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Tropical Depression Kate Forecast Discussion Number 18
2021-09-01 17:00:05| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 01 2021 448 WTNT45 KNHC 011459 TCDAT5 Tropical Depression Kate Discussion Number 18 NWS National Hurricane Center Miami FL AL102021 1100 AM AST Wed Sep 01 2021 It has been difficult to pinpoint where the low-level circulation of Kate is this morning. After last night's diurnal convective maximum, the remaining convection has taken on a very disorganized structure, with a mid-level vortex being left behind to the south, while deeper, but more outflow driven convection is racing off to the north, ahead of the estimated low-level center position. A recently received 1211 UTC ASCAT-A pass indicated that Kate's low-level circulation is still closed, but just barely. The scatterometer wind data supports maintaining the current intensity at 30-kt, which also agrees with the latest subjective and objective Dvorak estimates. The estimated motion is continuing off to the north-northwest, at 340/9 kt. Kate appears to now be primarily steered by the low-level flow around a subtropical ridge located to its east. A general north-northwest motion is expected to continue today, followed by a turn to the north and north-northeast around the periphery of this ridge. The latest NHC track guidance has been adjusted a bit right of the previous track, shifting towards the latest consensus guidance (TVCN) that can still track the cyclone beyond 24 hours. A 0958 UTC SSMIS microwave pass suggested that the better organized structure observed last night has decayed, with the low- and mid-level centers quite misaligned. Vertical wind shear diagnosed by SHIPS is now between 15-20 kt out of the north. This shear is likely contributing to the vortex tilt, while also helping to import very dry mid-level air, preventing Kate's convective activity from organizing. The bulk of the intensity guidance is in agreement that gradual spin down of the low-level circulation will occur over the next several days, with the deterministic ECMWF model suggesting Kate could open up to a trough as soon as tomorrow. The latest NHC intensity forecast makes Kate a remnant low in 36 hours, with dissipation after 48 hours. However, given the current structure, this could occur sooner than forecast. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 26.8N 52.3W 30 KT 35 MPH 12H 02/0000Z 27.9N 52.7W 25 KT 30 MPH 24H 02/1200Z 29.6N 53.1W 25 KT 30 MPH 36H 03/0000Z 31.1N 53.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 03/1200Z 32.4N 52.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 04/0000Z...DISSIPATED $$ Forecaster Papin
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