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Tropical Storm ORLENE Forecast Discussion Number 17
2016-09-15 04:52:28| National Hurricane Center (East Pacific)
Issued at 800 PM PDT WED SEP 14 2016 000 WTPZ41 KNHC 150252 TCDEP1 TROPICAL STORM ORLENE DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP162016 800 PM PDT WED SEP 14 2016 Orlene's convective signature remains a small, symmetric central dense overcast with some banding in the northern semicircle. However, the cloud top temperatures have warmed some and the extent of the cold cloudiness has diminished slightly during the last several hours. A blend of the TAFB/SAB subjective Dvorak, CIMSS Advanced Dvorak, and CIMSS/CIRA AMSU suggest that Orlene has weakened to a tropical storm with 60 kt as the initial intensity. Orlene is situated directly under the upper-level subtropical ridge and thus is experiencing very low vertical shear. However, the tropical storm is expected to ride along the 26C SST contour 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 blend of the LGEM/SHIPS statistical models and the COAMPS dynamical model, and is quite similar to that from the previous advisory. Perhaps the biggest uncertainty is when the 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-northwest at about 5 kt. The system is expected to turn toward the west or west-southwest and move faster for the next three to four days as mid-level ridging builds to its north. By day five, Orlene begins responding to the upper-level low that it approaches by turning toward the west-northwest. The NHC track forecast is slightly south of the previous advisory and is based upon the tightly clustered members of the multi-model TVCN consensus technique. A 0119Z AMSU pass allowed a modification of the 34 and 50 kt wind radii to be more asymmetric. The NHC wind radii forecast is based upon the multi-model RVCN consensus technique and is slightly smaller than that from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 20.4N 120.4W 60 KT 70 MPH 12H 15/1200Z 20.2N 121.5W 55 KT 65 MPH 24H 16/0000Z 20.0N 123.6W 50 KT 60 MPH 36H 16/1200Z 19.7N 125.9W 45 KT 50 MPH 48H 17/0000Z 19.6N 128.3W 40 KT 45 MPH 72H 18/0000Z 19.5N 133.6W 35 KT 40 MPH 96H 19/0000Z 20.0N 138.0W 30 KT 35 MPH 120H 20/0000Z 21.0N 142.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Landsea
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