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Hurricane JOAQUIN Forecast Discussion Number 12
2015-09-30 22:55:49| National Hurricane Center (Atlantic)
Issued at 500 PM EDT WED SEP 30 2015 000 WTNT41 KNHC 302055 TCDAT1 HURRICANE JOAQUIN DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 500 PM EDT WED SEP 30 2015 There has been little change in the organization of Joaquin during the past several hours. While the hurricane continues to produce cloud tops colder than -80C in the eyewall, the eye has not become better defined since the last advisory. Satellite intensity estimates are 77 kt from both TAFB and SAB, so the advisory intensity is now 75 kt. The initial motion is 225/7. 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. Thus, a generally southwestward motion is expected for the next 36 hours or so, followed by a turn toward the north as the trough becomes the dominant steering mechanism. There is an increased disagreement between the GFS, UKMET, Canadian, and NAVGEM models versus the ECMWF since the last advisory. The ECMWF has continued its forecast of showing a northeastward motion after 72 hours, taking Joaquin just west of Bermuda and out to sea. The other models have all shifted their forecasts to the left and now call for landfall in the Carolinas and the mid-Atlantic states, followed by merger with the baroclinic trough. Given the shift in the non-ECMWF models, a major westward adjustment has been made to the forecast track at 96 and 120 hours, bringing the center of Joaquin near or over portions of the mid-Atlantic states. Due to the use of the ECMWF in the consensus models, the new track lies near the various consensus models. However, it lies well to the east of the GFS and the other similar models. The NOAA G-IV jet is currently flying a synoptic surveillance mission, which, along with special rawinsonde launches, hopefully will reduce the spread of the guidance. There is little change to the intensity forecast philosophy since the last advisory. Joaquin is expected to remain in an environment of moderate northeasterly vertical shear for the next 24-36 hours, possibly including strong winds seen at 400 mb in recent dropsondes from the G-IV aircraft. 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 at least 48 hours. Based on this, the intensity forecast calls for Joaquin to peak as a major hurricane in 48-72 hours, and it is possible it could be stronger than currently forecast. After 72 hours, increasing shear, cold air intrusion, and land interaction should cause weakening and the start of extratropical transition. KEY MESSAGES: 1. Preparations to protect life and property within the warning areas in the Bahamas should be rushed to completion. 2. A significant adjustment to the forecast has been made this afternoon, and this shows an increased threat to the mid-Atlantic states and the Carolinas. However, confidence in the details of the forecast after 72 hours remains low, since we have one normally excellent model that keeps Joaquin far away from the United States east coast. The range of possible outcomes is still large, and includes the possibility of a major hurricane landfall in the Carolinas. 3. Every effort is being made to provide the forecast models with as much data as possible. The NOAA G-IV jet has begun a series of missions in the storm environment, and the National Weather Service is launching extra balloon soundings. 4. Because landfall, if it occurs, is still more than three days away, it is too early to talk about specific wind, rain, or surge impacts from Joaquin in the United States. Even if Joaquin stays well out to sea, strong onshore winds will create minor to moderate coastal flooding along the coasts of the mid-Atlantic and northeastern states through the weekend. 5. A hurricane watch for a portion of the U.S. coast could be required as early as Thursday evening. 6. 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, and greatly exacerbate the impacts from the hurricane. Heavy rains are likely to continue over these areas even if the center of Joaquin stays out to sea. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 24.3N 73.1W 75 KT 85 MPH 12H 01/0600Z 24.0N 73.8W 85 KT 100 MPH 24H 01/1800Z 23.9N 74.5W 90 KT 105 MPH 36H 02/0600Z 24.5N 75.0W 95 KT 110 MPH 48H 02/1800Z 25.8N 75.0W 100 KT 115 MPH 72H 03/1800Z 30.5N 74.5W 100 KT 115 MPH 96H 04/1800Z 36.0N 75.5W 85 KT 100 MPH 120H 05/1800Z 38.5N 76.5W 55 KT 65 MPH $$ Forecaster Beven
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