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| #1013507 (Received by flhurricane at: 4:56 PM 23.Aug.2020) TCDAT4 Hurricane Marco Discussion Number 14 NWS National Hurricane Center Miami FL AL142020 400 PM CDT Sun Aug 23 2020 Shortly after the 10 AM CDT advisory was issued, the Air Force Reserve Hurricane Hunter aircraft investigating Marco measured SFMR winds of 65 to 69 kt for several minutes. A dropsonde around the same time also measured winds equivalent to 64 kt at the surface. Based on these data, it was evident that Marco had strengthened into a hurricane. Since that time, the convective pattern has changed little, and the final leg of the aircraft mission did not reveal any notable changes to the cyclone's intensity. Therefore, the initial intensity has been set to 65 kt, which is also in agreement with the latest Dvorak intensity estimate from SAB. Marco continues to move north-northwest at around 11 kt. Model guidance is in good agreement on a north-northwest and then northwest motion into Monday morning as Marco nears the northern Gulf coast. However, there has been a major shift in the track guidance beyond Monday morning, and the majority of the forecast models now keep Marco offshore of the northern Gulf coast for the next few days rather than moving it inland over Louisiana Monday afternoon. Since this shift was so abrupt, I would rather split the difference between the previous official forecast track and the latest consensus tracks until another round of model runs can confirm this new suggested track is higher confidence. Based on this shift in track, tropical storm conditions are expected farther west along the Louisiana coast, and a Tropical Storm Warning has been issued from Morgan City to Cameron, Louisiana. It should be noted that if the trend in the models are correct, some of the impacts over portions of the north-central Gulf coast could be lessened. The current shear analysis from UW-CIMSS shows that Marco is experiencing about 20-25 kt of southwesterly shear, yet Marco has been able to slowly strengthen in this environment today, likely due to the presence of very warm waters and plenty of atmospheric moisture. By late tonight and through Monday, the SHIPS guidance suggests this shear will increase to over 30 kt. This should limit any further intensification, and could cause Marco to weaken before it nears the northern Gulf coast Monday afternoon. By Monday night, the shear is forecast to increase to close to 40 kt, which should strip the convection away from the center of the cyclone, causing it to weaken. After 48 h, Marco is now expected to become a remnant low devoid of deep convection. The official NHC intensity forecast is similar to the previous one, but is at the high end of the guidance through 24 h. 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. 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 the 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 23/2100Z 25.8N 87.8W 65 KT 75 MPH 12H 24/0600Z 27.1N 88.6W 65 KT 75 MPH 24H 24/1800Z 28.5N 89.7W 65 KT 75 MPH 36H 25/0600Z 29.3N 91.4W 50 KT 60 MPH...INLAND 48H 25/1800Z 29.8N 93.2W 35 KT 40 MPH...INLAND 60H 26/0600Z 29.9N 95.1W 30 KT 35 MPH...POST-TROP/INLAND 72H 26/1800Z 29.7N 96.8W 25 KT 30 MPH...POST-TROP/INLAND 96H 27/1800Z...DISSIPATED $$ Forecaster Latto |
