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Tropical Depression FOUR


Tropical Depression Four Discussion Number   3
NWS National Hurricane Center Miami FL       AL042017
1100 AM AST Thu Jul 06 2017

A series of microwave images, an earlier NRL WindSAT scatterometer
overpass, and recent ASCAT-B surface wind retrievals indicate that
the surface circulation of the depression has become less organized.
The center remains near the eastern edge of an amorphous blob of
deep convection and is a bit farther south than previously thought.
Enhanced BD-curve infrared imagery also shows that the cloud tops
have warmed considerably during the past 6 hours. The initial
intensity is held at 25 kt for this advisory based on the
deteriorating cloud pattern and a blend of the TAFB and SAB
satellite intensity estimates.

Large-scale dry, sinking air associated with a previous Saharan Air
Layer outbreak continues to be the primary inhibiting factor
affecting the cyclone.  Global and ensemble guidance show the system
degenerating into a remnant low or trough in 3 days or less, due to
the aforementioned harsh thermodynamic environment and increasing
moderate westerly shear.  The official intensity forecast is
basically an update of the previous advisory and favors the
dynamical models.

The initial motion is estimated to be west-northwestward, or
285/18 kt.  The circulation center continues to be difficult to
locate, but the above-mentioned scatterometer pass was helpful in
obtaining the position estimate.  The depression is forecast to be
steered by the low- to mid-level flow associated with a building
subtropical ridge situated to its north over the next several days.
The new official forecast is about a half a degree south of the
previous one due to the initial position adjustment.  The NHC track
is close to the latest TVCN multi-model consensus.


INIT  06/1500Z 13.2N  42.6W   25 KT  30 MPH
 12H  07/0000Z 14.0N  45.3W   30 KT  35 MPH
 24H  07/1200Z 15.1N  49.3W   30 KT  35 MPH
 36H  08/0000Z 16.2N  52.9W   30 KT  35 MPH
 48H  08/1200Z 17.7N  56.6W   25 KT  30 MPH
 72H  09/1200Z 20.6N  62.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  10/1200Z 23.0N  67.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  11/1200Z...DISSIPATED

Forecaster Roberts