[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 102039
TCDAT2

Tropical Storm Ophelia Discussion Number   7
NWS National Hurricane Center Miami FL       AL172017
500 PM AST Tue Oct 10 2017

The overall convective structure of Ophelia has improved markedly
over the past several, including the development of numerous,
tightly curved bands and a burst of deep convection near the center.
Upper-level anticyclonic outflow has also increased and expanded in
all quadrants. Dvorak satellite current intensity estimates are
T3.5/55 kt from TAFB and T4.0/65 kt from SAB, so the initial
intensity has been conservatively increased to 50 kt. A 28-30 kt
wind report from ship PBQL, located more 200 nmi northwest of the
center, indicates that the outer circulation is also strengthening.

The initial motion estimate is 135/04 kt. Ophelia is forecast to
continue moving southeastward at a slow but steady pace for the next
48 hours or so while the cyclone remains embedded within a broad
mid-/upper-level trough. The NHC model guidance remains in good
agreement on the Ophelia beginning to lift out to the northeast by
72 h, and then gradually accelerate into the mid-latitude westerlies
ahead of an eastward-moving mid-tropospheric trough. The latest
model guidance remains tightly packed, but it has also shifted
northward, which brings Ophelia closer to the Azores in the 96-120
hour period. However, the new forecast track was not shifted
northward and remains along the southern edge of the guidance
envelope between the NOAA HCCA consensus model and the more
southerly ECMWF model.

The GFS and ECMWF models continue to forecast only modest
intensification for the next 48-72 hours, despite the vertical wind
shear being fairly low at less than 10 kt. However, those models are
forecasting more vigorous strengthening after 96 h as Ophelia
experiences some baroclinic interaction, especially by 120 hours.
The strong baroclinic deepening on day 5 could be overdone somewhat
given that the best jetstream dynamics are forecast to be about 300
nmi northwest of the surface low and frontal zone. For now, the
official intensity forecast remains similar to the previous
advisory, and is little lower than the intensity consensus models
HCCA and IVCN and the GFS and ECMWF solutions on days 4 and 5.

FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 31.1N  38.0W   50 KT  60 MPH
 12H  11/0600Z 30.6N  37.5W   55 KT  65 MPH
 24H  11/1800Z 30.2N  36.8W   60 KT  70 MPH
 36H  12/0600Z 30.2N  36.4W   65 KT  75 MPH
 48H  12/1800Z 30.5N  35.6W   70 KT  80 MPH
 72H  13/1800Z 32.0N  32.2W   70 KT  80 MPH
 96H  14/1800Z 34.7N  25.8W   70 KT  80 MPH
120H  15/1800Z 39.0N  17.0W   70 KT  80 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart

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