531 WTNT44 KNHC 211440 TCDAT4 Potential Tropical Cyclone Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092023 1000 AM CDT Mon Aug 21 2023 The broad area of low pressure over the central Gulf of Mexico continues to gradually become better organized with showers and thunderstorms increasing on the system's north side. However, surface observations and early morning visible satellite images suggest that it does not have a well-defined center yet, and therefore, does not meet the definition of a tropical cyclone at this time. Since the system is forecast to strengthen and make landfall as a tropical storm on Tuesday, advisories are being initiated on Potential Tropical Cyclone Nine with Tropical Storm Warnings now in effect for portions of south Texas. The disturbance is moving fairly quickly to the west at 14 kt on the south side of a strong mid-level ridge located over the central U.S. An even faster motion to the west or west-northwest is expected, taking the system over southern Texas by midday Tuesday. It should be noted that since the system does not yet have a clear center, the details of the track forecast are a bit uncertain. The Air Force Hurricane Hunters are scheduled to investigate the system this afternoon, which should help assess the low-level structure. The environmental factors are generally favorable for the system to strengthen. However, there is limited time for the disturbance to take advantage of those conditions, especially since it still lacks a well-defined center. The NHC official intensity forecast shows the system reaching a peak intensity of 40 kt before landfall, which is near the high end of the model guidance. Rapid weakening is expected after landfall. KEY MESSAGES: 1. Heavy rainfall from Potential Tropical Cyclone Nine is expected across South Texas on Tuesday and Wednesday. The heavy rainfall may produce areas of flash and urban flooding. Across portions of Coahilla and Nuevo Leon in Mexico, flash flooding with possible landslides in mountainous terrain is expected Tuesday into Wednesday. 2. Coastal flooding is possible along the south Texas coast tonight through Tuesday morning. 3. Tropical storm conditions are expected in the warning area and are possible in the watch area beginning Tuesday morning. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 25.0N 89.9W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 22/0000Z 25.5N 92.8W 30 KT 35 MPH...TROPICAL CYCLONE 24H 22/1200Z 26.6N 96.8W 40 KT 45 MPH 36H 23/0000Z 27.8N 100.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 23/1200Z...DISSIPATED $$ Forecaster Cangialosi