000 WTPZ43 KNHC 052045 TCDEP3 Tropical Depression Eighteen-E Discussion Number 6 NWS National Hurricane Center Miami FL EP182021 400 PM CDT Fri Nov 05 2021 For the last 6-9 hours, TD18-E has not produced enough organized deep convection to be classifiable as a tropical cyclone. Indeed, the current satellite structure primarily consists of a low-level cloud swirl, with only a few disorganized puffs of colder cloud tops that quickly decay after they form. In addition, an earlier ASCAT-B pass valid at 1608 UTC suggested that the circulation was also becoming increasingly fragile, with less than 10 kt winds on the southwest side of the vortex and a peak wind retrieval of only 25 kt. Subjective satellite Dvorak estimates have been decreasing, with the latest T numbers down to T1.5 from TAFB and T1.0 from SAB. Assuming some undersampling could still be occuring from the earlier ASCAT wind data, the intensity was held at 30 kt this advisory, though this is likely generous. The motion continues to be south of due west, with the latest estimate now at 260/9 kt. There has not been much change to the latest track reasoning. An expansive mid-level ridge is expected to build eastward over Mexico over the next several days, helping to maintain the tropical cyclone on a westward heading throughout the forecast period. However, the cyclone is vertically shallow, and the influence of the low-level gap wind flow emanating from the Gulf of Tehuantepec could be causing the short-term south of due west bend in the track. Yet again, the track guidance has come in further south and a bit faster compared to the previous cycle, and the latest NHC track forecast has been shifted in that direction, though still not quite as far south and west as the HCCA and TVCE consensus aids. Without any organized convection occuring near the center of the depression currently, its future status as a tropical cyclone could be in jeopardy. Apparently stable air has infiltrated the circulation and is limiting convective output despite sufficently warm sea-surface temperatures and vertical wind shear that does not seem too inhibiting. The GFS, ECMWF, and HWRF model simulated IR brightness temperature forecasts suggest that better organized convection should return near the low-level center during tonight's diurnal maximum. Even so, the global model guidance continues to trend downward in the intensity forecast, delaying intensification further out into the future. Indeed the most recent GFS run maintains status quo intensity over the next 48 hours, joining the ECMWF, SHIPS and LGEM guidance. The only guidance that shows significant intensification over the next several days is the HWRF and this model has had a persistent high bias. The latest intensity forecast has been lowered a bit more beyond 36 h. As alluded above, if organized deep convection does not return soon, it's possible this depression could degenerate into a remnant low as early as tomorrow. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 9.1N 93.5W 30 KT 35 MPH 12H 06/0600Z 8.9N 94.7W 30 KT 35 MPH 24H 06/1800Z 8.6N 96.7W 30 KT 35 MPH 36H 07/0600Z 8.4N 99.0W 30 KT 35 MPH 48H 07/1800Z 8.7N 101.3W 30 KT 35 MPH 60H 08/0600Z 9.2N 103.6W 35 KT 40 MPH 72H 08/1800Z 9.6N 106.3W 40 KT 45 MPH 96H 09/1800Z 10.6N 111.1W 45 KT 50 MPH 120H 10/1800Z 11.0N 116.0W 50 KT 60 MPH $$ Forecaster Papin