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| #1153555 (Received by flhurricane at: 4:44 PM 19.Sep.2023) TCDAT5 Hurricane Nigel Discussion Number 18 NWS National Hurricane Center Miami FL AL152023 500 PM AST Tue Sep 19 2023 The satellite structure of Nigel has improved this afternoon. Satellite images indicate a solid ring of deep convection surrounds the large, 45 to 50-n-mi wide eye of the hurricane. The NOAA Hurricane Hunters have conducted research missions into Nigel today and provided helpful data to better assess the hurricane`s structure and intensity. The aircraft recorded peak 700-mb flight-level winds of around 100 kt, which reduces to a surface intensity of 90 kt using a standard reduction factor. However, peak SFMR winds from both planes were around 75 kt, and dropsonde data indicate only modest pressure falls to around 974 mb. Based on a blend of these data, the initial intensity is set at 85 kt for this advisory. The wind radii were adjusted slightly outward based on the aircraft data and scatterometer data received just after the previous advisory. Given its improved structure, additional near-term strengthening is forecast as Nigel moves over 28C SSTs in a weak vertical shear environment. By late Wednesday, the guidance indicates deep-layer shear will increase while the hurricane quickly moves into a drier environment over much cooler waters. So, the NHC forecast shows steady weakening through late week that closely follows the latest multi-model consensus aids. The global model fields indicate that Nigel will complete its extratropical transition by 60 h, which is reflected in this advisory. It appears that Nigel has begun to turn more northward, and its initial motion is now north-northwestward (330/12 kt). The steering ridge to the northeast of Nigel will continue to slide eastward through tonight. As a result, the hurricane is expected to turn northward around the western periphery of this ridge. Then, Nigel should turn northeastward and accelerate within the flow ahead of a deep-layer trough moving across the northeastern United States and Atlantic Canada. The track guidance remains well clustered around this scenario, and the latest NHC track forecast was only nudged slightly west based on the latest TVCA and HCCA aids. As Nigel moves deeper into the mid-latitudes, the extratropical low is forecast to become captured within a broader cyclonic circulation over the north Atlantic on days 4 and 5, which introduces increased track uncertainty late in the period. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 31.8N 54.7W 85 KT 100 MPH 12H 20/0600Z 33.7N 54.9W 95 KT 110 MPH 24H 20/1800Z 36.7N 53.3W 90 KT 105 MPH 36H 21/0600Z 39.8N 49.3W 80 KT 90 MPH 48H 21/1800Z 42.8N 42.9W 70 KT 80 MPH 60H 22/0600Z 45.7N 35.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 22/1800Z 48.6N 28.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 23/1800Z 56.0N 20.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 24/1800Z 58.0N 21.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Reinhart |
