[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 020857
TCDAT1

TROPICAL STORM ARTHUR DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012014
500 AM EDT WED JUL 02 2014

Despite a somewhat ragged appearance on satellite imagery, Arthur
has strengthened overnight. Data from two ASCAT passes between 02
and 03 UTC showed a broad area of 45-50 kt winds east and northeast
of the center. In addition, NOAA and Air Force Reserve Hurricane
Hunter aircraft have found surface winds in the 45-50 kt range to
the south and northeast of the center, while also finding the
central pressure has fallen to about 996 mb. Based on all of
these data, the initial intensity is set to 50 kt.

Arthur is still suffering the effects of dry air aloft being
entrained into the western half of the circulation, which
features only limited cold cloud tops. The primary convective band
is situated east and southeast of the center, and some semblance of
an eye has been visible in satellite and radar imagery and was
reported by the aircraft. This lopsided structure suggests that
Arthur will not strengthen quickly in the short term. However, given
an otherwise favorable environment of warm water and weak wind
shear, all of the intensity guidance shows the cyclone becoming a
hurricane in 24 to 36 hours, and so does the official forecast. By
72 hours, Arthur will be moving into a high shear environment ahead
of an advancing mid/upper-level trough, which should result in
weakening during the extratropical transition process.  The NHC
intensity forecast is close to the intensity consensus aid IVCN
through the period.

Arthur has begun moving steadily northward at around 5 kt. The
overall track forecast reasoning remains unchanged, as the tropical
cyclone should continue northward for the next 12 to 24 hours
and then gradually accelerate northeastward between the
aforementioned trough and a strengthening ridge to the east. The
track guidance envelope has shifted back to the west a little for
this cycle, and the NHC forecast has been adjusted in that
direction, but now lies on the eastern edge of the guidance
envelope through 48 hours.

Given the new NHC forecast, hurricane and tropical storm watches
have been issued for portions of the coasts of South and North
Carolina. Warnings may be required for portions of these areas
later today.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 28.4N  79.1W   50 KT  60 MPH
 12H  02/1800Z 29.3N  79.3W   55 KT  65 MPH
 24H  03/0600Z 30.5N  79.1W   60 KT  70 MPH
 36H  03/1800Z 32.1N  78.1W   70 KT  80 MPH
 48H  04/0600Z 34.2N  76.0W   75 KT  85 MPH
 72H  05/0600Z 40.0N  69.0W   75 KT  85 MPH
 96H  06/0600Z 46.0N  62.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  07/0600Z 50.0N  55.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brennan


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