[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 082051
TCDAT1

SUBTROPICAL STORM ANA DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL012015
500 PM EDT FRI MAY 08 2015

Ana is in the latter stages of tropical transition with curved deep
convection closer to the center, with some evidence of a shrinking
radius of maximum winds.  Still, the convection isn't particularly
deep, and an upper-level low remains basically on top of the
cyclone.  Ana will remain a subtropical cyclone on this advisory,
but it would not be surprising if the aircraft mission this evening
found enough tropical characteristics to signal a transition to
a tropical storm.  The maximum winds are kept at 40 kt, which is a
blend of the satellite classifications from TAFB and SAB.

Ana continues to meander beneath a blocking ridge along the U.S.
east coast.  While the overall ridge pattern shifts slowly eastward,
the western part of the ridge is forecast to build slightly over the
Ohio Valley tomorrow.  This will help steer Ana more to the
northwest, and model guidance continues to be in good agreement in
bringing Ana to the coast of the Carolinas in about two days.  Only
a small eastward adjustment was required to the previous forecast
track near the time of landfall.  A strong trough should then cause
Ana to move more quickly to the north and east late Sunday and into
early next week.   Extratropical transition should be complete by 96
hr due to interaction of Ana with the trough and the cold waters of
the North Atlantic.

Some intensification of Ana is still possible since the cyclone
remains parked over the Gulf Stream with cold upper-level
temperatures promoting more convection than one would expect given
the marginally warm waters.  However, there is quite a bit of dry
air around the storm, which seems to be limiting convection. Some
weakening of Ana seems probable on Sunday due to the storm's motion
over cooler shelf waters. The latest NHC forecast is close to
the previous one, near or slightly above the model consensus. Most
of the global models show a little bit of strengthening of Ana in
its extratropical phase, so the intensity was raised at 96 and 120
hr.



FORECAST POSITIONS AND MAX WINDS

INIT  08/2100Z 31.7N  77.4W   40 KT  45 MPH
 12H  09/0600Z 31.9N  77.6W   45 KT  50 MPH
 24H  09/1800Z 32.3N  77.9W   45 KT  50 MPH
 36H  10/0600Z 33.0N  78.4W   40 KT  45 MPH
 48H  10/1800Z 33.6N  78.7W   35 KT  40 MPH
 72H  11/1800Z 36.0N  77.0W   30 KT  35 MPH...INLAND
 96H  12/1800Z 40.5N  69.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  13/1800Z 46.0N  50.0W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake
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