[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 140234
TCDAT5

HURRICANE NICOLE DISCUSSION NUMBER  40
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152016
1100 PM AST THU OCT 13 2016

The satellite presentation of Nicole has degraded substantially this
evening, with the area of cold convective tops shrinking in size and
become less symmetric.  The low-level center is difficult to locate
in geostationary imagery, but recent microwave data suggest it is
located to the southwest of the coldest convective tops.  This
structure is consistent with the 40-45 kt of southwesterly shear
analyzed over Nicole by the SHIPS model and UW-CIMSS.  The initial
intensity has been lowered to 85 kt, which is between the latest
Dvorak estimates from TAFB and SAB.

Nicole should continue to weaken in the next 12 hours due to the
persistent strong shear and cooling SSTs.  However, from 24-48
hours, forcing associated with a shortwave trough should cause
Nicole to remain a powerful cyclone, and the intensity is maintained
at 75 kt through that time.  After the shortwave moves past Nicole,
slow decay is expected late in the period.  The new NHC intensity
forecast is lower than the previous one in the first 12-24 hours,
following the trend of the latest hurricane intensity guidance.
After that time, the intensity forecast is based on global model
guidance.  Note that the structure of Nicole is quite uncertain
during the forecast period, since the cyclone does not appear to
complete extratropical transition, with the global models showing
the cyclone acquiring a warm seclusion structure.

A 2201Z WindSat pass suggested that the center of Nicole was located
a little south of previous estimates.  The initial motion is
estimated to be 060/18, as Nicole is now embedded in the mid-
latitude southwesterly flow ahead of a longwave trough moving off
the U.S. east coast.  This pattern should steer Nicole generally
east-northeastward for the next 48 hours, although the forward speed
will decrease by 36 hours as Nicole interacts with the
aforementioned shortwave.  The trough moves east of Nicole by 72
hours, leaving the cyclone in a region of weaker steering flow until
a high-latitude trough approaches from the northwest in 4-5 days,
and cause Nicole to accelerate northeastward by the end of the
forecast period.  The new NHC track forecast is a little south of
the previous one due to the initial position and is close to a blend
of the GFS and ECMWF models through the period.

The post-tropical portion of Nicole's track, intensity, and wind
radii forecast has been coordinated with the NOAA Ocean Prediction
Center.

Note that swells from Nicole will affect Bermuda and portions of
the U.S. east coast and Atlantic Canada during the next couple of
days.  By early next week, wave models suggest that long-period
swell from Nicole will radiate outward and affect much of the
North Atlantic basin.

FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 34.4N  61.2W   85 KT 100 MPH
 12H  14/1200Z 35.6N  58.5W   75 KT  85 MPH
 24H  15/0000Z 36.9N  54.3W   75 KT  85 MPH
 36H  15/1200Z 38.1N  51.0W   75 KT  85 MPH
 48H  16/0000Z 38.6N  49.0W   75 KT  85 MPH...POST-TROPICAL
 72H  17/0000Z 39.0N  47.0W   65 KT  75 MPH...POST-TROPICAL
 96H  18/0000Z 41.0N  44.0W   65 KT  75 MPH...POST-TROPICAL
120H  19/0000Z 47.0N  37.0W   60 KT  70 MPH...POST-TROPICAL

$$
Forecaster Brennan

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