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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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