[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 300849
TCDAT4

HURRICANE MATTHEW DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142016
500 AM AST FRI SEP 30 2016

There are no data currently available from the inner core of
Matthew, so it is unclear whether the earlier rapid intensification
is continuing.  A well-defined elliptical eye is seen in data from
the Curacao radar.  However, the latest satellite imagery shows
that the central convection is somewhat asymmetric and that an eye
is yet to form.  Satellite intensity estimates are 90 kt from TAFB
and 77 kt from SAB.  Based on continuity from the previous advisory
and no improvement in the satellite signature, the initial intensity
is held at a possibly conservative 85 kt.  It is notable that the
rapid intensification has occurred despite an ongoing 20 kt of
southwesterly vertical wind shear.

The initial motion is 265/12.  There is little change to the track
forecast philosophy from the previous advisory.  A low- to
mid-level ridge to the north of Matthew should keep it moving
westward or south of westward for the next 36 hours with some
decrease in forward speed.  From 48-120 hours, the ridge is
forecast to weaken and shift eastward as a mid- to upper-level
trough moves into the central and eastern Gulf of Mexico.  This
evolution should cause Matthew to turn northwestward and then
northward.  There is a significant spread in where the turn will
occur and how fast Matthew will move afterwards.  The ECMWF and
UKMET are on the eastern side of the guidance envelope and slower
than the other models, while the GFS and Canadian models are to the
left of the center of the guidance envelope and much faster.  The
various consensus models split these differences in both track and
speed, and the new forecast track lies close to them.  Overall, the
new track is a little south of the previous track through 48 hours
and a little west of the previous track from 72-120 hours.

The intensity forecast is very problematic.  The ongoing shear has
so far done little to keep Matthew from intensifying.  Despite
this, the intensity guidance is in unanimous agreement that the
cyclone should weaken from 12-48 hours, most likely due to shear.
>From 48-96 hours, the shear is expected to diminish, and during that
time Matthew is expected to intensify until it interacts with land.
The intensity forecast will smooth through what could be some ups
and downs in intensity.  First, it assumes that the current
strengthening will continue for another 12-24 hours, with Matthew
reaching major hurricane strength.  Then, it keeps the intensity at
100 kt from 24-48 hours, followed by some intensification as the
shear lets up.  Weakening due to land interaction is forecast after
72 hours.  The intensity forecast lies near the upper edge of the
intensity guidance, but it is less intense than the HWRF model from
72-120 hours.


FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 14.0N  69.9W   85 KT 100 MPH
 12H  30/1800Z 13.8N  71.2W   95 KT 110 MPH
 24H  01/0600Z 13.7N  72.5W  100 KT 115 MPH
 36H  01/1800Z 13.9N  73.7W  100 KT 115 MPH
 48H  02/0600Z 14.5N  74.8W  100 KT 115 MPH
 72H  03/0600Z 17.0N  76.0W  105 KT 120 MPH
 96H  04/0600Z 20.5N  76.0W   90 KT 105 MPH...INLAND
120H  05/0600Z 24.5N  76.0W   85 KT 100 MPH...OVER WATER

$$
Forecaster Beven
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