Tropical Storm KATE (Text)

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.
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

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Page last modified: Friday, 31-Dec-2021 12:09:24 UTC