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Tropical Storm Arthur Forecast Discussion Number 5
2020-05-17 22:32:15| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Sun May 17 2020 000 WTNT41 KNHC 172032 TCDAT1 Tropical Storm Arthur Discussion Number 5 NWS National Hurricane Center Miami FL AL012020 500 PM EDT Sun May 17 2020 Arthur's satellite presentation has not changed much since the previous advisory. There are still some fragmented convective bands over the eastern portions of the circulation, but convective activity remains limited over the western half of the storm. A late-arriving ASCAT overpass from around the time of the previous advisory revealed somewhat lower wind speeds than reported by this morning's reconnaissance aircraft. This could be the result of the convection becoming more fragmented after the aircraft sampled that portion of the storm or related to the low bias of the ASCAT instrument. Regardless, the initial intensity remains a possibly generous 40 kt for now. Another reconnaissance aircraft is scheduled to investigate Arthur this evening. Arthur is forecast to remain within a low wind shear environment and over marginally warm sea surface temperatures through early Monday. These conditions favor some strengthening, however the sprawling structure of the cyclone and nearby dry mid-level air are likely to temper any increase in wind speed. After 36-48 hours, baroclinic forcing is expected to help the post-tropical cyclone maintain its intensity. Later in the period, the frontal gradients decrease which should cause weakening. Recent satellite fixes show that the Arthur is still moving north-northeastward at about 8 kt. The tropical storm should begin to accelerate northeastward overnight as a mid-level trough moves into the eastern United States. By Tuesday night, the steering flow is expected to become westerly which should cause Arthur to turn eastward, then southeastward later in the forecast period. The lastest dynamical track guidance has come into a little better agreement through 36-48 hours with the GFS and ECMWF converging on the previous NHC track. As a result, little change was needed to the first couple of days of the earlier NHC track forecast. After that time, most of the guidance has trended toward a faster eastward and east-southeastward motion, and the NHC forecast has been adjusted accordingly in that direction as well. Key Messages: 1. A Tropical Storm Warning is in effect for a portion of the North Carolina coast. Tropical-storm-force winds and heavy rains are expected there on Monday. 2. Dangerous coastal surf conditions and rip currents are expected to spread northward along the southeast U.S. coast to the mid-Atlantic states during the next couple of days. See products from your local National Weather Service Forecast Office for more details. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 31.5N 77.2W 40 KT 45 MPH 12H 18/0600Z 33.1N 76.4W 40 KT 45 MPH 24H 18/1800Z 35.3N 74.6W 45 KT 50 MPH 36H 19/0600Z 36.6N 71.9W 50 KT 60 MPH 48H 19/1800Z 36.8N 69.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 20/0600Z 36.3N 67.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 20/1800Z 35.6N 66.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 21/1800Z 34.0N 64.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 22/1800Z...DISSIPATED $$ Forecaster Brown
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