1. Heavy rainfall will impact portions of southeastern Texas, Louisiana, and southern Mississippi through the middle of the week. Significant rainfall amounts are possible, potentially resulting in areas of life-threatening flash and urban flooding, especially in highly urbanized metropolitan areas. Minor to isolated moderate river flooding is also expected, along with isolated major river flooding across smaller river basins and urban areas.

2. There is the danger of life-threatening storm surge inundation along the coast of Texas from Port Aransas to Sabine 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 this evening, and could be near hurricane intensity at landfall. Tropical storm conditions are expected along portions of the middle and upper Texas coasts this evening and tonight, with hurricane conditions possible from Port Aransas to San Luis Pass.

CHANGES WITH THIS ADVISORY: The Tropical Storm Warning has been discontinued south of Baffin Bay, Texas. The Storm Surge Watch from Baffin Bay to Port Aransas, Texas, including Corpus Christi Bay has been discontinued. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for...
- Port Aransas Texas to Sabine Pass
- Galveston Bay, Aransas Bay, San Antonio Bay, and Matagorda Bay A Hurricane Watch is in effect for...
- Port Aransas to San Luis Pass Texas A Tropical Storm Warning is in effect for...
- Baffin Bay to Sabine Pass A Storm Surge Watch is in effect for...
- Sabine Pass to Rutherford Beach Louisiana A Storm Surge Warning means there is a danger of life threatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a life threatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials. A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area. A Storm Surge Watch means there is a possibility of life threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. A Hurricane Watch means that hurricane conditions are possible within the watch area. Interests elsewhere in southwestern Louisiana should monitor the progress of Nicholas. For storm information specific to your area, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office.

Key messages for Nicholas can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4, WMO header WTNT44 KNHC and on the web at hurricanes.gov/graphics_at4.shtml?key_messages

RAINFALL: Nicholas is expected to produce storm total rainfall of 6 to 12 inches, with isolated maximum amounts of 18 inches, across portions of the middle and upper Texas coastal areas through Wednesday. Life threatening flash flooding impacts, especially in highly urbanized metropolitan areas, are possible across portions of the upper Texas Gulf Coast and far southwestern Louisiana. Across interior southeast Texas into southern central Louisiana and southern Mississippi, rainfall totals of 4 to 8 inches with locally higher amounts near 10 inches are expected through Thursday. This rainfall may produce areas of considerable flash and urban flooding. The potential for minor to isolated moderate river flooding exists across the entire region, along with isolated major river flooding, especially in the smaller river basins and urban areas.

STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide... Port O'Connor, TX to San Luis Pass including Matagorda Bay...3 5 ft San Luis Pass to Rutherford Beach, LA including Galveston Bay...2 4 ft Port Aransas, TX to Port O'Connor, TX...2 4 ft Aransas Bay and San Antonio Bay...2 4 ft Rutherford Beach, LA to Intracoastal City, LA...1 3 ft Sabine Lake and Calcasieu Lake...1 3 ft Baffin Bay to Port Aransas, TX...1 3 ft Corpus Christi Bay...1 3 ft Mouth of the Rio Grande to Baffin Bay...1 2 ft The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and dangerous waves. Surge related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office.

WIND: Tropical storm conditions are expected within the warning area across central and upper Texas coasts through tonight, making outside preparations difficult or dangerous. Hurricane conditions are possible in the Hurricane Watch area as early as this evening.

TORNADOES: A couple of tornadoes will be possible through tonight, mainly along the upper Texas coast.

SURF: Swells generated by Nicholas will continue affecting portions of the northwest Gulf coast through Tuesday. These swells are likely to cause life threatening surf and rip current conditions. Please consult products from your local weather office.

At 400 PM CDT (2100 UTC), the center of Tropical Storm Nicholas was located by NOAA Doppler weather radars near latitude 27.4 North, longitude 96.4 West. Nicholas is moving toward the north northeast near 12 mph (19 km/h) and this general motion is expected to continue through tonight, followed by a turn toward the northeast by late Tuesday. On the forecast track, the center of Nicholas is expected to make landfall along the central Texas coast later tonight. Data from NOAA Doppler weather radars and an earlier reconnaissance flight indicate that maximum sustained winds have increased to near 65 mph (100 km/h) with higher gusts. Some additional strengthening is forecast this afternoon and evening, and Nicholas could be near hurricane strength when it reaches the central Texas coast. Weakening is anticipated on Tuesday and Wednesday while Nicholas moves over land. Tropical storm force winds extend outward up to 115 miles (185 km) from the center. During the past couple of hours, NOAA buoy 42019 located about 75 miles northeast of the center, reported a sustained wind of 45 mph (72 km/h) and a gust to 56 mph (91 km/h). The estimated minimum central pressure is 1000 mb (29.53 inches).

Earlier reconnaissance aircraft flight-level wind data, along with recent Doppler radar velocity data from Brownsville and Corpus Christi, indicate that the inner-core wind field has still not consolidated into a single low-level wind center. High-resolution 1-minute GOES-16 visible satellite imagery, radar data, and reconnaissance wind data all indicate at least three small but very tight swirls revolving counter-clockwise around a mean center. An eye feature has tried to form on multiple occasions, only to dissipate after less than half an hour. An Air Force Reserve Hurricane Hunter aircraft sampled the most of the northeastern quadrant of Nicholas' larger circulation this morning and afternoon, and measured 63-67-kt 850-mb flight-level winds, which roughly equals 53-54-kt surface winds in that quadrant; the aircraft also found SFMR surface winds of 50-51 kt in the same area. In addition, Doppler velocity data from Corpus Christi and Brownsville have been indicating average velocities of 59-60 kt between 9,000-10,000 ft near the center, which also equates to about 53-54-kt surface winds. Based on these wind data, the advisory intensity has been increased to 55 kt.

The initial motion estimate is 015/10 kt. The new NHC model guidance has come into better agreement on Nicholas moving toward the north- northeast until landfall occurs, now that the 12Z ECMWF model has made a significant eastward shift closer to the previous and current GFS and HWRF model solutions. After landfall, Nicholas is expected to move around the northwestern periphery of a deep-layer subtropical ridge that is oriented east-to-west across the central and eastern Gulf of Mexico. The latest guidance has continued to trend more eastward through 24 hours, followed by a more southward or right-of-track trend thereafter. As a result, the new NHC track forecast has followed suit, and has also been shifted a little to the right of the previous advisory track, and lies between the tightly packed consensus models to the west and the GFS model to the east.

Doppler velocity data from the Houston WSR-88D radar has shown a large swath of hurricane-force wind speed speeds in the northeastern quadrant of Nicholas' circulation above 12,000 ft during the past couple of hours, with brief appearances of average velocities of 80-100 kt at high altitudes. Thus, there is an abundance of large-scale cyclonic vorticity available for another burst of intense convection to tap into, which could allow Nicholas to approach hurricane strength by landfall. This would most likely occur tonight during the convective maximum period near landfall where increased frictional convergence along the coast could aid in the development of convection on the west side of the circulation. After landfall, rapid weakening is expected owing to land interaction, strong southwesterly vertical wind shear in excess of 30 kt, and entrainment of mid-level dry air from the southern Plains. As a result of these negative conditions, Nicholas is forecast to weaken to tropical depression by late Tuesday and degenerate into a remnant low on Wednesday.

Corrected third paragraph typo

Earlier reconnaissance aircraft flight-level wind data, along with recent Doppler radar velocity data from Brownsville and Corpus Christi, indicate that the inner-core wind field has still not consolidated into a single low-level wind center. High-resolution 1-minute GOES-16 visible satellite imagery, radar data, and reconnaissance wind data all indicate at least three small but very tight swirls revolving counter-clockwise around a mean center. An eye feature has tried to form on multiple occasions, only to dissipate after less than half an hour. An Air Force Reserve Hurricane Hunter aircraft sampled the most of the northeastern quadrant of Nicholas' larger circulation this morning and afternoon, and measured 63-67-kt 850-mb flight-level winds, which roughly equals 53-54-kt surface winds in that quadrant; the aircraft also found SFMR surface winds of 50-51 kt in the same area. In addition, Doppler velocity data from Corpus Christi and Brownsville have been indicating average velocities of 59-60 kt between 9,000-10,000 ft near the center, which also equates to about 53-54-kt surface winds. Based on these wind data, the advisory intensity has been increased to 55 kt.

The initial motion estimate is 015/10 kt. The new NHC model guidance has come into better agreement on Nicholas moving toward the north- northeast until landfall occurs, now that the 12Z ECMWF model has made a significant eastward shift closer to the previous and current GFS and HWRF model solutions. After landfall, Nicholas is expected to move around the northwestern periphery of a deep-layer subtropical ridge that is oriented east-to-west across the central and eastern Gulf of Mexico. The latest guidance has continued to trend more eastward through 24 hours, followed by a more southward or right-of-track trend thereafter. As a result, the new NHC track forecast has followed suit, and has also been shifted a little to the right of the previous advisory track, and lies between the tightly packed consensus models to the west and the GFS model to the east.

Doppler velocity data from the Houston WSR-88D radar has shown a large swath of hurricane-force wind speeds in the northeastern quadrant of Nicholas' circulation above 12,000 ft during the past couple of hours, with brief appearances of average velocities of 80-100 kt at high altitudes. Thus, there is an abundance of large-scale cyclonic vorticity available for another burst of intense convection to tap into, which could allow Nicholas to approach hurricane strength by landfall. This would most likely occur tonight during the convective maximum period near landfall where increased frictional convergence along the coast could aid in the development of convection on the west side of the circulation. After landfall, rapid weakening is expected owing to land interaction, strong southwesterly vertical wind shear in excess of 30 kt, and entrainment of mid-level dry air from the southern Plains. As a result of these negative conditions, Nicholas is forecast to weaken to tropical depression by late Tuesday and degenerate into a remnant low on Wednesday.