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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
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.
FORECAST POSITIONS AND MAX WINDS
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