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Tropical Depression Ten Forecast Discussion Number 5
2021-08-29 10:56:29| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Aug 29 2021 034 WTNT45 KNHC 290856 TCDAT5 Tropical Depression Ten Discussion Number 5 NWS National Hurricane Center Miami FL AL102021 500 AM AST Sun Aug 29 2021 Tropical Depression Ten continues to struggle against 25-30 kt of northwesterly vertical wind shear, as diagnosed by the latest SHIPS guidance. Convection has thus remained displaced primarily to the southeast, though with some recent cells trying to develop closer to the center. The most recent TAFB and SAB Dvorak estimates were T2.5/35 kt and T2.0/30 kt with the objective ADT estimate at T2.3/33 kt. Given the disorganized nature of the current structure on IR satellite, I have elected to stay on the conservative side of these estimates and hold the intensity at 30 kt for this advisory. The depression continues to move toward the north at 360/9 kt. A large weakness in the mid-level ridging, due to a strong upper-tropospheric trough, will allow the depression to continue moving northward in the short-term, though there may be some occasional eastward bends as downshear convection tugs at the low-level vortex of the system. However by 72 h, some mid-level ridging is expected to build back in, allowing the track to shift a bit more leftward to the north-northwest after this point. The track guidance has not shifted much over the forecast period, and the latest NHC track forecast is nearly on top of the previous one, continuing to favor a blend of the the consensus aids (HCCA, TVCN). The poor current structure of the depression, under high shear importing dry air, argues against much short term intensification. However, the ECMWF-SHIPS guidance still suggests a brief respite in the shear between 12-24 hours. For this reason, the NHC intensity forecast still shows some slight strengthening to a tropical storm in 24 hours. Another round of 25-30 kt of vertical wind shear between 24-48 hours is then expected to keep the system in check, and it remains possible that the cyclone could degenerate to a remnant low over this time period. However, by 72 hours, the upper-level trough shearing the system is forecast to cut-off to the southwest, and this will shift the upper-level flow from northwesterly to southeasterly, which should provide a more favorable environment for strengthening. Thus, gradual strengthening is shown beginning in 72 hours extending through the end of the forecast. The latest NHC intensity forecast is quite similar to the previous forecast, favoring the more pessimistic ECMWF guidance versus the more aggressive GFS and regional hurricane models. There is quite a bit of uncertainty in the latter portion of this forecast since it is unclear how much of the cyclone will survive the current unfavorable environment during the next 2-3 days. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 17.3N 49.8W 30 KT 35 MPH 12H 29/1800Z 18.4N 49.8W 30 KT 35 MPH 24H 30/0600Z 19.9N 49.8W 35 KT 40 MPH 36H 30/1800Z 21.4N 49.4W 35 KT 40 MPH 48H 31/0600Z 22.7N 48.9W 35 KT 40 MPH 60H 31/1800Z 24.0N 48.9W 35 KT 40 MPH 72H 01/0600Z 25.6N 49.3W 40 KT 45 MPH 96H 02/0600Z 29.0N 50.5W 45 KT 50 MPH 120H 03/0600Z 32.0N 51.0W 50 KT 60 MPH $$ Forecaster Papin
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