the new official intensity
forecast remains similar to the previous advisory, which shows Kate
remaining as a low-end tropical storm through the 96-hour period.
This scenario is consistent with the IVCN and HCCA intensity
consensus models. On day 5, Kate is forecast to dissipate when the
cyclone or its remnants are expected to merge with an extratropical
low and associated frontal system.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 23.0N  50.9W   35 KT  40 MPH
 12H  31/1800Z 23.9N  50.9W   35 KT  40 MPH
 24H  01/0600Z 25.2N  51.5W   35 KT  40 MPH
 36H  01/1800Z 26.6N  52.4W   35 KT  40 MPH
 48H  02/0600Z 28.3N  53.4W   35 KT  40 MPH
 60H  02/1800Z 29.9N  54.2W   35 KT  40 MPH
 72H  03/0600Z 31.5N  54.8W   35 KT  40 MPH
 96H  04/0600Z 35.1N  53.6W   35 KT  40 MPH
120H  05/0600Z...DISSIPATED

$$
Forecaster Stewart