[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 100839
TCDAT5

TROPICAL STORM NICOLE DISCUSSION NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152016
500 AM AST MON OCT 10 2016

Nicole's overall convective pattern has changed little since the
previous advisory, with most of the convection located in the
eastern semicircle. However, during the past hour or two, a small
burst of deep convection with tops to -80C has developed just east
of the exposed low-level circulation center, signaling that dry air
entrainment into the center of the cyclone has abated somewhat.
Satellite current intensity (CI) estimates from TAFB and SAB remain
55 kt, and a late-arriving ASCAT-A pass indicated 45-kt surface
winds in the western semicircle where no convection was present.
Based on these data, the initial intensity remains 55 kt.

Nicole is moving slowly northward and the initial motion estimate is
360/05 kt. The cyclone is expected to move slowly at around 5 kt for
the next 72 hours, beginning with a motion toward the north today,
followed by a turn to the north-northwest tonight, and a turn toward
the northwest on Tuesday. By 36-48 hours, a break in the ridge to
the north of Nicole is forecast to develop as a shortwave trough
moves off of the U.S. east coast and erodes the blocking ridge. This
should allow Nicole to move northward by 48 hours and turn toward
the north-northeast and northeast by 72 hours. By 96 hours and
beyond, the aforementioned shortwave trough is forecast to capture
the cyclone and accelerate Nicole to the northeast over the north
Atlantic. The global models are now in excellent agreement on this
developing track scenario, but have unfortunately shifted farther
west and are now much closer to Bermuda. The new NHC track forecast
has been shifted westward as a result, but still lies east of the
consensus model TVCN and the GFS-ECMWF solutions, which bring
Nicole over or just west of Bermuda in about 84 hours.

The combination of northerly shear and some additional modest dry
air entrainment is expected to inhibit development today. However,
by Tuesday the vertical wind shear is forecast by the GFS and ECMWF
models to decrease to less than 10 kt, and remain low until about 72
hours. The low shear conditions and developing upper-level outflow
pattern as depicted in the global and regional models, along with
Nicole's already robust low- to mid-level circulations, should allow
the cyclone to strengthen and regain hurricane status during that
time. By 96 hours and beyond, southwesterly shear ahead of the
shortwave trough is forecast to increase to 30-40 kt, which should
induce steady weakening. Extratropical transition is possible by 120
hours, but most of the intensity guidance maintains Nicole as a
tropical cyclone, which is reflected in the official forecast. The
new intensity forecast closely follows the SHIPS intensity model,
which appears to have a good handle on the timing of the reduction
of the vertical shear and associated strengthening, and also remains
above the intensity consensus model IVCN.

The 34-kt wind radius was expanded in the northeastern quadrant
based on 31-33 kt winds recently reported by NOAA Buoy 41049.

FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 25.0N  65.2W   55 KT  65 MPH
 12H  10/1800Z 25.8N  65.3W   55 KT  65 MPH
 24H  11/0600Z 26.6N  65.7W   60 KT  70 MPH
 36H  11/1800Z 27.2N  66.2W   65 KT  75 MPH
 48H  12/0600Z 27.8N  66.8W   75 KT  85 MPH
 72H  13/0600Z 30.5N  66.0W   85 KT 100 MPH
 96H  14/0600Z 34.5N  62.2W   80 KT  90 MPH
120H  15/0600Z 38.5N  56.3W   70 KT  80 MPH

$$
Forecaster Stewart
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