[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 182032
TCDAT1

TROPICAL DEPRESSION JULIA DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112016
500 PM EDT SUN SEP 18 2016

Julia's low-level circulation has continued to improve despite the
lack of organized deep convection near the well-defined center.
However, some tight curved banding features consisting of shallow to
moderate convection have developed within 100 nmi of the center
during the past few hours, a hint that the mid-level moisture is
beginning to increase. The initial intensity remains 25 kt based on
on a TAFB intensity estimate of T1.5/25 kt, and a 1535Z ASCAT pass
that showed some surface winds near 25 kt just north of the center.

Julia is moving northwestward or 330/06 kt. The cyclone is forecast
to slow down and gradually turn toward the north-northwest and north
later tonight. A northward motion is then expected to persist, ahead
of a strong shortwave trough that is forecast to move toward the
western Carolinas, until Julia moves near or just onshore the the
southeastern coast of North Carolina on Tuesday. After that time,
it is uncertain whether or not a weakening Julia will lift out to
the northeast and merge with a frontal boundary, or drift
southwestward as a remnant low. Regardless of the status of Julia by
72 hours, the models are in good agreement that the system will not
be a tropical cyclone at that time or thereafter due to strong
vertical wind shear and land interaction. The official track
forecast is similar to the previous advisory, which is a compromise
of the various global and regional model solutions.

Julia has a narrow window of opportunity to strengthen tonight and
Monday morning when the vertical wind shear is forecast to weaken
significantly and the upper-level flow is expected to become more
anticyclonic. These more conducive dynamics are forecast to coincide
with the nighttime convective maximum period and also during the
time when Julia will be over the Gulf Stream where SSTs are 29-30C.
Buoy reports offshore the South Carolina coast indicate that surface
dew points have increased to near 80F, a further indication that the
atmosphere surrounding Julia is becoming more conducive for
regeneration of convection near the center later tonight. By Monday
afternoon and evening, increasing southwesterly shear ahead of the
aforementioned shortwave trough should induce steady weakening,
which is expected to continue as the cyclone approaches the coast
of North Carolina. The intensity forecast remains unchanged is a
little below the consensus model IVCN. However, due to the
possibility that Julia could be a little stronger than currently
expected, an Air Force Reserve Hurricane Hunter aircraft has
tentatively been tasked to investigate the cyclone Monday afternoon.

The primary threat from Julia will be locally heavy rainfall from
eastern North Carolina northward to the Mid-Atlantic states and
the northeastern U.S. when moisture from the cyclone, or its
remnants, will interact with an approaching frontal system.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 32.3N  78.0W   25 KT  30 MPH
 12H  19/0600Z 33.0N  78.0W   25 KT  30 MPH
 24H  19/1800Z 34.0N  77.7W   30 KT  35 MPH
 36H  20/0600Z 34.6N  77.5W   30 KT  35 MPH...INLAND
 48H  20/1800Z 34.9N  77.5W   25 KT  30 MPH...INLAND
 72H  21/1800Z 34.2N  78.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  22/1800Z...DISSIPATED

$$
Forecaster Stewart

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