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| #873195 (Received by flhurricane at: 4:59 PM 28.Aug.2016) TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 500 PM EDT SUN AUG 28 2016 Data from a NOAA Hurricane Hunter aircraft indicate that the area of low pressure located in the Florida Straits now has a well-defined center. Satellite imagery shows a significant increase in the convective organization today, and as a result the system is now classified as a tropical cyclone. The initial intensity is set to 30 kt based on the highest believable wind data from the aircraft, which reported a central pressure of 1009 mb. The depression will be moving through a marginal environment for intensification during the next day or so, with vertical shear of 15 to 20 kt. As a result only slow strengthening is expected in the short term. Later on, the environment may improve a little as the shear is forecast to decrease somewhat and become southwesterly, which should allow for a little more strengthening. However, there are mixed signals in the model guidance, with the ECMWF now showing the cyclone dissipating in the Gulf, while the GFS delays development until 4-5 days. Much of the tropical cyclone guidance is more aggressive. Given this uncertainty, the NHC intensity forecast is quite conservative and shows the system peaking at 45 kt, below all the explicit intensity guidance in consideration of the negative signal from the ECMWF. Needless to say, the confidence in the intensity forecast is even lower than usual for this system. The initial motion estimate is an uncertain 270/09 given the recent formation of the center. The cyclone will be steered in the short range by a mid-level ridge centered over the southeastern United States. This ridge will weaken in 2-3 days, which will cause the cyclone to slow down and turn northward during this time. Late in the period a northeastward acceleration is expected ahead of an approaching mid-latitude trough. There is reasonable agreement in the track of the cyclone in the global model guidance, although there is a fair bit of along-track spread late in the period. The NHC forecast is close to a consensus of the GFS and ECMWF through day 4 and is a little faster than the GFS and GEFS ensemble mean at day 5. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 23.7N 81.7W 30 KT 35 MPH 12H 29/0600Z 23.9N 83.6W 30 KT 35 MPH 24H 29/1800Z 24.3N 85.4W 35 KT 40 MPH 36H 30/0600Z 24.6N 86.8W 35 KT 40 MPH 48H 30/1800Z 25.1N 87.6W 40 KT 45 MPH 72H 31/1800Z 26.8N 87.4W 45 KT 50 MPH 96H 01/1800Z 29.0N 84.5W 45 KT 50 MPH 120H 02/1800Z 31.0N 80.0W 45 KT 50 MPH $$ Forecaster Brennan |
