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Tropical Storm Theta Forecast Discussion Number 14
2020-11-13 09:38:31| National Hurricane Center (Atlantic)
Issued at 900 AM GMT Fri Nov 13 2020 000 WTNT45 KNHC 130838 TCDAT5 Tropical Storm Theta Discussion Number 14 NWS National Hurricane Center Miami FL AL302020 900 AM GMT Fri Nov 13 2020 A fortuitous 0348 UTC AMSR2 microwave pass revealed that Theta's surface center was a little to the north of the previous advisory position. The image also indicated that the coldest brightness temperatures were located in the northeast quadrant which sort of conflicts with the earlier scatterometer data showing the stronger surface winds in the southeast quadrant. More than likely though, these winds are being produced by the pressure gradient of the cyclone and a mid-level ridge to the southeast. Since the cloud pattern has changed little during the past several hours and the subjective satellite intensity estimate from TAFB hasn't either, the initial intensity is held at 50 kt for this advisory. Theta is forecast to change little in intensity during the next 12 hours or so as the cyclone continues moving in a low shear zone associated with a mid- to upper-level trough axis. On Saturday, the trough migrates south of Theta, while strong northerly shear and a more stable air mass intrude from the northwest to north. As a result, Theta is expected to spin down and degenerate to a remnant low on Sunday and dissipate by mid next week. Theta has been moving eastward during the last 12 hours within the mid-level troposphere steering current provided by a mid-level ridge extending westward from west Africa to the eastern tropical Atlantic. The short term motion, however, already appears to be the anticipated to the right of track motion, or toward the east-southeast. Regardless, this general motion along with a reduction in forward speed is forecast during the next couple of days as a more vertically shallow Theta is influenced by the low-level flow. By day 3, the remnants of Theta are expected to turn rather sharply northward and continue in this general motion in response to an approaching deep-layer mid-latitude cyclone from the northeastern Atlantic. The NHC forecast is similar to the previous one through the 72 hour period, then adjusted to the right to align more with the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 31.9N 24.9W 50 KT 60 MPH 12H 13/1800Z 31.7N 23.3W 50 KT 60 MPH 24H 14/0600Z 31.4N 21.3W 45 KT 50 MPH 36H 14/1800Z 31.1N 19.7W 45 KT 50 MPH 48H 15/0600Z 30.9N 18.5W 40 KT 45 MPH 60H 15/1800Z 31.1N 18.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 16/0600Z 32.1N 18.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 17/0600Z 36.0N 17.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 18/0600Z...DISSIPATED $$ Forecaster Roberts
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