[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 080858
TCDAT4

Tropical Storm Michael Discussion Number   7
NWS National Hurricane Center Miami FL       AL142018
400 AM CDT Mon Oct 08 2018

Michael has become better organized this morning, with the deep
convection migrating westward on top of the low-level center and
upper-level outflow beginning to increase within the western
semicircle.  An Air Force Reserve Hurricane Hunter aircraft made
several passes through the system during the past few hours, and
somewhat surprisingly, found that the central pressure has fallen
to about 983 mb and maximum winds have increased to near 60 kt.
This increase in intensity indicates that despite the shear which
has been affecting Michael, the system has, by definition, rapidly
intensified during the past 24 hours.

With the increase in the initial wind speeds, the official
intensity forecast is higher than in the previous forecast.
Decreasing vertical shear and very warm sea surface temperatures
are expected to support continued strengthening, and due to the
favorable conditions, the NHC intensity forecast follows a blend of
the IVCN consensus and the HCCA model.  This new official forecast
brings the intensity to just below major hurricane strength in 48
hours, and since the storm will still be over water for a time
between 48 and 72 hours, there is a real possibility that Michael
will strengthen to a major hurricane before landfall.  Weakening is
expected after landfall, but the system will likely maintain
tropical storm strength after day 4 when it moves off the east
coast of the United States.  Michael should then become an
extratropical low by day 5.

The reconnaissance fixes indicate that Michael's center is moving
northward, or 360 degrees at 6 kt.  A general northward motion with
some increase in forward speed is expected during the next 48 hours
as Michael enters the southerly flow between high pressure over the
western Atlantic and a deep-layer trough over the western and
central United States.  After 48 hours, Michael is expected to turn
northeastward toward and across the southeastern United States,
exiting over the western Atlantic between days 4 and 5.  Nearly all
of the track models have shifted westward after 24 hours, which
left the previous forecast near the eastern edge of the guidance
envelope.  Due to this shift, the new NHC track forecast has also
been adjusted westward close to the consensus aids.  Overall the
track guidance is in fairly good agreement up until landfall along
the Florida Panhandle or Florida Big Bend, which has yielded a
fairly confident track forecast.


Key Messages:

1. Hurricane conditions are expected over portions of western Cuba,
where a hurricane warning is now in effect.  Tropical storm
conditions are expected over the northeastern Yucatan Peninsula and
the Isle of Youth today.

2.  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.

3.  Michael is forecast to be a hurricane, and possibly a major
hurricane, when it reaches the northeastern Gulf Coast by mid-week,
and storm surge and hurricane watches are now in effect for
portions of the area.  Some areas along the Florida Gulf Coast are
especially vulnerable to storm surge, regardless of the storm's
exact track or intensity.  Residents in the watch areas should
monitor the progress of this system and follow any advice given by
local officials.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 20.6N  85.5W   60 KT  70 MPH
 12H  08/1800Z 21.7N  85.6W   70 KT  80 MPH
 24H  09/0600Z 23.5N  86.1W   85 KT 100 MPH
 36H  09/1800Z 25.2N  86.7W   90 KT 105 MPH
 48H  10/0600Z 27.2N  86.7W   95 KT 110 MPH
 72H  11/0600Z 31.2N  84.5W   55 KT  65 MPH...INLAND
 96H  12/0600Z 35.5N  77.5W   50 KT  60 MPH...INLAND
120H  13/0600Z 40.5N  64.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg
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