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Tropical Storm Marco Forecast Discussion Number 12
2020-08-23 10:58:57| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sun Aug 23 2020 000 WTNT44 KNHC 230858 TCDAT4 Tropical Storm Marco Discussion Number 12 NWS National Hurricane Center Miami FL AL142020 400 AM CDT Sun Aug 23 2020 Thunderstorm bursts continue to fire near the center of Marco, then weaken an hour or two later due to persistent shear. Overall, the storm's appearance hasn't changed with nearly all of the deep convection very near or northeast of the center. Although the satellite presentation is somewhat lacking at the moment, the earlier Air Force Reserve Hurricane Hunter mission found believable SFMR values to 60 kt, so that value remains the initial wind speed. The intensity forecast remains tricky with Marco due to its small size and marginal environment. There are some models that briefly relax the shear today, which will likely be enough of a change to allow Marco to reach hurricane strength. Later on, while the cyclone is near the coast of Louisiana, the shear is forecast to increase, but it is unknown exactly how close to landfall this will occur. Our best forecast at this time is that the strongest winds will be confined to the coast, and that Marco will then weaken faster than most hurricanes do over the swamps of Louisiana due to the shear. No significant changes were made to the intensity forecast, which is very close to the model consensus. The new forecast necessitates the issuance of hurricane warnings for portions of southeastern Louisiana. Marco continues moving north-northwestward or 335/11 kt. This general track and speed is likely today, with a turn to the northwest and decrease in forward speed expected as the storm weakens late Monday. While the track forecast is essentially unchanged from the previous one, there is still a fair bit of spread in the model guidance, likely tied to the intensity forecast. The stronger guidance is near or northeast of the new model consensus, due to the upper-level flow, and the NHC forecast leans in that direction, close to the previous official prediction. Key Messages: 1. Hurricane conditions, life-threatening storm surge, and heavy rainfall are expected from Marco along portions of the Gulf Coast beginning on Monday, and Hurricane and Storm Surge Warnings have been issued. Interests in these areas should follow any advice given by local government officials. 2. Tropical Storm Laura could bring additional storm surge, rainfall, and wind impacts to portions of the U.S. Gulf Coast by the middle of next week. This could result in a prolonged period of hazardous weather for areas that may also be affected by Marco. Interests there should monitor the progress of Marco and Laura and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 23.7N 87.0W 60 KT 70 MPH 12H 23/1800Z 25.3N 87.6W 65 KT 75 MPH 24H 24/0600Z 27.3N 88.6W 65 KT 75 MPH 36H 24/1800Z 29.0N 89.7W 65 KT 75 MPH 48H 25/0600Z 29.9N 91.5W 45 KT 50 MPH...INLAND 60H 25/1800Z 30.5N 93.1W 30 KT 35 MPH...INLAND 72H 26/0600Z 31.0N 95.0W 25 KT 30 MPH...INLAND 96H 27/0600Z...DISSIPATED $$ Forecaster Blake
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