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Tropical Storm Nicholas Forecast Discussion Number 11
2021-09-14 22:56:07| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Tue Sep 14 2021 000 WTNT44 KNHC 142056 TCDAT4 Tropical Storm Nicholas Discussion Number 11 NWS National Hurricane Center Miami FL AL142021 400 PM CDT Tue Sep 14 2021 Doppler weather radar data from Houston and Lake Charles, along with surface observations, indicate that the intensity of Nicholas has remained steady over the past several hours despite having moved a little farther inland over the upper Texas coastal plain. Both satellite and radar data also indicate that the overall circulation has tightened up somewhat, although a large swath of stable low clouds have advected into most of the southern semicircle of Nicholas' circulation. The highest sustained wind speeds of 34-36 kt have occurred in a narrow band of fragmented, shallow convection between Sabine Pass, Texas, and Cameron, Louisiana, during the past couple of hours. Doppler radar velocity data from Lake Charles has also indicated wind speeds of 40-45 at 3,000 ft altitude just offshore the southwestern coast of Louisiana. Based on these wind data, the initial intensity is set at 35 kt. The estimated central pressure of 1003 mb is based on nearby surface observations, especially the reports from the Eagle Point, Texas, C-MAN station, which indicate that the center of Nicholas passed over or near that station between 1800-1900 UTC. As Nicholas moves farther inland, gradual weakening is forecast due to land interaction, entrainment of drier and more stable low- and mid-level air, and strong westerly vertical wind shear in excess of 30 kt. Nicholas is forecast to become a tropical depression later this evening and degenerate into a remnant low by late Wednesday or early Thursday. The initial motion estimate is east-northeastward or 070 degrees at 5 kt. Nicholas is forecast by most of the global and regional models continue its east-east-northeastward motion through tonight, followed by an eastward motion at a slower forward speed on Wednesday and Thursday. Nicholas could still stall over southwestern or central Louisiana as the low-level steering flow collapses on Thursday. The new NHC track forecast is similar to the previous advisory track, and lies near the consensus track models TCVA and NOAA-HCCA. Although the winds associated with Nicholas will gradually subside, heavy rainfall and a significant flash flood risk will continue along the Gulf Coast for the next couple of days. Key Messages: 1. Heavy rainfall will impact areas across southern and central Louisiana, southern Mississippi, far southern Alabama, and the western Florida Panhandle through early Friday. Significant rainfall amounts are expected, potentially resulting in areas of life-threatening flash and urban flooding across these areas. Widespread minor to isolated moderate river flooding is also possible. 2. Storm surge inundation along the coasts of upper Texas and southwestern Louisiana will gradually diminish into tonight. 3. Tropical storm conditions in the warning area long portions of the upper Texas and southwestern Louisiana coasts will gradually subside by this evening. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 29.6N 94.6W 35 KT 40 MPH...INLAND 12H 15/0600Z 29.8N 94.0W 25 KT 30 MPH...INLAND 24H 15/1800Z 30.0N 93.2W 25 KT 30 MPH...INLAND 36H 16/0600Z 30.1N 92.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 16/1800Z 30.5N 92.4W 15 KT 15 MPH...POST-TROP/REMNT LOW 60H 17/0600Z 30.9N 92.4W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 17/1800Z...DISSIPATED $$ Forecaster Stewart
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