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Hurricane Lorenzo Forecast Discussion Number 31
2019-09-30 04:42:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 29 2019 000 WTNT43 KNHC 300242 TCDAT3 Hurricane Lorenzo Discussion Number 31 NWS National Hurricane Center Miami FL AL132019 1100 PM AST Sun Sep 29 2019 There haven't been a lot of changes with Lorenzo this evening, with a small cloud-filled eye remaining visible and an enormous cloud shield expanding in the northern semicircle. Satellite intensity estimates support a somewhat lower intensity than the previous advisory, so the initial wind speed is set to 95 kt. It should be emphasized that even though the peak winds are down since yesterday, the area of the hurricane-force winds has more than doubled during that time. Earlier aircraft data indicated that the large hurricane is upwelling a significant amount of cooler waters under the storm, and this is anticipated to cause Lorenzo to slowly weaken during the next couple of days. While the SSTs drop off considerably after late tomorrow, which would normally cause faster weakening, most of the guidance is showing a favorable trough interaction at that time with strong upper-level divergence. These effects are expected to offset, and Lorenzo is likely to be a category 1 or 2 hurricane near the Azores. Little change was made to the previous forecast, except to raise the intensity a little higher near the Azores after more heavily weighting the global models, which have been good performers for this cyclone. The guidance is in very good agreement on Lorenzo becoming an extratropical cyclone in about 72 hours, and that is reflected in the latest forecast. Lorenzo continues north-northeastward at 9 kt through a break in the subtropical ridge. The forecast track confidence remains very high through 48 hours as the hurricane is accelerated toward the northeast ahead of a mid-latitude trough, and the new forecast is essentially an update of the previous one. After that time, however, there is a very large spread in the guidance caused by whether Lorenzo is captured by the mid-latitude trough or if it remains separate. There isn't much change in the newest guidance, although it should be noted that the 12Z ECMWF solution is pretty far east of its ensemble mean. The forecast track confidence is extremely low beyond 72 hours, and the new NHC track was nudged just a little to the left from the previous advisory, slightly east of the various consensus aids. Key Messages: 1. Lorenzo is a large and powerful hurricane, and its hurricane- and tropical-storm-force wind fields are expected to expand further during the next several days. Hurricane and Tropical Storm Watches have been issued for the Azores, and these winds could start late Tuesday or early Wednesday. 2. Large swells generated by Lorenzo will continue to spread across much of the north Atlantic basin during the next few days. These swells will produce life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 27.6N 43.5W 95 KT 110 MPH 12H 30/1200Z 28.9N 42.9W 90 KT 105 MPH 24H 01/0000Z 31.0N 41.5W 90 KT 105 MPH 36H 01/1200Z 33.9N 38.6W 85 KT 100 MPH 48H 02/0000Z 37.5N 34.2W 85 KT 100 MPH 72H 03/0000Z 48.0N 22.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 96H 04/0000Z 53.0N 17.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 05/0000Z 54.0N 17.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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