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Tropical Storm Kate Discussion Number  10
NWS National Hurricane Center Miami FL       AL102021
1100 AM AST Mon Aug 30 2021
 
Although strong upper-level westerly shear continues to plague the 
cyclone, its satellite presentation improved early this morning as 
its center moved closer to the edge of the convective cloud mass to 
its east. An ASCAT-A pass from 1100 UTC revealed an area of 30 to 
40-kt winds in the eastern semicircle of the cyclone, with some 
slightly stronger winds possibly rain contaminated underneath the 
deep convection. Additionally, UW-CIMSS ADT objective estimates have 
risen to around 40 kt within the past few hours, and TAFB gave a 
T2.5/35 kt subjective Dvorak classification at 12 UTC. These data 
support upgrading the depression to Tropical Storm Kate. Its initial 
intensity is set at 40 kt for this advisory, although that could be 
a bit generous given recent satellite trends.
 
A weakness in the subtropical ridge is allowing Kate to move just 
west of due north, or 355/7 kt. This general motion should continue 
for the next day or so before the subtropical ridge becomes 
reestablished over the central Atlantic Ocean. Thereafter, the 
cyclone should move northwestward on Wednesday and Thursday along 
the southwestern periphery of the ridge. By Friday, an approaching 
deep-layer trough should cause the cyclone to accelerate northward 
or north-northeastward through the rest of the forecast period. The 
track guidance has shifted a little left of the previous NHC track, 
and so the official forecast has been adjusted in that direction to 
bring it closer to the TVCA and HCCA consensus aids.
 
The near-term intensity forecast is tricky, as the subtropical jet 
stream will maintain strong west-northwesterly shear over Kate 
during the next 24 to 36 h. In fact, recent satellite imagery of the 
cyclone shows the center is already more exposed than earlier this 
morning as the convection is waning. Kate is likely to continue 
exhibiting a bursting convective pattern over the next couple of 
days, which would likely result in some intensity fluctuations that 
hover around the tropical-storm-force threshold. The official NHC 
intensity forecast shows Kate as a 35-kt tropical storm during the 
first 36 h of the forecast. If Kate survives the hostile shear 
conditions, some modest intensification will be possible while the 
cyclone remains over 28 deg C waters. However, Kate will encounter a 
drier mid-level environment as it gains latitude, so significant 
strengthening does not appear likely at this time. The official 
intensity forecast is similar to the previous one beyond 48 h, as it 
shows only modest strengthening with time. By day 5, the global 
models suggest that Kate could be becoming absorbed by a larger 
extratropical low expected to form and deepen near Atlantic Canada.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/1500Z 21.5N  50.9W   40 KT  45 MPH
 12H  31/0000Z 22.3N  50.7W   35 KT  40 MPH
 24H  31/1200Z 23.3N  50.5W   35 KT  40 MPH
 36H  01/0000Z 24.3N  50.6W   35 KT  40 MPH
 48H  01/1200Z 25.5N  51.5W   40 KT  45 MPH
 60H  02/0000Z 26.9N  52.7W   40 KT  45 MPH
 72H  02/1200Z 28.4N  54.2W   45 KT  50 MPH
 96H  03/1200Z 32.0N  55.5W   50 KT  60 MPH
120H  04/1200Z 37.0N  53.4W   55 KT  65 MPH
 
$$
Forecaster Reinhart
 
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