[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 012053
TCDAT1

TROPICAL STORM ARTHUR DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012014
500 PM EDT TUE JUL 01 2014

Although radar and satellite imagery indicate that the convective
pattern of Arthur has changed little since the previous advisory...
an Air Force Reserve reconnaissance aircraft investigating the
cyclone this afternoon has found that flight-level and SFMR surface
winds in the southeastern quadrant that support increasing the
intensity to 45 kt. In fact, the flight crew has been been bounced
around pretty good by strong thunderstorms in that area and have
been forced to climb to a higher altitude in order to avoid
significant turbulence.

Arthur has been drifting northwestward at 325/02 kt. No significant
change has been made to the previous forecast track or reasoning.
The latest reliable numerical models remain in good agreement on
large mid-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 to steadily increase
the southwesterly steering flow over the southeastern United States
and the extreme western Atlantic. By Days 4 and 5, Arthur is
forecast to accelerate rapidly northeastward ahead of the
aforementioned trough as an extratropical cyclone. The official
forecast track is again just an update of the previous advisory
track, and remains in the middle of the tightly packed guidance
envelope and close to the consensus model TVCA.

Northwesterly vertical wind shear is expected to gradually abate
over the next 48 hours, allowing Arthur to develop an upper-level
outflow pattern that is conducive to strengthening. The primary
inhibiting factor will be the occasional intrusions of dry mid-level
air to the north of the cyclone penetrating into the center and
briefly disrupting the inner-core convection. However, the global
and regional models are forecasting the inner core region to
moisten significantly by 36-48 hours, which should allow Arthur to
strengthen into a hurricane while the cyclone is over warm SSTs and
in light shear conditions. After 72 hours, Arthur will be be moving
over cooler water and is forecast to experience vertical wind shear
in excess of 30 kt, which should induce at least steady weakening.
The NHC intensity forecast closely follows the consensus model IVCN.

FORECAST POSITIONS AND MAX WINDS

INIT  01/2100Z 27.8N  79.4W   45 KT  50 MPH
 12H  02/0600Z 28.3N  79.4W   50 KT  60 MPH
 24H  02/1800Z 29.2N  79.5W   55 KT  65 MPH
 36H  03/0600Z 30.4N  79.2W   60 KT  70 MPH
 48H  03/1800Z 32.1N  78.3W   70 KT  80 MPH
 72H  04/1800Z 36.6N  73.6W   80 KT  90 MPH
 96H  05/1800Z 42.2N  65.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  06/1800Z 46.8N  57.5W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart



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