[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 081459
TCDAT1

SUBTROPICAL STORM ANA DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012015
1100 AM EDT FRI MAY 08 2015

Satellite images indicate that Ana is starting to show signs of
transforming into a tropical storm, with a more compact structure
and tighter convective bands near the center.  In addition,
aircraft reconnaissance data indicate that the maximum wind band is
becoming sharper and migrating inward.  The storm still has
less-intense convection than most tropical cyclones, however, and is
still co-located with an upper-level low; consequently Ana remains
best classified as subtropical for now. The maximum winds are
estimated to be 40 kt based on the SFMR and flight-level
data.

Ana has been meandering for the past several hours under a blocking
ridge along the U.S. east coast, although recently the storm has
drifted eastward toward a convective burst.  This ridge will
slowly move eastward over the next couple of days, which
should steer the storm generally slowly northwestward.  Model
guidance is in good agreement in bringing Ana to the coast of the
Carolinas in about two days.  After that, a strong trough should
cause Ana to move more quickly to the north and east late Sunday
and into early next week. No significant changes were required to
the previous forecast track, which remains close to the model
consensus. Extratropical transition is anticipated in about four
days - in line with the global model guidance.

Some strengthening of Ana is possible since the cyclone is embedded
within an environment of cold upper-level temperatures, leading to
more thunderstorms than one would expect over the marginally warm
waters.  However, there is quite a bit of dry air around the storm,
which could help limit convection.  Most of the guidance shows some
intensification during the next day or so, and the official forecast
does the same. As Ana approaches the coast, some weakening seems
probable due to the storm moving over cooler shelf waters. The
latest NHC forecast is close to the previous one, although a little
higher at 36 and 48 hr to reflect the latest guidance.


FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 31.5N  77.3W   40 KT  45 MPH
 12H  09/0000Z 31.8N  77.5W   45 KT  50 MPH
 24H  09/1200Z 32.1N  77.8W   45 KT  50 MPH
 36H  10/0000Z 32.6N  78.3W   45 KT  50 MPH
 48H  10/1200Z 33.2N  78.9W   40 KT  45 MPH
 72H  11/1200Z 35.1N  78.2W   30 KT  35 MPH...INLAND
 96H  12/1200Z 39.0N  72.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
120H  13/1200Z 44.5N  57.0W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake
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