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| #1013690 (Received by flhurricane at: 4:50 PM 24.Aug.2020) TCDAT4 Tropical Storm Marco Discussion Number 19 NWS National Hurricane Center Miami FL AL142020 400 PM CDT Mon Aug 24 2020 There has been little change to the structure of Marco over the past few hours, with the deep convection and associated heavy rainfall being sheared well to the northeast of the exposed center of circulation. Based on earlier Hurricane Hunter aircraft and scatterometer data, there was a small area of tropical-storm-force winds in the strongest convection located about 50-75 n mi offshore of the northern Gulf coast. Since the shower and thunderstorm activity is persisting, it is assumed that these winds are still occurring in that offshore area and the initial intensity is being held at 35 kt. The exposed vortex should continue to spin down as the center of the cyclone reaches the southeastern Louisiana coast late this evening, which would result in the coastal areas being spared from experiencing sustained tropical-storm-force winds. The official NHC forecast shows Marco weakening to a tropical depression tonight, which is in agreement with the model guidance. Strong vertical wind shear should strip away any remaining convection associated with Marco at some point tonight, as indicated by GFS and ECMWF simulated satellite imagery. When the convection does diminish, most of the model guidance does not show any significant new convection developing thereafter. So it is anticipated that Marco will degenerate to a remnant low by Tuesday. Marco's initial motion is northwest at 6 kt. As the cyclone continues to weaken and degenerate to a remnant low, a turn to the west-northwest is expected as the system becomes steered in the low-level flow. The latest NHC track forecast is little changed from the previous one, and is near the TVCN consensus track guidance. Key Messages: 1. Gusty winds, heavy rainfall, and lingering coastal flooding are expected from Marco along portions of the Gulf Coast through this evening. For information on these hazards see products from your local National Weather Service office. 2. Tropical Storm Laura could bring dangerous storm surge, rainfall, and wind impacts to portions of the U.S. Gulf Coast by the middle of the week, and tropical cyclone wind and surge watches have been issued for portions of the U.S. Gulf Coast. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 29.0N 88.9W 35 KT 40 MPH 12H 25/0600Z 29.7N 89.9W 30 KT 35 MPH...INLAND 24H 25/1800Z 30.3N 91.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 26/0600Z 30.8N 94.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 26/1800Z...DISSIPATED $$ Forecaster Latto |