[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 080858
TCDAT4

HURRICANE MATTHEW DISCUSSION NUMBER  41
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142016
500 AM EDT SAT OCT 08 2016

Coastal Doppler weather radars this morning continue to depict a
40-nmi wide eye with a band of intense convection located in the
northwestern quadrant along the coasts of extreme eastern Georgia
and South Carolina from Tybee Island northeast to near the entrance
of Charleston Harbor. Air Force Reserve and NOAA reconnaissance wind
data, along with Doppler radar velocity data and surface
observations, indicate that hurricane-force wind gusts in excess of
80 kt are occuring along the aforementioned coastal areas. Based on
700-mb maximum flight-level winds of 108 kt, peak SFMR surface winds
of 83 kt, and Doppler velocities of 100-102 kt between 8000-11000
ft, the initial intensity will remain at 90 kt for this advisory.

The initial motion estimate is 015/10 kt. Matthew made a northward
jog since the previous advisory, but now appears to moving
north-northeastward based on the latest radar and recon fixes.
However, the more northward motion earlier has increased the
possibility that the center of Matthew's eye will move onshore the
coast of South Carolina later this morning or early afternoon as the
cyclone turns northeastward ahead of a strong shortwave trough.
Regardless of whether or not the center makes landfall,
hurricane-force winds in the northern eyewall will lash much of the
coast of South Carolina today as the center moves to a position just
east of Charleston Harbor in about 12 hours. After that, the models
are in fair agreement on Matthew turning eastward through 36 hours
as the cyclone briefly gets captured by the aforementioned shortwave
trough. However, by 48 hours and beyond, Matthew is expected to
turn southeastward and southward as the cyclone moves around the
eastern periphery of an amplifying ridge located east of Florida.
In the 48-72 hours time period, some erratic motion could occur as
Matthew and Tropical Storm Nicole briefly undergo some binary
interaction before separating by 96 hours. The official forecast
track closely follows a blend of the GFS and ECMWF solutions.

The vertical wind shear is forecast to increase to more than 30 kt
by 12 hours, which should induce steady weakening. At 48 hours and
beyond, the SHIPS model is forecasting the shear to increase to
more than 40 kt, resulting in rapid weakening to remnant low status
by 120 hours. However, the shear forecast appears to be overdone
since both the GFS and ECMWF models indicate that Matthew and Nicole
will both be moving underneath a narrow 200 mb ridge axis, which
should act to reduce the shear across the two cyclones in the 48-96
hour period. The official intensity forecast closely follows the
consensus model IVCN, and maintains Matthew as a tropical cyclone
throughout the forecast period.

KEY MESSAGES:

1.  The western eyewall of Matthew, which contains hurricane-force
winds, is now moving over the northern coast of Georgia and
the southern coast of South Carolina and should spread up the coast
during the day.

2.  Hurricane winds increase very rapidly with height, and occupants
of high-rise buildings along the coast are at particular risk of
strong winds.  Winds at the top of a 30-story building will average
one Saffir-Simpson category higher than the winds near the surface.

3.  The water hazards remain, even if the core of Matthew remains
offshore.  These include the danger of life-threatening inundation
from storm surge, as well as inland flooding from heavy rains from
Florida to North Carolina.

4.  The National Hurricane Center is issuing Potential Storm Surge
Flooding Maps, and Prototype Storm Surge Watch/Warning Graphics for
Matthew.  It is important to remember that the Potential Storm Surge
Flooding Map does not represent a forecast of expected inundation,
but rather depicts a reasonable worst-case scenario -- the amount of
inundation that has a 10 percent chance of being exceeded.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 32.0N  80.5W   90 KT 105 MPH
 12H  08/1800Z 32.9N  79.4W   80 KT  90 MPH
 24H  09/0600Z 33.7N  77.1W   70 KT  80 MPH
 36H  09/1800Z 33.4N  75.1W   60 KT  70 MPH
 48H  10/0600Z 32.6N  73.5W   50 KT  60 MPH
 72H  11/0600Z 29.0N  73.5W   40 KT  45 MPH
 96H  12/0600Z 26.0N  75.3W   30 KT  35 MPH
120H  13/0600Z 25.0N  76.2W   30 KT  35 MPH

$$
Forecaster Stewart

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