000 WTPZ43 KNHC 152052 TCDEP3 Tropical Depression Thirteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP132022 400 PM CDT Thu Sep 15 2022 Visible satellite imagery and a couple of recent partial ASCAT overpasses indicate that the circulation associated with the area of low pressure located south of the Gulf of Tehuantepec has become better defined. A curved band of convection is located over the western and southwestern portions of the circulation and has enough organization to designate the system as a tropical depression. The ASCAT-C instrument measured peak winds of 25-27 kt over the southeastern portion of the circulation and since stronger winds likely exist within the convection, the initial intensity is set at 30 kt. This is a little above the latest Dvorak estimate of T1.5 (25 kt) from TAFB. Since the cyclone is still in its formative stage, the initial motion is a highly uncertain 310/3 kt. The depression is forecast to move generally northwestward during the next few days around the eastern portion of monsoonal flow that is established over the eastern Pacific south of Mexico. As this flow strengthens during the next day or so, the depression should move northwestward at an increasingly faster forward speed, and the center of the cyclone is forecast to approach the southern coast of Mexico on Saturday. The GFS and ECMWF models have come into better agreement on the general heading of the system, but there are some differences regarding how much the cyclone accelerates. The ECMWF is on the faster side of the guidance and brings the center onshore about 6-12 hours sooner than the GFS. The NHC track is between these solutions and is along the eastern side of the model trackers. It should be noted that the global model trackers appear to be latching onto another low-level vorticity center that is embedded within the monsoonal flow after 48 hours. As a result, the NHC track forecast more closely follows the model fields from the various global models. The depression is located over warm waters and within a moist environment, however moderate northeasterly shear is forecast to persist over the system during the next couple of days. This shear is likely to prevent significant intensification, but gradual strengthening is anticipated. The NHC forecast calls for the depression to become a tropical storm tonight or Friday and shows some additional modest increase in strength before the center reaches the coast. Rapid weakening should occur after landfall. The NHC intensity forecast is a little below the SHIPS model and IVCN consensus aids due to the current broad wind field and expected shear conditions. Based on this forecast, the government of Mexico has issued a tropical storm watch for a portion of the coast of southern Mexico. Key Messages: 1. Heavy rains will reach portions of coastal southern Mexico on Friday, increasing in coverage and intensity by Saturday and Saturday night. This rainfall may produce flash and urban flooding, along with isolated mudslides in areas of higher terrain. 2. Tropical storm conditions are possible along the coast of southern Mexico between Laguna de Chacahua and Zihautenajo beginning on Saturday and a Tropical Storm Watch has been issue for that area. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 12.7N 95.4W 30 KT 35 MPH 12H 16/0600Z 13.3N 96.1W 35 KT 40 MPH 24H 16/1800Z 14.1N 97.4W 40 KT 45 MPH 36H 17/0600Z 15.1N 98.8W 45 KT 50 MPH 48H 17/1800Z 16.9N 100.5W 50 KT 60 MPH 60H 18/0600Z 18.4N 101.9W 30 KT 35 MPH...INLAND 72H 18/1800Z...DISSIPATED $$ Forecaster Brown