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Subtropical Storm ANA Forecast Discussion Number 4
2015-05-08 22:51:58| National Hurricane Center (Atlantic)
Issued at 500 PM EDT FRI MAY 08 2015 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
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