[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 170848
TCDAT1

Tropical Storm Arthur Discussion Number   3
NWS National Hurricane Center Miami FL       AL012020
500 AM EDT Sun May 17 2020

Arthur has not changed much in organization overnight.  The storm
features a large curved convective band over the eastern semicircle
of the circulation, and the low-level center appears to be exposed
to the west of that band.  The intensity is held at 35 kt in
agreement with a subjective Dvorak estimate from TAFB and ADT
estimates from UW-CIMSS.  An Air Force Hurricane Hunter aircraft is
scheduled to investigate the cyclone around 12Z which should provide
a good estimate of Arthur's intensity.

Although Arthur will be crossing back over the Gulf Stream tonight
and Monday, vertical shear is forecast to steadily increase during
that time.  With these counteracting influences on intensity
change, only slight strengthening is anticipated during the next
24-36 hours.  The official forecast is close to the model consensus
and is similar to the previous one. In 2-3 days, some strengthening
due to baroclinic processes is possible, since the global models
depict extratropical transition around that time.  Later in
the forecast period, the dynamical guidance shows weakening as the
frontal gradients decrease.

The storm has been moving a little to the left of the previous
estimates and the motion is now around 015/8 kt.  An approaching
mid-level trough over the eastern U.S. should cause the cyclone to
accelerate northeastward during the next 48 hours or so.  Later in
the forecast period, Arthur or its post-tropical remnants should
turn eastward within a general westerly flow field.  There has been
a bit of a westward shift in much of the track guidance for the
next 1-2 days, which has necessitated a leftward adjustment of the
official forecast track.  Since the new NHC forecast is now closer
to the North Carolina Outer Banks, the Tropical Storm Watch has
been changed to a Tropical Storm Warning for that area.

Key Messages:

1. A Tropical Storm Warning is now in effect for a portion of the
North Carolina coast.  Tropical-storm-force winds and heavy rains
are expected there on Monday.

2. Dangerous coastal surf conditions and rip currents are expected
to spread northward from Florida to the mid-Atlantic states during
the next few days.  See products from your local National Weather
Service Forecast Office for more details.

FORECAST POSITIONS AND MAX WINDS

INIT  17/0900Z 30.0N  77.6W   35 KT  40 MPH
 12H  17/1800Z 31.2N  77.2W   40 KT  45 MPH
 24H  18/0600Z 33.2N  76.4W   45 KT  50 MPH
 36H  18/1800Z 35.5N  74.7W   45 KT  50 MPH
 48H  19/0600Z 36.9N  72.0W   50 KT  60 MPH
 60H  19/1800Z 37.3N  69.4W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  20/0600Z 37.0N  67.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  21/0600Z 36.0N  66.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  22/0600Z...DISSIPATED

$$
Forecaster Pasch
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