000 WTPZ42 KNHC 180236 TCDEP2 TROPICAL DEPRESSION TWELVE-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP122014 800 PM PDT SUN AUG 17 2014 Visible satellite images indicate that the large area of low pressure located several hundred miles southwest of Mexico has acquired a well-defined center of circulation along with enough organized deep convection to qualify as a tropical cyclone. The initial intensity is set to 30 kt in agreement with a 28-kt ASCAT pass from 1754 UTC and a more recent 30 kt estimate from TAFB. Environmental conditions would seem to favor intensification due to warm waters ahead of the depression during the next few days and relatively low shear. The biggest negative factor is the initial structure of the cyclone, with a large radius of maximum wind and overall large sprawling circulation envelope. Tropical cyclones with this type of structure tend to intensify only gradually, and this is reflected in the NHC wind speed prediction below. The model guidance is also in relatively good agreement with the NHC forecast, with only the SHIPS model showing the depression reaching hurricane strength. The system should begin to weaken in a few days when it moves over much colder waters, although it could spin down more slowly than average due to its large size and a mid-latitude trough interaction. The best estimate of initial motion is 275/7. The subtropical ridge to the north of the cyclone is expected to remain for the next day or so, causing the depression to take a westward, then west-northwestward, course. However, an unusually deep trough for mid-August is forecast to dig just offshore of the southwestern United States, which will likely steer the tropical cyclone northward in two or three days, followed by a turn toward the northwest at long range as a result of a weakness left by the trough. Model guidance is in poor agreement at days 4 and 5 due to varying predicted strengths of the trough, with the ECMWF taking the cyclone significantly farther to the north of the rest of the models. Since the ECMWF ensemble mean is very close to the model consensus, for now the ECMWF operational solution is thought of as an outlier, and the NHC forecast is near the consensus at all forecast times. It is worth noting that while the official forecast is well offshore of the southwestern United States, model guidance does suggest a surge of moisture is possible in that region by Thursday. Please monitor products issued by your local National Weather Service office for more details on a possible heavy rain threat. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 16.1N 116.6W 30 KT 35 MPH 12H 18/1200Z 16.3N 117.7W 35 KT 40 MPH 24H 19/0000Z 16.7N 118.9W 40 KT 45 MPH 36H 19/1200Z 17.6N 119.5W 45 KT 50 MPH 48H 20/0000Z 18.4N 119.7W 50 KT 60 MPH 72H 21/0000Z 19.8N 120.0W 50 KT 60 MPH 96H 22/0000Z 22.4N 121.0W 45 KT 50 MPH 120H 23/0000Z 26.5N 124.5W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Blake