[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 061456
TCDAT4

HURRICANE MATTHEW DISCUSSION NUMBER  34
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142016
1100 AM EDT THU OCT 06 2016

The satellite presentation of the hurricane has continued to
improve, with a distinct eye surrounded by very deep convection,
and T-numbers are oscillating around 6.0 on the Dvorak scale.  Data
from an Air Force reconnaissance plane traversing the eye of the
hurricane also indicate that Matthew has strengthened.  The initial
intensity is estimated at 120 kt, based mainly on SFMR data
and an eyewall dropsonde.

Environmental conditions appear favorable for additional
intensification today while Matthew approaches the east coast of
Florida.  After 24 hours, land interaction is likely to cause some
weakening, and later in the period increasing shear should cause a
more rapid decrease in winds. The NHC forecast is slightly above
most of the guidance during the first 24 hours due to the recent
intensification, and follows the weakening trend of the consensus
thereafter.

Aircraft fixes show that Matthew is moving toward the northwest or
325 degrees at 10 kt. The steering flow has not changed and Matthew
is expected to move around the western periphery of the subtropical
ridge located over the western Atlantic during the next 24 to 36
hours. After that time, the ridge will shift eastward allowing
the hurricane to move northward and then sharply turn eastward
while it becomes embedded within the mid-latitude westerlies. By
the end of the forecast period the steering pattern is forecast
to change again and a weakening cyclone is expected to turn
southward.

KEY MESSAGES:

1.  Matthew is likely to produce devastating impacts from storm
surge, extreme winds, and heavy rains in the northwestern Bahamas
today, and along extensive portions of the east coast of Florida
tonight.

2.  Evacuations are not just a coastal event.  Strong winds will
occur well inland from the coast, and residents of mobile
homes under evacuation orders are urged to heed those orders.

3.  Hurricane winds increase very rapidly with height, and residents
of high-rise buildings 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.

4.  When a hurricane is forecast to take a track roughly parallel
to a coastline, as Matthew is forecast to do from Florida through
South Carolina, it becomes very difficult to specify impacts at
any one location.  Only a small deviation of the track
to the left of the NHC forecast could bring the core of a major
hurricane onshore within the hurricane warning area in Florida and
Georgia.  Modest deviations to the right could keep much of the
hurricane-force winds offshore.  Similarly large variations in
impacts are possible in the hurricane watch and warning areas in
northeast Georgia and South Carolina.

5.  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.  In
addition, because the Flooding Map is based on inputs that extend
out only to about 72 hours, it best represents the flooding
potential in those locations within the watch and warning areas in
Florida and Georgia.

FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 25.1N  77.8W  120 KT 140 MPH
 12H  07/0000Z 26.4N  79.0W  125 KT 145 MPH
 24H  07/1200Z 28.3N  80.4W  125 KT 145 MPH
 36H  08/0000Z 30.2N  81.1W  115 KT 130 MPH
 48H  08/1200Z 31.7N  80.0W   95 KT 110 MPH
 72H  09/1200Z 32.5N  76.5W   75 KT  85 MPH
 96H  10/1200Z 30.5N  75.0W   50 KT  60 MPH
120H  11/1200Z 28.5N  76.0W   40 KT  45 MPH

$$
Forecaster Avila
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