000 WTPZ41 KNHC 150832 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 200 AM PDT THU SEP 15 2016 Orlene has a quite small, symmetric central dense overcast tonight, with a tiny eye occasionally making an appearance. Overall, the convective structure has not changed much over the last few hours. A blend of the TAFB/SAB subjective Dvorak and CIMSS Advanced Dvorak suggests that Orlene remains a 60-kt tropical storm. Orlene is situated directly under an upper-level subtropical ridge and thus is experiencing very low vertical shear. However, the tropical storm is expected to ride along the 26C SST isotherm while the not-very-moist environment becomes quite dry during the next three days. In addition, by days four and five, the shear should go up substantially as Orlene approaches a mid- to upper-level low. The bottom line is that the tropical storm should gradually weaken. The NHC intensity forecast is based upon a now more tightly clustered set of statistical and dynamical model guidance. Perhaps the biggest uncertainty is when Orlene's deep convection will cease. The forecast is for that to occur around day five, but it would not be surprising if this occurred significantly earlier. Orlene is moving toward the west at about 6 kt. The system is expected to move toward the west or west-southwest with a faster forward speed during the next three to four days as mid-level ridging builds to its north. Around day four or five, Orlene should begin responding to the upper-level low that it approaches by turning toward the west-northwest. The NHC track forecast is nearly unchanged and is based upon the tightly clustered members of the multi-model TVCN consensus technique. A pair of ASCAT scatterometer passes indicate that Orlene has contracted some in size for its 34 and 50 kt wind radii. The NHC wind radii forecast is based upon the multi-model RVCN consensus technique and is slightly smaller than that from the previous advisory because of the smaller initial size. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 20.1N 121.2W 60 KT 70 MPH 12H 15/1800Z 19.9N 122.5W 55 KT 65 MPH 24H 16/0600Z 19.6N 124.6W 50 KT 60 MPH 36H 16/1800Z 19.5N 126.9W 45 KT 50 MPH 48H 17/0600Z 19.5N 129.4W 40 KT 45 MPH 72H 18/0600Z 19.5N 134.5W 35 KT 40 MPH 96H 19/0600Z 20.0N 139.0W 30 KT 35 MPH 120H 20/0600Z 21.0N 143.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Landsea