000 WTNT43 KNHC 162031 TCDAT3 HURRICANE GONZALO DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082014 500 PM AST THU OCT 16 2014 Recent microwave data indicate that Gonzalo has a concentric eyewall structure, with a small open inner ring of convection surrounded by a larger closed ring. The satellite presentation has not changed appreciably since this morning, and the CI estimate from the UW-CIMSS ADT supports maintaining the initial intensity at 125 kt. An Air Force reconnaissance aircraft is scheduled to investigate Gonzalo later this evening and should give us a better handle on the hurricane's current intensity. Light westerly shear has been affecting Gonzalo, but it hasn't been enough to disrupt the hurricane's structure. Vertical shear is forecast to increase slightly during the next 12-24 hours, and then increase substantially after 48 hours. Also, sea surface temperatures along Gonzalo's forecast path are expected to be at least 26C for the next 48 hours. Therefore, only gradual weakening is anticipated during the next couple of days while Gonzalo moves near Bermuda. More rapid weakening should occur after 48 hours once Gonzalo moves north of the Gulf Stream and is affected by 40-50 kt of westerly shear. The NHC intensity forecast closely follows the intensity consensus ICON, and no significant changes were required to the previous forecast. The global models indicate that Gonzalo will likely become extratropical by 72 hours, and that is now indicated in the NHC forecast. Gonzalo has turned north-northeastward and begun to accelerate with an initial motion estimate of 015/8 kt. The hurricane is entering the flow ahead of a deep-layer trough located over the eastern United States, and this pattern is expected to cause Gonzalo to accelerate further toward the north-northeast during the next 48 hours. After 48 hours, the cyclone is forecast to turn northeastward and east-northeastward over the north Atlantic. The track guidance is tightly clustered for much of the forecast period. However, the new models are again a little slower than the previous forecast, and they have shifted northwestward between 48-72 hours. The updated NHC track forecast has also been shifted northwestward during that time toward the TVCA model consensus. Significant coastal flooding on Bermuda is likely if Gonzalo continues on the current NHC forecast track. Although specific amounts cannot be forecast for Gonzalo, Hurricane Fabian produced an estimated 10 feet of storm surge when it moved over Bermuda as a major hurricane in 2003, and similar values could occur with Gonzalo. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 27.1N 68.2W 125 KT 145 MPH 12H 17/0600Z 28.7N 67.3W 120 KT 140 MPH 24H 17/1800Z 31.1N 65.9W 110 KT 125 MPH 36H 18/0600Z 34.3N 64.0W 100 KT 115 MPH 48H 18/1800Z 39.0N 60.8W 95 KT 110 MPH 72H 19/1800Z 50.5N 46.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 20/1800Z 55.0N 21.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 21/1800Z...DISSIPATED $$ Forecaster Berg