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Issued at 400 AM CDT Mon Sep 13 2021 000 WTNT44 KNHC 130850 TCDAT4 Tropical Storm Nicholas Discussion Number 5 NWS National Hurricane Center Miami FL AL142021 400 AM CDT Mon Sep 13 2021 Radar data from Brownsville shows that the center of Nicholas is on the southwestern side of a large area of deep convection over the western Gulf of Mexico. While southwesterly shear continues to affect the storm, the radar presentation has recently improved, with what could be the start of a partial eyewall forming in the northern quadrant. The initial wind speed remains 50 kt based on earlier aircraft flight-level winds of 59 kt, believable SFMR values up to 50 kt, along with radar winds at 5000 ft near 60 kt. The storm is moving north-northwestward at about 12 kt. Nicholas is forecast to turn northward soon into a weakness in the subtropical ridge. The track prediction is only nudged slightly westward from the previous one through landfall, consistent with recent model guidance. Thereafter, there isn't good agreement among the models on how quickly the tropical cyclone will move northeastward out of Texas. Generally the models are faster this cycle, which seems believable given the large northward re-formation earlier likely exposing Nicholas to stronger mid-latitude flow. Thus the new NHC forecast is trended faster as well, but remains behind the model consensus. Obviously the forward speed is important to the heavy rainfall forecast, and this trend will be one to watch. Nicholas should continue to strengthen up until landfall due primarily to the very warm Gulf waters and the recent inner-core improvements. Moderate southwesterly shear and some dry air are the main inhibiting factors and will hopefully keep the strengthening in check. However, it is possible that Nicholas could become a hurricane before landfall, and that's the reason for the hurricane watch area. Nicholas should weaken after landfall, diminish into a tropical depression within a couple of days, and degenerate into a remnant low in about 3 days. No significant changes were made to the previous NHC wind speed prediction. Key Messages: 1. Heavy rainfall will impact portions of the Texas and Louisiana coasts through the middle of the week. Significant rainfall amounts are possible, potentially resulting in areas of considerable flash and urban flooding, especially in highly urbanized metropolitan areas. Isolated minor to moderate river flooding is also expected. 2. There is the danger of life-threatening storm surge inundation along the coast of Texas from Port Aransas to San Luis Pass. Residents in these areas should follow any advice given by local officials. 3. Nicholas is forecast to approach the middle Texas coast as a strong tropical storm today, and could be near hurricane intensity at landfall. Tropical storm conditions are expected along portions of the middle Texas coast beginning by this afternoon, with hurricane conditions possible from Port Aransas to Freeport this afternoon and tonight. 4. Tropical storm conditions are expected along portions of the northeastern coast of Mexico and the coast of south Texas beginning during the next few hours. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 25.5N 96.6W 50 KT 60 MPH 12H 13/1800Z 27.3N 96.8W 60 KT 70 MPH 24H 14/0600Z 29.2N 96.5W 45 KT 50 MPH...INLAND 36H 14/1800Z 30.6N 95.8W 35 KT 40 MPH...INLAND 48H 15/0600Z 31.5N 94.5W 30 KT 35 MPH...INLAND 60H 15/1800Z 32.1N 93.0W 25 KT 30 MPH...INLAND 72H 16/0600Z 32.5N 91.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 17/0600Z...DISSIPATED $$ Forecaster Blake

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