Tuesday, July 01, 2014

Tropical Storm Arthur a potential long range threat to the region

WTNT41 KNHC 020252

1100 PM EDT TUE JUL 01 2014

Data from the Melbourne WSR-88D radar indicates that Arthur has a
complex structure this evening.  A mid-level cyclonic circulation
accompanied by a possible eye feature is clearly evident near 27.8N
78.8W.  However, the motions of the light showers/low clouds seen in
the radar data suggest that the low-level center is about 25-30 n mi
west of the mid-level center. Air Force Reserve and NOAA Hurricane
Hunter aircraft are scheduled to investigate Arthur early Wednesday
morning to see if the center has re-formed to the east. Pending the
arrival of the aircraft, the initial intensity remains 45 kt.

The initial motion is a rather uncertain 360/2.  The track guidance
models remain in good agreement on a large mid/upper-level trough
digging southeastward into the northeastern and mid-Atlantic states
during the next 72 hours, while a subtropical ridge east of the
Carolinas gradually strengthens. The combination of these two
systems is expected steer Arthur generally northward for 24 hours or
so, followed by a turn toward the northeast and gradual
acceleration. The combination of the lack of motion over the past
6-12 hours and the slightly more eastward initial position have
resulted in some eastward shift of the track guidance envelope.  As
a result, the new forecast track is also shifted slightly to the
east from the previous forecast. The official forecast is near the
center of the track guidance envelope and remains close to the
various consensus models.

Arthur is expected to be in an environment of light northwesterly
vertical wind shear for the next 60-72 hours.  This should allow for
continued development.  However, satellite total precipitable water
data suggests that pockets of dry air remain near the cyclone, and
these could hinder development.  Given these competing factors, the
new intensity forecast is changed little from the previous forecast
and calls for Arthur to become a hurricane in about 36 hours and
reach its peak intensity in about 72 hours.  After that time, the
cyclone should undergo extratropical transition and weaken as it
merges with the mid/upper-level trough.

Based on the new forecast track, additional watches and warnings
are not necessary for the North Carolina and South Carolina coasts
at this time.  However, tropical storm or hurricane watches will
likely be required for portions of these areas on Wednesday.


INIT  02/0300Z 27.9N  79.2W   45 KT  50 MPH
12H  02/1200Z 28.6N  79.3W   50 KT  60 MPH
24H  03/0000Z 29.7N  79.2W   60 KT  70 MPH
36H  03/1200Z 31.0N  78.7W   65 KT  75 MPH
48H  04/0000Z 32.8N  77.3W   75 KT  85 MPH
72H  05/0000Z 37.5N  72.0W   80 KT  90 MPH
96H  06/0000Z 43.0N  64.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  07/0000Z 47.5N  57.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

Forecaster Beven


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