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Hurricane MICHAEL


Hurricane Michael Discussion Number  10
NWS National Hurricane Center Miami FL       AL142018
1000 PM CDT Mon Oct 08 2018

Data from NOAA and Air Force Reserve hurricane hunter aircraft this
evening indicate that Michael has continued to strengthen...despite
westerly vertical shear of about 20 kt, which is most unusual. The
maximum 8000-ft flight-level winds measured by NOAA so far has
been 102 kt and maximum SFMR surface wind speed was 78 kt. The
central pressure measured by the two aircraft has been fluctuating
between 970 mb and 974 mb, which is likely due to small mesovortices
rotating around inside the fairly large 35-nmi-wide eye. Given the
aforementioned wind data and the possibility of locally enhanced
winds due to the mesovortices, the initial intensity has only been
increased to 80 kt rather than 85 kt, which the NOAA flight-level
wind data would typically support.

The initial motion estimate is 350/11 kt. The steering flow pattern
isn't forecast to change much, if at all, for the next 36-48 hours,
with Michael expected to remain caught between a deep-layer ridge
centered off of the U.S. east coast and a highly amplitude
mid-latitude trough over the U.S. Plains states and northern Mexico.
The combined deep-layer southerly flow should keep the hurricane
moving northward to north-northwestward for the next 36 hours or so.
Shortly thereafter and just prior to landfall, the approaching
mid-latitude trough is expected to turn Michael toward the
north-northeast or northeast.  By 48 hours and beyond, significant
acceleration toward the northeast ahead of the trough is forecast to
continue through the 120-h period, with Michael emerging off of the
U.S. mid-Atlantic coast around 96 hours. The new NHC forecast track
was nudged slightly to the east of the previous track through 36 h,
based on the more eastward initial position and a forward motion
that is still to the right or east of short term motion in the model
guidance, but is still near the consensus models TVCN, TVCX, and
NOAA-HCCA. By 48 hours and beyond, the official track is close to
the previous advisory track.

Michael's steady intensification over the past 48 hours in the face
of 20-kt westerly shear defies traditional logic. Either the shear
calculations are unrepresentative or Michael has become more
inertially stable due to its large eye and large outer wind field,
making it more shear resistant. Having said that, all of the model
guidance calls for the shear to decrease to around 10 kt or less by
36 hours, which argues for at least steady intensification during
that time given that Michael will be moving over warm SSTs of
28.5C-29C, which are about 1-2 deg C above average for this time of
the year. Less-than-normal weakening after landfall in the 48-
to 96-h period is expected due to Michael's fast forward speed of
20-30 kt. Re-strengthening as an extratropical low over water on
days 4 and 5 is forecast due to baroclinic interaction with a
frontal system and the cyclone being back over warm Atlantic waters.
The official intensity forecast is a little higher than the
consensus models IVCN and HCCA, and is similar to the previous
advisory and the FSSE model.

It should be noted that the location and magnitude of peak storm
surge flooding is very sensitive to small changes in the track,
intensity, and structure of the hurricane. Since there is still
uncertainty in all of these parameters, the official NHC storm surge
forecast and watch/warning areas includes various plausible
scenarios. Regardless of the eventual track and intensity of
Michael, life-threatening storm surge inundation is expected along
portions of the Florida Panhandle and Big Bend/Nature Coast, and the
storm surge watch has been upgraded to a storm surge warning for
parts of this area.

The NOAA G-IV aircraft is currently conducting a synoptic
surveillance mission over the Gulf of Mexico and dropsondes from
that mission will be assimilated into the 0000 UTC numerical models

Key Messages:

1. Life-threatening storm surge is likely along portions of the
coasts of the Florida Panhandle, Big Bend, and Nature Coast, and a
storm surge warning is in effect for these areas. Residents in these
areas should follow all advice given by their local officials.

2. A hurricane warning has been issued for portions of the Florida
Gulf Coast, and everyone in these areas should prepare for
life-threatening winds associated with the core of Michael.
Damaging winds will also extend inland across portions of the
Florida Panhandle, southern Georgia, and southeast Alabama as
Michael moves inland.

3. Heavy rainfall from Michael could produce life-threatening flash
flooding from the Florida Panhandle and Big Bend region into
portions of Georgia and South Carolina.

4. Hurricane conditions will continue in portions of western Cuba
through this evening, where a hurricane warning is in effect.

5. Michael is expected to produce heavy rainfall and flash flooding
over portions of western Cuba and the northeastern Yucatan Peninsula
of Mexico during the next couple of days.


INIT  09/0300Z 23.2N  85.3W   80 KT  90 MPH
 12H  09/1200Z 24.7N  85.9W   90 KT 105 MPH
 24H  10/0000Z 26.8N  86.3W  100 KT 115 MPH
 36H  10/1200Z 29.1N  85.9W  105 KT 120 MPH
 48H  11/0000Z 31.4N  84.4W   55 KT  65 MPH...INLAND
 72H  12/0000Z 35.9N  77.3W   45 KT  50 MPH...INLAND
 96H  13/0000Z 41.5N  63.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  14/0000Z 47.8N  46.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

Forecaster Stewart