Atlantic Subtropical Storm ANA Discussion Number 4

000

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

http://www.nhc.noaa.gov/text/MIATCDAT1.shtml