[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 041442
TCDAT1

HURRICANE ARTHUR DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012014
1100 AM EDT FRI JUL 04 2014

The eye of Arthur remains evident in geostationary satellite imagery
although the cloud tops surrounding the eye have warmed this
morning.  The U.S. Air Force Reserve Hurricane Hunter aircraft has
measured 94-kt 700 mb flight-level winds in the southeastern
quadrant, but it appears that these winds are not effectively mixing
down to the surface, as peak SFMR surface winds have been 68 kt.
Using a blend of the these data, the initial intensity has been
reduced to 80 kt.  Arthur will be moving over cooler water and the
shear will be significantly increasing through tonight, which should
cause gradual weakening. The hurricane will also interact with a
deep-layer trough and associated cold front that will be moving off
the United States east coast later today.  This should cause the
hurricane to complete transition into an extratropical cyclone in
about 24 hours.  After that time, continued weakening is expected
while the post-tropical cyclone moves over the North Atlantic.

Arthur is moving northeastward with an initial motion of 040/21 kt.
The hurricane should continue moving northeastward during the next
24 to 36 hours ahead of the aforementioned deep-layer trough. The
center of the cyclone is forecast to move over Nova Scotia on
Saturday and track models are in good agreement on this portion of
the forecast.  The track guidance become very divergent after 48
hours, with the ECMWF taking the cyclone northward and northwestward
while the GFS shows an east-northeastward motion near Newfoundland.
Out of continuity for the previous forecasts, the NHC track
continues to follow the eastward scenario shown by the GFS and GFS
ensemble mean, but it now shows a somewhat slower motion by day 5.
It is possible that this portion of the track will need to be
adjusted in future forecasts.

Hourly position updates and two-hourly intermediate advisories have
been discontinued.  Three-hourly intermediate advisories will
continue as long as coastal warnings remain in effect.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 37.7N  73.4W   80 KT  90 MPH
 12H  05/0000Z 40.2N  70.1W   75 KT  85 MPH
 24H  05/1200Z 44.0N  66.1W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  06/0000Z 46.1N  63.2W   55 KT  65 MPH...POST-TROP/EXTRATROP
 48H  06/1200Z 48.0N  59.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  07/1200Z 55.0N  52.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  08/1200Z 59.0N  46.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  09/1200Z 62.0N  35.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown



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