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Tropical Depression NINE


Tropical Depression Nine Discussion Number   4
NWS National Hurricane Center Miami FL       AL092018
1100 AM AST Sat Sep 08 2018

The structure of Tropical Depression Nine is improving as the
ongoing shear diminishes, with the convection getting closer to the
low-level center.  However, recent scatterometer data indicates
that the system has not yet become a tropical storm, and the
initial intensity remains 30 kt.

The cyclone is still moving fairly slowly, with the initial motion
now 300/5.  The subtropical ridge to the north of the cyclone is
forecast to steer the system westward with an increasing forward
speed for at least the next 2-3 days.  After that time, there is
some uncertainty in the track forecast due to the formation of a
mid- to upper-level trough over the central Atlantic.  The Canadian
and UKMET models forecast the cyclone to slow down and turn
northwestward near the end of the forecast period due to the trough,
while the ECMWF and GFS show a continued westward motion.  The track
forecast follows the ECMWF/GFS scenario and shows a faster westward
motion than the previous forecast.  The new forecast also lies near
the various consensus models.

With the shear diminishing, conditions are becoming more favorable
for the cyclone to strengthen during the next 72 h.  However, there
are still concerns about dry air entraining into the system.  The
new intensity forecast is similar to the previous forecast with the
cyclone becoming a tropical storm in about 12 h and a hurricane in
about 72 h.  After 72 h, the system is expected to encounter
another round of shear, which is expected to cause some weakening.


INIT  08/1500Z 14.6N  36.0W   30 KT  35 MPH
 12H  09/0000Z 14.7N  36.9W   35 KT  40 MPH
 24H  09/1200Z 14.8N  38.5W   40 KT  45 MPH
 36H  10/0000Z 14.8N  40.8W   50 KT  60 MPH
 48H  10/1200Z 14.8N  43.5W   60 KT  70 MPH
 72H  11/1200Z 14.5N  49.0W   75 KT  85 MPH
 96H  12/1200Z 14.5N  55.0W   80 KT  90 MPH
120H  13/1200Z 14.5N  60.0W   75 KT  85 MPH

Forecaster Beven