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| #699898 (Received by flhurricane at: 5:00 PM 04.Jul.2014) TCDAT1 HURRICANE ARTHUR DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012014 500 PM EDT FRI JUL 04 2014 The cloud pattern of Arthur remains very symmetric with a hint of an eye remaining in visibile and infrared satellite imagery, although the cloud tops have continued to gradually warm during the day. Recent reconnaissance data show that the radius of maximum winds has increased, which is likely the first sign that the hurricane is beginning the transition to a post-tropical cyclone. The aircraft data also indicate that the winds aloft are not mixing down as efficiently as they were overnight and this morning. In fact, during the latest pass through the southeastern quadrant the aircraft measured a peak 700-mb flight level wind of 103 kt, but the surface winds underneath were only 63 kt. Based on these data, the initial intensity is lowered to 70 kt. Arthur is now located over sea surface temperatures of around 24C. The hurricane will be moving over progressively colder waters and into an area of increasing southwesterly shear, which should result in continued weakening. Global model guidance indicates that Arthur should become post-tropical tomorrow morning. After the extratropical transition, the cyclone is forecast to continue weakening as it moves over the North Atlantic. The initial motion estimate is 040/23 kt. The hurricane should continue to move northeastward during the next 24 to 36 hours in deep-layer southwesterly flow ahead of the approaching deep-layer trough. After that time, the post-tropical cyclone is forecast to slow down and eventually turn east-northeastward. There is still a large amount of spread in the track guidance after 48 hours. The updated NHC forecast is between the ECWMF and GFS models, and leans toward guidance provided by the NOAA Ocean Prediction Center. Winds in excess of gale/tropical storm force are expected over portions of eastern Maine on Saturday. Because Arthur is expected to be extratropical by Saturday morning, and because the strong winds in Maine will be post-frontal, this threat is being handled by high wind warnings issued by local NWS offices. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 39.4N 71.1W 70 KT 80 MPH 12H 05/0600Z 42.2N 68.2W 60 KT 70 MPH 24H 05/1800Z 45.3N 65.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 36H 06/0600Z 47.0N 61.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 06/1800Z 49.4N 57.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 07/1800Z 56.0N 51.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 08/1800Z 60.0N 49.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 09/1800Z 61.0N 42.5W 25 KT 30 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown |
