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Tropical Storm ANA Forecast Discussion Number 10
2015-05-10 11:00:33| National Hurricane Center (Atlantic)
Issued at 500 AM EDT SUN MAY 10 2015 000 WTNT41 KNHC 100900 TCDAT1 TROPICAL STORM ANA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL012015 500 AM EDT SUN MAY 10 2015 Satellite and radar data indicate that Ana's convective structure and organization have continued to increase since the previous advisory. Doppler radar data out of Wilmington, North Carolina (KLTX) indicate average velocities of around 60 kt just a few thousand a feet above the offshore waters, which would normally equate to 45-50 kt winds at the surface. However, observations from buoys, ships, and coastal surface stations indicate that the typically downward mixing of these stronger winds is not occurring due to the cooler shelf waters stabilizing the boundary layer. The initial intensity of 40 kt, which could be generous, is based on an earlier report of a 41-kt wind from Buoy 41013 during passage of a heavy rain band. Doppler radar data continue to indicate that Ana has been moving slowly north-northwestward at about 330/04 kt since the previous advisory. The cyclone should maintain this general motion this morning, and gradually turn more northward by this afternoon and evening. On Monday, an approaching large, deep-layer trough should turn Ana northeastward, accompanied by a marked increase in forward speed of about 12-15 kt. The NHC track forecast is essentially just an update of the previous advisory track and lies close to the TVCN consensus model. Cold shelf waters of 20-21C have taken their toll on Ana's surface wind field even though the convective banding has improved. Rapid weakening of the inner-core wind field should occur after the center of Ana moves inland. However, some strong rain bands accompanied by tropical-storm-force winds are expected to persist near and just offshore the North Carolina coast today, and that is the reason for keeping the system as a tropical storm for the next 12 hours or so. After that, slow weakening below tropical storm status is expected, although there could be gusts to tropical-storm-force in some of the heavier rain squalls over water. Ana is forecast to become a post-tropical low on Monday, and be absorbed by a larger extratropical low by Tuesday when the cyclone is near or east of the DelMarVa peninsula. The intensity forecast closely follows the Decay-SHIPS model. Since Ana is moving onshore, the reconnaissance flight originally scheduled for this morning has been canceled. Special thanks for the Air Force Reserve Hurricane Hunters for their flights into Ana owing to their limited resources during the pre-hurricane season. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 33.8N 78.7W 40 KT 45 MPH 12H 10/1800Z 34.4N 78.7W 35 KT 40 MPH...INLAND 24H 11/0600Z 35.6N 77.9W 30 KT 35 MPH...INLAND 36H 11/1800Z 37.4N 76.3W 30 KT 35 MPH...INLAND 48H 12/0600Z 39.7N 73.4W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 13/0600Z...ABSORBED $$ Forecaster Stewart
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