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Tropical Depression Seventeen Forecast Discussion Number 1
2017-10-09 10:33:17| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Oct 09 2017 000 WTNT42 KNHC 090833 TCDAT2 Tropical Depression Seventeen Discussion Number 1 NWS National Hurricane Center Miami FL AL172017 500 AM AST Mon Oct 09 2017 The well-defined low pressure system over the eastern Atlantic several hundred miles southwest of the Azores has maintained an area of deep convection near and to the east of the center for the past several hours. Therefore, the system now meets the criteria for a tropical depression. The initial intensity is estimated to be 30 kt based on ASCAT data from around 0000 UTC and a 2.0/30 kt Dvorak classification from TAFB. The depression is moving slowly northward at 3 kt, and a continued slow north to north-northeast motion is expected today. A turn to the east and then southeast is forecast to begin tonight and continue through Wednesday while the cyclone is steered by the flow on the east side of a subtropical ridge. Thereafter, a mid- to upper-level trough is expected to approach the depression, and that should cause the system to move a little faster to the east and east-northeast. The NHC track forecast lies near the middle of the guidance envelope, in agreement with various consensus aids, and keeps the system far from any land areas. The depression is currently over marginally warm 27 deg C SSTs and in an environment of moderate to strong westerly shear. The models suggest that the shear will likely let up a little during the next couple of days, which could allow the depression to gradually strengthen while it remains over relatively warm waters. After that time, the shear could increase again, but the amount of shear depends on the exact track of the tropical cyclone. There is a fair amount of spread in the models at the longer range with the regional models (HWRF, HMON, and COAMPS-TC) bringing the system to hurricane strength while the statistical SHIPS and LGEM models show a much weaker system. The NHC intensity forecast leans toward the more conservative side of the guidance for now, but it should be noted that confidence in the intensity forecast is low. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 31.1N 39.9W 30 KT 35 MPH 12H 09/1800Z 31.5N 39.8W 35 KT 40 MPH 24H 10/0600Z 31.7N 39.0W 35 KT 40 MPH 36H 10/1800Z 31.5N 38.4W 40 KT 45 MPH 48H 11/0600Z 31.0N 37.8W 45 KT 50 MPH 72H 12/0600Z 29.7N 37.0W 50 KT 60 MPH 96H 13/0600Z 29.7N 35.5W 50 KT 60 MPH 120H 14/0600Z 31.0N 32.0W 50 KT 60 MPH $$ Forecaster Cangialosi
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