[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 090341
TCDAT1

SUBTROPICAL STORM ANA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012015
1100 PM EDT FRI MAY 08 2015

Data from an Air Force Reserve Unit Hurricane Hunter aircraft
indicate that Ana has intensified.  The strongest winds were
measured in a band well to the east and northeast of the center.
The current intensity is set at 50 kt, a little below the highest
SFMR winds which are believed to be slightly rain-inflated.
The satellite presentation of Ana is still somewhat subtropical,
with almost all of the deep convection in a band over the northern
semicircle of the circulation.  Moreover, observations from the
Hurricane Hunters indicate a radius of maximum winds of no less
than 50-60 n mi.  Therefore Ana is still being designated as a
subtropical cyclone at this time.  However, there is some indication
that deep convection is beginning to develop nearer to the center,
and this is a sign that the transition to a tropical cyclone may
occur not long from now.

Center fixes from the aircraft show a general northward drift of
350/2.  There is little change to the track forecast reasoning from
the previous package.  Over the next few days, the presistent
blocking ridge to the north of Ana is forecast to break down and
shift eastward as a broad mid-tropospheric trough moves into
the U.S. Ohio Valley region.  This evolution of the steering flow
should cause Ana to turn northwestward and then northward at a
slightly faster forward speed before crossing the coast in 36 to 48
hours. Beyond that time, the flow ahead of the trough should carry
Ana or its remnants northeastward at a substantially faster forward
speed. The official track forecast is close to the previous one and
also close to the latest multi-model consensus.

Dynamical and statistical/dynamical intensity model guidance do not
show much additional strengthening.  In 24 hours or so, as Ana
moves northwest of the Gulf Stream, it should encounter
progressively cooler waters.  This, along with the entrainment of
drier air, should lead to weakening.  The official wind speed
forecast is fairly similar to the intensity model consensus.  By 96
hours, the latest global model runs show the system degenerating
into an open trough as Ana's post-tropical remnants merge with a
large extratropical low over Atlantic Canada.

FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 32.1N  77.4W   50 KT  60 MPH
 12H  09/1200Z 32.4N  77.6W   50 KT  60 MPH
 24H  10/0000Z 32.9N  78.1W   45 KT  50 MPH
 36H  10/1200Z 33.6N  78.7W   40 KT  45 MPH
 48H  11/0000Z 34.3N  78.6W   35 KT  40 MPH...INLAND
 72H  12/0000Z 37.0N  76.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 96H  13/0000Z...DISSIPATED

$$
Forecaster Pasch
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