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Hurricane FLORENCE


Hurricane Florence Discussion Number  42
NWS National Hurricane Center Miami FL       AL062018
500 PM AST Sun Sep 09 2018

The last reconnaissance fix indicated that the pressure had fallen
to about 978 mb with Florence, a drop of about 6 mb in 4 hours, with
uncontaminated SFMR winds of about 70 kt. Since then, the satellite
presentation has continued to improve, with intensifying deep
convection near the center.  Thus the wind speed is set to 75 kt on
this advisory.

Radar data from the NOAA Hurricane Hunter indicated that there were
still a few breaks in the eyewall, possibly allowing some dry air to
mix into the core.  This structure has potentially kept Florence
from intensifying rapidly so far.  It is likely, however, that the
eyewall will close soon with low environmental shear present,
resulting in a faster intensification rate.  The guidance is
remarkably well clustered, with all of the hurricane models showing
category 4 strength within 48 hours, which is uncommon given the
current intensity.  The new forecast continues to show rapid
intensification and is increased 5 or 10 kt at most time periods,
but it is still not as high as the Florida State Superensemble or
the NOAA corrected consensus models.  It is worth noting that the
model guidance is also significantly increasing the size of
Florence's wind field over the next few days, and the official
forecast reflects this trend.

The fixes from the aircraft indicate that Florence hasn't gained
much latitude yet, and continues moving westward at about 6 kt.
There is no change to the synoptic reason as a very strong ridge is
forecast to build over the northwestern Atlantic during the next few
days.  This pattern should steer Florence west-northwestward at a
much faster forward speed by Tuesday.  On Wednesday, the hurricane
will likely turn northwestward and slow down somewhat due to another
ridge forming over the Ohio Valley.   The most notable change from
the previous advisory is that most of the models are showing a
faster motion in 3 or 4 days, which unfortunately increases the risk
of a destructive hurricane landfall.  The GFS and its ensemble mean
are outliers from the main model envelope, showing the system near
the Outer Banks, while the rest of the guidance is well to the
southwest. While a near-miss isn't impossible given the spread of
the ECMWF Ensemble, there is much more support for a track to the
southwest, especially considering the poleward bias of the GFS thus
far this season. Therefore, the official track forecast is shifted a
little bit to the southwest, and is very close to the
corrected-consensus models.

The NOAA G-IV jet is conducting a synoptic surveillance mission this
afternoon to gather data near and around Florence for assimilation
into the numerical models, and these missions will continue through
Tuesday. In addition, upper-air stations across portions of the
central and eastern U.S. are conducting special 0600 UTC and 1800
UTC radiosonde launches to collect extra data for the numerical
models. Hopefully these data will help improve the track and
intensity forecasts.

Key Messages:

1. There is an increasing risk of two life-threatening impacts from
Florence: storm surge at the coast and freshwater flooding from a
prolonged heavy rainfall event inland. While it is too soon to
determine the exact timing, location, and magnitude of these
impacts, interests at the coast and inland from South Carolina into
the mid-Atlantic region should closely monitor the progress of
Florence, ensure they have their hurricane plan in place, and follow
any advice given by local officials.

2. Large swells affecting Bermuda and portions of the U.S. East
Coast will continue this week.  These swells will result in
life-threatening surf and rip currents.


INIT  09/2100Z 24.4N  57.0W   75 KT  85 MPH
 12H  10/0600Z 24.6N  58.3W   90 KT 105 MPH
 24H  10/1800Z 25.1N  60.4W  105 KT 120 MPH
 36H  11/0600Z 25.9N  63.1W  115 KT 130 MPH
 48H  11/1800Z 27.0N  66.2W  125 KT 145 MPH
 72H  12/1800Z 30.3N  72.6W  130 KT 150 MPH
 96H  13/1800Z 33.5N  77.5W  120 KT 140 MPH
120H  14/1800Z 35.0N  79.0W   60 KT  70 MPH...INLAND

Forecaster Blake