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Tropical Storm Marco Forecast Discussion Number 8
2020-08-22 10:50:42| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sat Aug 22 2020 000 WTNT44 KNHC 220850 TCDAT4 Tropical Storm Marco Discussion Number 8 NWS National Hurricane Center Miami FL AL142020 400 AM CDT Sat Aug 22 2020 SFMR data from the last leg of the 53rd Air Force Reserve reconnaissance aircraft indicated a couple of 48-50 kt winds, but were associated with a significant spike in the rainfall rate. Additionally, the flight-level winds were only 36 kt in that area and the central pressure has increased a little to 1005 mb. The cloud pattern has improved during the past several hours with deep convection developing near the center and spiral bands forming over the eastern portion of cyclone. Based on a blend the hurricane hunter data and current subjective satellite intensity estimates, the initial intensity is raised to 40 kt. Although the UW-CIMSS shear product and global models indicate a favorable upper wind pattern, GOES-16 sounder analysis data show a higher than normal vertically stable environment in the western Caribbean. This negative contribution maybe what's hampering significant development. Consequently, as shown in the previous advisory, only modest strengthening is indicated in the NHC forecast through 48 hours. Only the Decay SHIPS and LGEM intensity models indicate that Marco will become a hurricane in a couple of days. Both the HMON and HWRF have backed off of showing a hurricane in the Gulf. Afterward, increasing west-southwesterly shear should lead to weakening as the cyclone turns toward the northwestern Gulf coast. The NHC forecast lies between the higher LGEM/Decay SHIPS solution and the lower NOAA HCCA intensity model which indicates a peak intensity of 55 kt. The initial motion is estimated to be west-northwestward, or 335/10 kt. Marco is being steered toward the northwest by a mid- to upper-level cut-off low and associated trough extending into the southwestern Gulf from the Mississippi Valley. By Sunday, the aforementioned feature is forecast to lift northeastward allowing the subtropical ridge to build back over the central gulf. This should cause Marco to turn northwestward and west-northwestward early next week toward the the northwestern Gulf coast. Large-scale guidance generally agree that any binary direct or indirect interaction, while both systems are in the gulf and at near equal latitude, is unlikely at this point. The official track forecast has been adjusted to the right of the previous advisory and lies just to the left of the various multi-model consensus aids. The 34 kt wind radii have been adjusted based on the aircraft reconnaissance data and a 0224 UTC scatterometer pass. Key Messages: 1. Marco is forecast to strengthen over the northwestern Caribbean Sea through Saturday as it approaches the northeast coast of the Yucatan Peninsula. A Hurricane Watch and a Tropical Storm Warning are in effect for portions of that region. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Although some strengthening is anticipated on Sunday, weakening is forecast as the system approaches the northwestern Gulf coast on Tuesday. It is still too soon to know exactly the location and magnitude of impacts the system will produce along the central or northwestern Gulf Coast, and interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 19.6N 85.4W 40 KT 45 MPH 12H 22/1800Z 20.9N 86.1W 45 KT 50 MPH 24H 23/0600Z 22.5N 87.1W 50 KT 60 MPH 36H 23/1800Z 24.1N 88.3W 55 KT 65 MPH 48H 24/0600Z 25.7N 89.9W 60 KT 70 MPH 60H 24/1800Z 27.3N 91.3W 55 KT 65 MPH 72H 25/0600Z 28.3N 93.4W 50 KT 60 MPH 96H 26/0600Z 29.1N 96.2W 40 KT 45 MPH...INLAND 120H 27/0600Z 29.6N 97.8W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts
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