11 AM NHC Discussion:
The satellite and radar presentations of Florence have improved
somewhat this morning, with a 20-25 nmi wide eye closing off in the
radar data from the Morehead City and Wilmington WSR-88D Doppler
weather radars. However, an Air Force Reserve reconnaissance
aircraft investigating the hurricane this morning has not yet found
any flight-level or SFMR winds to support more than about 80 kt at
the surface thus far, even though the pressure has decreased to 955
mb. The initial intensity has only been lowered to 90 kt, given
that there are peak Doppler velocity values up to 110 kt with
average values of 95-97 kt at 15,000 ft in the northern eyewall
region, an area of the hurricane that the reconnaissance aircraft
has not yet sampled. The upper-level outflow pattern remains quite
impressive.
Florence has been gradually slowing down this morning, and the
initial motion estimate is now 315/09 kt. The subtropical ridge to
the northeast and east of Florence is now well-established between
Bermuda and the U.S. mid-Atlantic region and extends westward into
Virginia and the central Appalachians. This large-scale feature is
expected to keep the hurricane moving northwestward today, followed
by a turn toward the west at a much slower speed on Friday as the
ridge to the north of Florence weakens due to a weak shortwave
trough dropping slowly southward from the Ohio Valley. On days 3-5,
Florence is forecast turn toward the northwest and north around the
western periphery of the subtropical ridge, and move across western
South Carolina on Sunday, across western North Carolina and eastern
Tennessee on Monday, and then move up the spine of the Appalachians
as an extratropical low after the cyclone merges or interacts with a
frontal system. The new NHC forecast track is similar to the
previous one, and lies close to a blend of the consensus models
TVCA, HCCA, and FSSE.
Florence is currently approaching the Gulfstream current, and the
hurricane is forecast to move over warmer and deeper waters in 6-12
hours, which could allow for some slight strengthening. Just prior
to landfall in about 24 hours, Florence is expected to weaken some
due to upwelling of the shallow coastal waters. After landfall
occurs, rapid weaning of the stronger inner-core wind field is
expected to due land interaction and Florence's slow forward speed
of 5 kt or less. However, intense rainbands are expected to develop
over the Atlantic waters and keep moving along the coast and inland,
likely producing strong wind gusts through Saturday night.