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Tropical Storm Marco Forecast Discussion Number 9
2020-08-22 16:54:43| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sat Aug 22 2020 000 WTNT44 KNHC 221454 TCDAT4 Tropical Storm Marco Discussion Number 9 NWS National Hurricane Center Miami FL AL142020 1000 AM CDT Sat Aug 22 2020 Reconnaissance data, geostationary and microwave satellite imagery, and radar data from Cuba all indicate that Marco is strengthening quickly this morning. The Air Force Reserve Hurricane Hunters measured a peak 850-mb flight-level wind of 69 kt, and there were several SFMR measurements of 50-55 kt to the northeast of the center. These data support raising Marco's initial intensity to 55 kt, and the central pressure based on dropsonde data has fallen to 992 mb. The crew on the plane reported the formation of a partial eyewall, which agrees with what we've seen on recent microwave and radar images. The track forecast has been complicated by the fact that the plane has fixed Marco's center to the east of the previous forecast track, and that makes the current motion north-northwestward, or 340/10 kt. The subtropical ridge currently located over the southwestern Atlantic is forecast to build westward along the northern Gulf Coast during the next few days, and this expanding ridge is expected to push Marco northwestward and then eventually westward while the cyclone moves across the Gulf of Mexico. This general thinking has not changed, but the adjusted initial position ended up shifting the track guidance to the north and east on this cycle. In response, the new NHC track forecast has been adjusted eastward and northward during the first 3 days and is generally between the HCCA and TVCN consensus aids. Marco has finally tapped into the favorable conditions over the northwestern Caribbean Sea, and the cyclone's overall small size and small radius of maximum winds makes it susceptible to quick changes in intensity. The tropical storm is just beginning to move into a higher zone of shear to its north, but conditions should remain conducive enough for Marco to intensity to a hurricane during the next 24 hours. After that time, southwesterly shear is expected to increase over 20 kt by day 2 and then over 30 kt by day 3, and those conditions, along with the cyclone's small size, should cause weakening as Marco gets closer to the central and northwestern Gulf coast. The updated NHC intensity forecast has been increased during the first 2 days and lies above the HCCA/Florida State Superensemble solutions but below the SHIPS/LGEM scenarios. The intensity forecast comes back in line with the previous forecast by day 3 during the expected weakening phase, and Marco is ultimately expected to dissipate over Texas by the end of the forecast period. The updated track forecast suggests that watches could be required for a portion of the central Gulf Coast later today. Key Messages: 1. Marco is forecast to strengthen to a hurricane as it moves into the southeastern Gulf of Mexico by tonight, and tropical storm conditions are expected over the northeastern coast of the Yucatan Peninsula and in extreme western Cuba. Heavy rainfall is also expected in the eastern portions of the Mexican states of Quintana Roo and Yucatan, and across far western Cuba, which could result in flash flooding. 2. Marco is expected to move across the central Gulf of Mexico as a hurricane Sunday and approach the central Gulf Coast on Monday. There is an increasing risk of impacts from storm surge, winds, and heavy rainfall from the upper Texas coast to Louisiana early next week, and interests there should monitor the progress of Marco, as storm surge, tropical storm, and/or hurricane watches could be issued later today. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 20.9N 85.3W 55 KT 65 MPH 12H 23/0000Z 22.1N 86.0W 65 KT 75 MPH 24H 23/1200Z 23.9N 87.1W 75 KT 85 MPH 36H 24/0000Z 25.6N 88.4W 75 KT 85 MPH 48H 24/1200Z 27.2N 89.9W 70 KT 80 MPH 60H 25/0000Z 28.5N 91.6W 60 KT 70 MPH 72H 25/1200Z 29.1N 93.6W 50 KT 60 MPH 96H 26/1200Z 29.3N 96.6W 35 KT 40 MPH...INLAND 120H 27/1200Z...DISSIPATED $$ Forecaster Berg
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