000 WTPZ43 KNHC 050246 TCDEP3 Tropical Depression Eighteen-E Discussion Number 3 NWS National Hurricane Center Miami FL EP182021 1000 PM CDT Thu Nov 04 2021 TD18-E is a poorly organized system this evening. Most of the deeper convection that was near the center earlier today has collapsed, with only a few skeletal outer bands remaining south of the low-level circulation. Last light visible satellite imagery also indicated that the low-level center was not vertically aligned, located to the west ahead of the mid-level center. While I have yet to receive new scatterometer data which should be arriving soon, the current satellite structure argues against any development. Indeed, the latest TAFB and SAB Dvorak satellite estimates have held steady or decreased from earlier today. The current intensity will remain at 30 kt for this advisory, and even this might be a bit generous. After a motion to the west-northwest earlier, the depression appears to have resumed a due westward motion, estimated at 270/6 kt. A narrow mid-tropospheric ridge north of the cyclone has been steering the system slowly westward, and this ridge is expected to strengthen and merge with a larger mid-level ridge currently centered over the Baja California peninsula. The end result of this pattern reconfiguration on the depression should be a faster motion to the west, or even west-southwest due to the orientation of the ridge complex. By the end of the forecast period, the ridge is expected to shift a bit more to the east, which will provide an opportunity for the depression to gain some latitude by the end of the forecast period. The model track guidance continues to be in good agreement, though with a bit of along-track spread. The guidance overall has made another shift to the south this cycle, and the latest NHC track was also once again nudged further south, staying on the northern side of the guidance envelope but not too far from the TVCE and HCCA consensus solutions. The intensity forecast is somewhat challenging. While the latest SHIPS guidance indicates the depression will remain in low 200-850 hPa vertical wind shear, have ample mid-level moisture, and be over 27-28 C sea-surface temperatures, the majority of the intensity guidance shows only modest strengthening over the next 2-3 days. Model-derived soundings from the GFS and HWRF suggest that higher mid-level shear could be undercutting this favorable upper-level flow pattern over the time period. This undercutting shear may help explain why the low and mid-level centers of the depression are currently not aligned. In addition, surface-based backwards trajectories suggest that the tropical cyclone is ingesting air originating over the equator, which currently is dominated by an environment of stable stratocumulus clouds. This may help explain the anemic convective appearance of the system currently. An additional forecast concern is the low-latitude track of the cyclone, with the forecast showing the system losing additional latitude over the next several days. All these factors make me skeptical that there will be significant intensification over the next 2-3 days and the intensity forecast has been lowered somewhat from the previous one over this time period. The latest NHC intensity forecast is a bit under the latest IVCN and NOAA-HCCA consensus, but is higher than the current LGEM and ECMWF guidance, which essentially show no intensification through the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 9.7N 91.2W 30 KT 35 MPH 12H 05/1200Z 9.6N 92.0W 30 KT 35 MPH 24H 06/0000Z 9.2N 93.5W 30 KT 35 MPH 36H 06/1200Z 9.1N 95.4W 35 KT 40 MPH 48H 07/0000Z 8.9N 97.4W 35 KT 40 MPH 60H 07/1200Z 8.9N 99.5W 35 KT 40 MPH 72H 08/0000Z 9.3N 102.0W 40 KT 45 MPH 96H 09/0000Z 10.0N 106.7W 50 KT 60 MPH 120H 10/0000Z 10.6N 111.5W 55 KT 65 MPH $$ Forecaster Papin