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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