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| #804136 (Received by flhurricane at: 11:01 AM 30.Sep.2015) TCDAT1 HURRICANE JOAQUIN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 1100 AM EDT WED SEP 30 2015 Joaquin has continued to strengthen overnight. Satellite imagery shows that the convection has become more symmetric, and recent visible images show what might be an eye trying to form. An Air Force Reserve Hurricane Hunter aircraft reported 700-mb flight- level winds of 83 kt and estimated 70 kt surface winds from the Stepped Frequency Microwave Radiometer, with a central pressure of 971 mb estimated from the aircraft data. Based on these, the initial intensity is increased to 70 kt. Joaquin has moved a little south of the previous track with an initial motion of 230/5. The shortwave ridge causing this motion is expected to weaken during the next 24-48 hours as a strong deep-layer trough develops over the southeastern United States. This is expected to cause the hurricane to turn northward by 72 hours. There is disagreement in the track guidance between the ECMWF and the other dynamical models. The majority of the guidance forecasts Joaquin to turn west of north after 48-72 hours, with the storm moving inland over the mid-Atlantic states and merging with the trough. On the other hand, the ECMWF forecast the hurricane to move out to sea between North America and Bermuda. The ECMWF forecasts Joaquin to move more to the south during the first 24-48 hours than the other models. In addition, it shows the hurricane interacting with an upper-level low to its northeast that results in a more eastward motion after 48 hours. The new forecast track, which is similar to the previous track, leans more toward the non-ECMWF guidance. However, out of deference to the ECMWF, it lies to the east of the center of the guidance envelope and the consensus models. The NOAA G-IV jet is scheduled to fly a synoptic surveillance mission this afternoon, which, along with special rawinsonde launches over the eastern U. S., hopefully will reduce the spread of the guidance. Joaquin is expected to remain in an environment of moderate northeasterly vertical shear for the next 24-36 hours. However, since it has been steadily strengthening in such an environment, there is no obvious reason to think it will stop doing so. After 36 hours, the hurricane is likely to move into an area of divergent southerly upper-level winds associated with the eastern U. S. trough. While there is uncertainty as to how much shear should occur, it is expected that additional intensification could occur through 72 hours. Based on this, the intensity forecast calls for Joaquin to peak as a major hurricane in about 72 hours, and it is possible it could be stronger than currently forecast. After 72 hours, increasing shear and cold air intrusion should cause weakening and the start of extratropical transition. KEY MESSAGES: 1. Confidence in the details of the track forecast late in the period remains low, since the environmental steering currents are complex and the model guidance is inconsistent. A wide range of outcomes is possible, from a direct impact of a major hurricane along the U.S. east coast to a track of Joaquin out to sea away from the coast. It is therefore way too soon to talk about specific wind, rain, or surge impacts from Joaquin in the U.S. 2. Should the threat to the U.S. increase, any further adjustments of the forecast to the west would likely be accompanied by an increase in the forecast forward speed, with impacts along the coast occurring sooner than currently forecast. A hurricane watch could be required for portions of the U.S. coast as early as Thursday evening. 3. Many areas of the eastern U.S. are currently experiencing heavy rains and gusty winds associated with a frontal system. This inclement weather is expected to continue over the next few days, which could complicate preparations for Joaquin should it head toward the coast. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 24.7N 72.6W 70 KT 80 MPH 12H 01/0000Z 24.3N 73.2W 80 KT 90 MPH 24H 01/1200Z 24.1N 74.0W 85 KT 100 MPH 36H 02/0000Z 24.4N 74.4W 90 KT 105 MPH 48H 02/1200Z 25.3N 74.5W 95 KT 110 MPH 72H 03/1200Z 28.5N 73.5W 100 KT 115 MPH 96H 04/1200Z 34.0N 73.0W 90 KT 105 MPH 120H 05/1200Z 38.5N 74.0W 75 KT 85 MPH $$ Forecaster Beven |
