[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 162045
TCDAT5

HURRICANE NICOLE DISCUSSION NUMBER  51
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152016
500 PM AST SUN OCT 16 2016

Nicole's 70 nmi wide ragged eye remains distinct, surrounded by a
nearly closed ring of convection consisting of cloud tops of -45C to
-55C. However, the overall cloud pattern is beginning to look more
like an extratropical low pressure system than that of a tropical
cyclone. The initial intensity has been lowered to 70 kt, which is
closer to the latest subjective and objective Dvorak intensity
estimate of T4.0/65 kt from both TAFB and NHC.

Nicole appears to have finally made the much anticipated turn to the
northeast, and is now moving 045/08 kt. Nicole currently is trapped
between two high-amplitude ridges -- one located offshore of eastern
Canada and the other to the west of Europe. The latest 12Z model
guidance remains in excellent agreement on this blocking ridge
pattern breaking down over the next few days as a strong shortwave
trough currently located over northeastern Canada moves quickly
eastward. The increasing southwesterly deep-layer flow ahead of the
trough should begin to accelerate Nicole northeastward tonight and
Monday, and then turn the cyclone north-northeastward over the far
North Atlantic on Tuesday. The track models are in very good
agreement on this developing track scenario, so the new NHC forecast
track is essentially just an extension of the previous advisory
track, and lies close to a blend of the various consensus models and
input from the NOAA Ocean Prediction Center (OPC) at 48-72h.

Although Nicole is currently located over marginal sea surface
temperatures of about 24 deg C, it is beneath a region of unusually
cold upper-tropospheric temperatures, creating an unstable condition
barely sufficient to support convection in the inner-core region of
the cyclone. However, the latest SHIPS intensity guidance indicates
that SSTs will be cooling to 22C and less by 24 h, after which the
atmosphere is forecast to become too stable to produce convection.
As a result, Nicole is expected to become an extratropical low
by 36 hours. However, the intensity forecast shows only slight
weakening during the next 48 h due to the system receiving a shot of
baroclinic energy from the aforementioned shortwave trough. By 96 h,
if not sooner, Nicole is expected to be absorbed by a larger
extratropical low near the east coast of Greenland. Guidance from
the NOAA OPC was used for the forecast wind radii at 48 h and 72 h.

The primary hazard associated with Nicole will be high seas.  Recent
wave-height altimeter data indicate that a large area of 20-ft seas
exist near the hurricane.  In addition, swells from Nicole are
spreading far from the system, and High Seas Forecasts from OPC
and TAFB indicate that long-period swells will continue to radiate
outward and affect much of the North Atlantic basin during the next
few days.

FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 39.7N  45.6W   70 KT  80 MPH
 12H  17/0600Z 40.5N  44.5W   65 KT  75 MPH
 24H  17/1800Z 42.6N  42.5W   65 KT  75 MPH
 36H  18/0600Z 46.3N  39.6W   65 KT  75 MPH...POST-TROP/EXTRATROP
 48H  18/1800Z 51.3N  37.3W   65 KT  75 MPH...POST-TROP/EXTRATROP
 72H  19/1800Z 59.6N  32.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  20/1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW

$$
Forecaster Stewart
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