[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 180258
TCDAT5

TROPICAL STORM NICOLE DISCUSSION NUMBER  56
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152016
1100 PM AST MON OCT 17 2016

The old adage about tropical cyclones transitioning to extratropical
once the latitude is larger than the longitude does not apply to
Nicole.  The system has been able to maintain a coherent inner core
of deep convection, which wraps about two-thirds the way around its
center.  This is, however, somewhat reduced from earlier today and
the Dvorak data-t numbers from TAFB and SAB have dropped. A just
arriving ASCAT-A scatterometer pass from 0019Z indicates that peak
winds are about 60 kt and this may be a bit generous. Thus Nicole
has weakened to a tropical storm.

Nicole's resilience as a tropical cyclone is likely due to it being
embedded within very low vertical shear and in quite cold upper
tropospheric temperatures, despite the SSTs dropping to near 20 deg
C.  However, Nicole should soon transition to an extratropical
cyclone, as frontal boundaries develop near the center of the system
by tomorrow.  Even though it will become extratropical, it is
anticipated that Nicole will remain a large and powerful system for
the next couple of days before being absorbed by a separate
extratropical cyclone in about three days. The intensity forecast is
slightly less than that from the previous advisory because of the
lowered initial intensity and is based upon a deterministic global
model consensus.

Nicole is moving toward the northeast at about 22 kt, as it is being
advected along in the deep layer southwesterly flow ahead of a
shortwave trough over eastern Canada.  A 2019Z AMSU pass and the
ASCAT-A scatterometer pass indicated that the surface center is
somewhat west of where the center appears to be from the infrared
imagery.  Nicole should accelerate and turn toward the north by
tomorrow.  This track forecast is similar to that from the previous
advisory and is based upon a blend of the deterministic and ensemble
global models.

The main hazard associated with Nicole will continue to be the large
area of high seas.  Swells from Nicole will affect much of the North
Atlantic basin during the next couple of days.

The post-tropical portion of the forecast is based on guidance from
the NOAA Ocean Prediction Center.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 44.8N  41.0W   60 KT  70 MPH
 12H  18/1200Z 48.3N  37.9W   60 KT  70 MPH...POST-TROP/EXTRATROP
 24H  19/0000Z 54.5N  36.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  19/1200Z 59.0N  34.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
 48H  20/0000Z 65.0N  33.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  21/0000Z...ABSORBED BY A LARGER EXTRATROPICAL LOW

$$
Forecaster Landsea

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