[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 070857
TCDAT4

HURRICANE MATTHEW DISCUSSION NUMBER  37
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142016
500 AM EDT FRI OCT 07 2016

The satellite appearance of Matthew has become rather disheveled
looking in infrared satellite imagery since the previous advisory.
Land-based Doppler radar data indicate that Matthew has been going
through an eyewall replacement cycle for the past 12 hours or so,
but the inner eyewall has yet to dissipate within the 35-40 nmi wide
outer eyewall. Both Doppler velocity data and recon SFMR surface
winds and flight-level winds indicate that hurricane-force winds are
and have been occuring within the outer eyewall just 5-10 nmi east
of the Florida coastline. Although the central pressure has
remained steady between 938-940 mb, the intensity has been lowered
to 105 kt based on 700-mb flight-level winds of 118 kt and several
patches of Doppler velocities of 120-122 kt between 5000-7500 feet.

The initial motion estimate is 330/12 kt. For the next 48 hours,
Matthew is expected to move northward and then northeastward around
the western periphery of a deep-layer subtropical ridge. After that
time, a weakening Matthew is expected to turn slowly southeastward
and then southward as the cyclone gets cut off from the influence of
the mid-latitude westerlies and becomes embedded within the
aforementioned large-scale high pressure ridge. The latest model
guidance has shifted to the left of the previous forecast track
after 36 hours, and the official forecast has been nudged in that
direction, but remains well to the right of the model consensus and
close to the GFS-ECMWF consensus.

Matthew is expected to slowly weaken some more during the next 12
hours or so while the cyclone completes the eyewall replacement
cycle. By 24 hours and beyond, more significant weakening is
expected due to the combination of strong southwesterly vertical
shear increasing to more than 30 kt and entrainment of very dry
mid-level air with humidity values less than 20 percent. The new
intensity forecast closely follows the consensus model IVCN.

Special thanks to the Air Force Reserve and NOAA Hurricane Hunters
for their tireless efforts in having already completed more than 90
center or eye fixes.

KEY MESSAGES:

1.  Matthew is likely to produce devastating impacts from storm
surge, extreme winds, and heavy rains along extensive portions of
the east-central and northeast coast of Florida today.

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.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 28.2N  80.0W  105 KT 120 MPH
 12H  07/1800Z 29.6N  80.6W  100 KT 115 MPH
 24H  08/0600Z 31.5N  80.5W   90 KT 105 MPH
 36H  08/1800Z 32.6N  79.2W   80 KT  90 MPH
 48H  09/0600Z 33.1N  77.7W   65 KT  75 MPH
 72H  10/0600Z 31.5N  74.5W   50 KT  60 MPH
 96H  11/0600Z 29.0N  75.0W   40 KT  45 MPH
120H  12/0600Z 27.0N  76.5W   35 KT  40 MPH

$$
Forecaster Stewart
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