[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 080856
TCDAT1

SUBTROPICAL STORM ANA DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012015
500 AM EDT FRI MAY 08 2015

Subtropical Storm Ana has remained convectively challenged
overnight with only a small cluster of thunderstorms noted revolving
through the southern semicircle, and only shallow isolated
convection having recently developed in the inner-core region. The
initial intensity remains at 40 kt based on previous recon data and
the lack of any significant change in the overall convective
pattern since that flight.

The initial motion continues to be a slow drift to the northwest
or north-northwest at only 1-2 kt. Ana is embedded in a blocking
pattern that is expected to persist for the next 3 days or so until
a strong mid-tropospheric low/trough currently located over the
western U.S. moves into the central and southern Plains and nudges
Ana northward and eventually northeastward by early next week.
During the next 48 hours, Ana is expected to move toward the
southeastern U.S. at a very slow pace. The global and regional
models are in remarkably good agreement on this weak steering
pattern persisting through the weekend so, the official forecast
track is essentially just an update of the previous advisory track
and lies close to the consensus model TVCA.

Water vapor imagery indicates that a tight mid-/upper-level low has
finally become juxtaposed with the surface low, and the two have
remained nearly stationary over the relatively warm waters of the
Gulf Stream. However, intrusions of dry air into the inner core have
been noted in satellite imagery and upper-air data during the
past several hours, which have likely been the main reason for the
lack of deep convection developing near the center. But with the
lows now vertically stacked and expected to remain over SSTs of
at least 25C for the next 24 hours, some slight strengthening is
expected. Ana could also transition to a tropical storm during
that time. By 48 hours and beyond, however, Ana's slow movement will
take the cyclone over colder shelf waters of around 20C-22C, and
weakening is expected due to the air in the inner core becoming more
stable. Most of the global models now show Ana remaining a distinct
entity through the forecast period and accompanied by winds near
gale force. As a result, the forecast calls for Ana to remain an
extratropical low on Days 4 and 5. The official intensity forecast
is similar to the previous advisory and the Decay-SHIPS model.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 31.6N  77.8W   40 KT  45 MPH
 12H  08/1800Z 31.7N  77.8W   45 KT  50 MPH
 24H  09/0600Z 31.9N  78.0W   45 KT  50 MPH
 36H  09/1800Z 32.2N  78.2W   40 KT  45 MPH
 48H  10/0600Z 32.8N  78.9W   35 KT  40 MPH
 72H  11/0600Z 34.1N  79.3W   30 KT  35 MPH...INLAND
 96H  12/0600Z 37.7N  75.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  13/0600Z 43.0N  65.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart
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