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| #797423 (Received by flhurricane at: 4:44 PM 22.Aug.2015) TCDAT4 HURRICANE DANNY DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015 500 PM AST SAT AUG 22 2015 Satellite imagery and reports from Air Force Reserve and NOAA Hurricane Hunter aircraft show that Danny continues to weaken. The aircraft have reported that the central pressure has risen to at least 991 mb, along with maximum surface wind estimates near 65 kt from the Stepped Frequency Microwave Radiometer. Based on these data, the initial intensity is decreased to 65 kt. The aircraft data indicate that the center of Danny is tilted to the north or northeast with height, as dropsondes released at the calm flight-level center have consistently reported 50-60 kt easterly surface winds. In addition, satellite imagery suggests that the center is now at the southwestern edge of the convection. These observations are likely due to ongoing southwesterly vertical wind shear. The initial motion is now 285/12, a little faster than before. There is again little change in the forecast philosophy, with Danny expected to turn westward tonight as the subtropical ridge to the north of the cyclone builds westward and strengthens. This general motion is expected to persist for the next several days taking Danny across the Leeward Islands in about two days, and near Puerto Rico and Hispaniola in 3 to 4 days. This part of the forecast track is near the center of the guidance envelope and is similar to, but a little faster than, the previous track. The dynamical models are forecasting a mid- to upper-level trough to move into Florida and the southeastern United States by 120 hours, and the track guidance responds to this by showing a northwestward turn. The new forecast track also shows a more northward motion at 120 hours, but it lies to the south and west of the center of the envelope. Danny is expected to move through a dry and stable air mass and encounter moderate to strong southwesterly vertical wind shear for at least the next three days. This should cause continued weakening, and the cyclone is forecast to be a tropical storm as it moves over or near the northeastern Caribbean Islands. The intensity forecast becomes lower confidence at days 4 and 5. The dynamical models forecast an upper-level low to form near central Cuba. However, they do not agree on how this will change the shear over Danny. The GFS continues forecasting significant shear, while the ECMWF forecasts more favorable upper-level winds. It should be noted that even with its more favorable shear forecast, the ECMWF forecasts Danny to weaken to a tropical wave. Based on this and the expectation that dry air will continue to impact the cyclone, the intensity forecast calls for continued weakening at days 4-5. There are no changes to the watches at this time. However, additional watches or warnings may be necessary for portions of the Leeward Islands, the Virgin Islands, and Puerto Rico tonight or Sunday. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 15.8N 53.3W 65 KT 75 MPH 12H 23/0600Z 16.1N 55.2W 60 KT 70 MPH 24H 23/1800Z 16.6N 57.9W 55 KT 65 MPH 36H 24/0600Z 17.1N 60.4W 50 KT 60 MPH 48H 24/1800Z 17.8N 62.9W 45 KT 50 MPH 72H 25/1800Z 19.5N 68.0W 40 KT 45 MPH 96H 26/1800Z 21.0N 72.5W 35 KT 40 MPH 120H 27/1800Z 23.0N 76.0W 30 KT 35 MPH $$ Forecaster Beven |
