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Tropical Storm MATTHEW Forecast Discussion


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000
WTNT44 KNHC 290905
TCDAT4

TROPICAL STORM MATTHEW DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142016
500 AM AST THU SEP 29 2016

Matthew is currently experiencing 15-20 kt of southwesterly
vertical wind shear, with the low-level center located near the
western edge of the main convective mass.  An earlier Air Force
Reserve Hurricane Hunter mission reported 850 mb flight-level winds
of 65-70 kt and estimated surface winds of 50-55 kt from the SFMR
instrument.  Based on these data, the initial intensity remains 55
kt.  The aircraft reported a central pressure of 1002 mb on its
last pass through the center.

The initial motion is 275/14.  Matthew is currently on the south
side of a low- to mid-level subtropical ridge.  This feature should
steer the storm westward or even south of west during the next 48
hours.  After that time, Matthew is expected to approach the
western end of the ridge as a mid- to upper-level trough develops
over the Gulf of Mexico.  While this combination is expected to
cause the cyclone to turn generally northward, there is significant
disagreement between the dynamical models on where the turn will
occur and how fast Matthew will move northward.  The forecast track
is in best agreement with the GFS and GFS ensemble mean in bringing
the center to eastern Cuba by 120 hours, although it is slower than
those models. The Canadian model is a little west of the forecast
track. The ECMWF and UKMET are to the east of the forecast track and
much slower, bringing the center to the island of Hispaniola.
Overall, the new forecast track is nudged a little south of the
previous track for the first 72 hours, then is similar to the
previous track.  Users are reminded that the average NHC track
errors at days 4 and 5 are on the order of 180 and 240 miles,
respectively.

The current shear is likely to gradually diminish during the next
72 hours, and this should allow continued gradual development.
After that time, there is also disagreement in the models regarding
the forecast shear, with the GFS showing a more favorable pattern
than the ECMWF.  If the GFS upper-level winds are correct, Matthew
could strengthen more than currently forecast as show by the HWRF.
However, given the uncertainty, the new intensity forecast is the
same as the previous forecast and is in best agreement with the
intensity consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0900Z 14.0N  64.7W   55 KT  65 MPH
 12H  29/1800Z 14.1N  66.7W   60 KT  70 MPH
 24H  30/0600Z 14.1N  69.2W   65 KT  75 MPH
 36H  30/1800Z 13.9N  70.8W   70 KT  80 MPH
 48H  01/0600Z 13.8N  72.2W   75 KT  85 MPH
 72H  02/0600Z 14.5N  74.0W   75 KT  85 MPH
 96H  03/0600Z 17.5N  75.0W   85 KT 100 MPH
120H  04/0600Z 20.5N  75.5W   80 KT  90 MPH...INLAND

$$
Forecaster Beven