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Tropical Depression Fifteen-E Forecast Discussion Number 3
2017-09-12 10:38:24| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Tue Sep 12 2017 000 WTPZ45 KNHC 120838 TCDEP5 Tropical Depression Fifteen-E Discussion Number 3 NWS National Hurricane Center Miami FL EP152017 200 AM PDT Tue Sep 12 2017 Shortwave and BD-curve infrared imagery earlier showed a deep convective burst with -70C cold tops near the surface center. That convective mass has since been displaced about 90 miles west of the exposed center and has warmed and diminished. Therefore, the initial intensity is held at 25 kt and agrees with the Dvorak intensity estimates from SAB and TAFB. The intensity forecast has become a bit problematic. Earlier SHIPS model runs indicated that the shear would either persist or increase. The latest run, however, reveals the shear decreasing considerably after 48 hours. On the other hand, the GFS, ECMWF, and the LGEM intensity guidance all show the depression gradually weakening and becoming a remnant low in 5 days or less, while the UKMET strengthens the cyclone to a tropical storm around day 3. A third scenario is indicated in the HFIP Corrected Consensus (HCCA) technique, which is similar to the GFS, ECMWF and the LGEM, but shows dissipation in less than 48 hours. The NHC forecast reflects some increase in intensity at the 24 hour period, but after that time, it shows weakening to a remnant low in 3 days, out of respect for the GFS and ECMWF global models, the LGEM, and the HFIP Corrected Consensus (HCCA) technique. The motion is estimated to be westward, or 260/13 kt. A low- to mid-level subtropical ridge extending over the eastern Pacific from the Baja California peninsula is forecast to build slightly southwestward later today influencing the depression to turn west-southwestward. At the 36 hour period, the cyclone should gradually turn back toward the west followed by a northwestward motion around 72 hours in response to an increasing weakness in the ridge along 123W. Around day 4, the depression is forecast to turn back toward the west within the low-level trade wind flow. The official forecast is slightly south of the previous forecast and is in the middle of the ECMWF and HCCA solutions. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 15.8N 115.1W 25 KT 30 MPH 12H 12/1800Z 15.5N 116.9W 25 KT 30 MPH 24H 13/0600Z 15.1N 118.8W 30 KT 35 MPH 36H 13/1800Z 15.1N 120.4W 30 KT 35 MPH 48H 14/0600Z 15.3N 121.6W 25 KT 30 MPH 72H 15/0600Z 15.9N 123.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 16/0600Z 15.9N 125.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 17/0600Z...DISSIPATED $$ Forecaster Roberts
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