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Subtropical Storm ANA Forecast Discussion Number 2
2015-05-08 10:56:17| National Hurricane Center (Atlantic)
Issued at 500 AM EDT FRI MAY 08 2015 000 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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