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Tropical Storm Ophelia Discussion Number 4
NWS National Hurricane Center Miami FL AL172017
1100 PM AST Mon Oct 09 2017
Ophelia's center is just south of a broad curved band of deep
convection. At synoptic time, the subjective Dvorak
classifications from TAFB and SAB were both at 2.5, or 35 kt, while
the CIMSS SATCON was at 43 kt. Given the increasingly curved
structure of the bands during the last couple of hours, the initial
intensity is set at 45 kt, a bit higher than the previous advisory.
While the tropical storm is fighting some moderate vertical shear
currently, the global models suggest that this should lighten some
between now and about day 4 as Ophelia resides between the
mid-latitude and subtropical westerlies. Even though the system
will be traversing cool 26C SSTs, upper-tropospheric temperatures
likely will also be cool, allowing for deep convection to continue.
The mid-level moisture analyzed in the SHIPS guidance appears to be
somewhat dry, though the total precipitable water imagery shows
distinct moistening near the system during the last couple of days.
The official intensity forecast shows gradual intensification
through day 3, then slow weakening thereafter. This is close to a
blend of the LGEM statistical guidance and the HWRF dynamical model
and is slightly above that of the previous advisory.
The initial position has fairly small uncertainty as the
low-level center is along the southern edge of the deep
convection, as seen in the GOES-16 shortwave infrared imagery.
Ophelia is moving toward the northeast at about 6 kt - somewhat
unexpectedly - this evening. Despite this, the model guidance
suggests that a ridge will soon build in strongly north of Ophelia
and force the tropical storm to the southeast and then south
during the next couple of days. Around day 3, Ophelia should get
kicked out toward the east-northeast by an approaching trough in the
mid-latitude westerlies. The official track forecast is north of
the previous forecast in the short term and east-northeast in the
long term, and is in between the HFIP Corrected Consensus Approach
(HCCA) and the previous forecast.
The initial tropical-storm-force wind radii was adjusted outward
based upon a 2137Z AMSU size analysis. The official size forecast
is based upon the RVCN consensus technique.
FORECAST POSITIONS AND MAX WINDS
INIT 10/0300Z 32.3N 39.0W 45 KT 50 MPH
12H 10/1200Z 32.5N 38.4W 50 KT 60 MPH
24H 11/0000Z 32.0N 38.1W 55 KT 65 MPH
36H 11/1200Z 31.1N 37.9W 65 KT 75 MPH
48H 12/0000Z 30.4N 37.5W 70 KT 80 MPH
72H 13/0000Z 30.8N 35.5W 75 KT 85 MPH
96H 14/0000Z 32.5N 32.0W 70 KT 80 MPH
120H 15/0000Z 34.5N 26.5W 60 KT 70 MPH