[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 111439
TCDAT2

Tropical Storm Ophelia Discussion Number  10
NWS National Hurricane Center Miami FL       AL172017
1100 AM AST Wed Oct 11 2017

If I only had conventional satellite imagery, I would definitely
estimate that Ophelia was a hurricane. The cyclone has a ragged eye
surrounded by deep convection and cyclonically curved bands.
Furthermore, Dvorak intensity estimates, both subjective and
objective, from all agencies are T4.0 plus. However, several ASCAT
passes during the past day or so indicate that the winds have been
lower than the winds one could assign the cyclone by using Dvorak.
Once again this morning, a pair of ASCAT passes showed winds of
less than 45 kt, but I am assuming that the ASCAT can not resolve
the sharp wind gradient typically associated with an eyewall, and
earlier SSMIS data indicated that one is present. Since we do not
have a hurricane hunter plane to give us exact measurements, we
need to compromise between the very valuable satellite-based
estimates, and the initial intensity is set at 60 kt in this
advisory.

Although the ocean is not too warm, the shear is low and the
upper-troposphere is cool. These factors should provide some
low-octane fuel favoring slight strengthening, and Ophelia is
still expected to become a hurricane at any time within the next 12
hours. Extratropical transition is likely to start between day 3 and
day 4, and Ophelia is anticipated to remain a strong cyclone over
the northeastern Atlantic.

Ophelia is moving slowly toward the east at 3 kt, embedded within
light steering currents, and little motion is expected today. A
mid-level trough is forecast to amplify west of Ophelia, and this
pattern will provide a stronger southwesterly steering flow
which eventually force the cyclone to move toward the northeast with
increasing forward speed. Most of the track models agree with this
solution increasing the confidence in the track forecast. The NHC
forecast follows very closely the HFIP corrected consensus HCCA
which has been very skillful this season.


FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 30.0N  36.5W   60 KT  70 MPH
 12H  12/0000Z 29.9N  36.0W   65 KT  75 MPH
 24H  12/1200Z 30.1N  35.7W   70 KT  80 MPH
 36H  13/0000Z 30.8N  34.7W   70 KT  80 MPH
 48H  13/1200Z 31.5N  33.3W   70 KT  80 MPH
 72H  14/1200Z 34.0N  26.8W   70 KT  80 MPH
 96H  15/1200Z 40.0N  17.5W   70 KT  80 MPH...POST-TROP/EXTRATROP
120H  16/1200Z 51.5N  12.5W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Avila
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