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| #796840 (Received by flhurricane at: 11:03 AM 20.Aug.2015) TCDAT4 HURRICANE DANNY DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015 1100 AM AST THU AUG 20 2015 Danny's cloud pattern has continued to improve since the previous advisory, and a 10 n mi diameter eye has become embedded in the center of a small central dense overcast. Water vapor imagery indicates that upper-level outflow has become more symmetrical. The initial intensity of 65 kt is based on NHC objective Dvorak classifications of T4.1-T4.2 using an eye feature. Conventional and microwave satellite images indicate that Danny is an unusually small tropical cyclone. Satellite fixes indicate that Danny is now moving west-northwestward or 295/10 kt. The latest model guidance remains in very good agreement on Danny moving west-northwestward for the next 48-72 hours toward a weakness in the subtropical ridge along 60W longitude. A mid- to upper-level trough north of Bermuda is forecast by the global models to begin lifting out to the north in 96-120 hours, which should allow the subtropical ridge to the north of Danny to build back westward, forcing Danny on a more westward track on days 4 and 5. The NHC official forecast track is essentially an update of the previous advisory through 72 hours, but was shifted a little north of the previous track after that in agreement with the consensus model TVCN. Danny's compact size makes it subject to significant fluctuations in strength, both up and down, and such fluctuations are notoriously difficult to forecast. Low-shear conditions are expected to continue for the next 36 hours or so, which argues for some further strengthening during that time. However, the cyclone continues to be surrounded by dry mid-level air, which could penetrate into the core and disrupt the intensification process. By 48 hours and beyond, the vertical wind shear is forecast to become southerly to southwesterly and increase to near 15 kt. As a result, Danny is expected to be weakening as it approaches the Leeward Island. The official intensity forecast calls for a peak intensity somewhat higher and earlier than the previous advisory, ending up close to the IVCN consensus model. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 12.5N 44.8W 65 KT 75 MPH 12H 21/0000Z 13.1N 46.0W 70 KT 80 MPH 24H 21/1200Z 14.0N 47.6W 75 KT 85 MPH 36H 22/0000Z 14.7N 49.4W 75 KT 85 MPH 48H 22/1200Z 15.2N 51.5W 70 KT 80 MPH 72H 23/1200Z 16.0N 56.4W 65 KT 75 MPH 96H 24/1200Z 16.9N 61.7W 65 KT 75 MPH 120H 25/1200Z 18.0N 66.6W 55 KT 65 MPH $$ Forecaster Stewart |
