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Tropical Storm Kate Forecast Discussion Number 10
2021-08-30 16:55:30| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Aug 30 2021 000 WTNT45 KNHC 301455 TCDAT5 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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