Issued at 500 PM AST Thu Sep 12 2024
000 WTNT42 KNHC 122022 TCDAT2 Tropical Depression Seven Discussion Number 6 NWS National Hurricane Center Miami FL AL072024 Issued by the NWS Weather Prediction Center College Park MD 500 PM AST Thu Sep 12 2024 Tropical Depression Seven appears somewhat more organized on satellite imagery this afternoon, with a compact circulation and a couple bursts of deeper convection near the center, though it has been exposed for portions of the day. Subjective and objective Dvorak numbers indicate the system is close to becoming a tropical storm. However, the initial intensity will stay 30 kt, at the lower end of the estimates, until we get a little more definitive evidence of a tropical storm. The cyclone continues on a west-northwestward heading, and the general motion is expected to continue over the next 2-3 days. The forward speed should gradually slow as the subtropical ridge to the north of the system weakens. Track guidance diverges considerably early next week, related to uncertainties with an amplifying trough over the north-central Atlantic Ocean and another ridge centered northeast of the Leeward Islands. The GFS-based guidance has trended much farther west and faster, showing a weakening system at long range. However, the ECMWF and its ensemble members still show a risk of a stronger system, so the forecast will stay on the northeastern side of the track guidance. The new NHC forecast is faster and left of the previous one owing to the bulk of the guidance shifts during this cycle. While environmental conditions are somewhat favorable for gradual strengthening, with low-moderate vertical wind shear and marginally warm SSTs, intensity guidance is even lower than the last cycle. Slight strengthening seems most probable within the marginal environment, and the forecast continues to show a 45-kt peak in 5 days. There is also the potential for greater strengthening beyond what is shown early next week as the cyclone will be in an environment characterized by lower shear, warmer SSTs around 28C, slightly more instability, but plentiful dry air aloft. The latest intensity forecast is very similar to the previous one, on the high side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 18.3N 35.9W 30 KT 35 MPH 12H 13/0600Z 18.9N 37.6W 35 KT 40 MPH 24H 13/1800Z 19.4N 39.8W 35 KT 40 MPH 36H 14/0600Z 19.7N 41.5W 35 KT 40 MPH 48H 14/1800Z 19.8N 43.1W 40 KT 45 MPH 60H 15/0600Z 19.9N 44.5W 40 KT 45 MPH 72H 15/1800Z 19.8N 46.1W 40 KT 45 MPH 96H 16/1800Z 19.8N 48.4W 40 KT 45 MPH 120H 17/1800Z 20.3N 50.0W 45 KT 50 MPH $$ Forecaster Hurley/Blake
