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Tropical Depression THIRTEEN Forecast Discussion Number 3
2016-09-20 10:42:16| National Hurricane Center (Atlantic)
Issued at 500 AM AST TUE SEP 20 2016 000 WTNT43 KNHC 200841 TCDAT3 TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 AM AST TUE SEP 20 2016 The cloud pattern of the depression is only slightly better organized than yesterday, with some broken convective banding over the northeastern portion of the circulation. Overall, however, the system is elongated from southwest to northeast. The initial intensity is held at 30 kt, in agreement with Dvorak estimates from both TAFB and SAB. The tropical cyclone is expected to remain in a low shear environment for the next 48 hours or so, and therefore some strengthening is forecast during that time frame. Later in the period, the dynamical environment is likely to become hostile for strengthening since shear associated with an upper-level trough is forecast to increase to around 30 kt in 3-4 days. Given this expected change in the large-scale environment, weakening should begin in 2-3 days and the system is predicted to revert to tropical depression status by the end of the forecast period. Although the dynamical guidance shows some relaxation of the shear at the end of the period, the current thinking is that by that time the system will be too disrupted to be able to recover. The official intensity forecast is close to the LGEM guidance through 72 hours and a little below it at days 4 and 5. There is considerable spread in center fixes and the initial motion is an uncertain 295/8 kt. A weakness in the subtropical ridge along 30W-40W is likely to induce a more northwestward track during the next day or so, followed by a return to a west- northwestward motion as the ridge rebuilds a bit to the north of the cyclone. Late in the forecast period, the system is forecast to turn back toward the northwest due to another weakness in the ridge. The official track forecast is somewhat slower and to the right of the previous one but close to the new dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 14.4N 29.6W 30 KT 35 MPH 12H 20/1800Z 15.4N 30.7W 35 KT 40 MPH 24H 21/0600Z 16.6N 32.2W 40 KT 45 MPH 36H 21/1800Z 17.5N 34.0W 45 KT 50 MPH 48H 22/0600Z 18.4N 35.8W 50 KT 60 MPH 72H 23/0600Z 20.8N 38.3W 45 KT 50 MPH 96H 24/0600Z 23.4N 40.6W 35 KT 40 MPH 120H 25/0600Z 26.5N 43.5W 30 KT 35 MPH $$ Forecaster Pasch
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