Tropical Depression FOUR

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TROPICAL DEPRESSION FOUR DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042014
1100 PM AST SAT AUG 23 2014

Satellite imagery indicates that Tropical Depression Four has
changed little in organization during the past several hours.
While the convection remains somewhat ragged, a persistent area of
stronger convection has formed near the center.  Data from NOAA and
Air Force Reserve Hurricane Hunter aircraft indicate that maximum
sustained winds are near 30 kt, which is in agreement with the
satellite intensity estimate from TAFB.  The cirrus outflow is good
over the eastern semicircle and poor elsewhere.

The initial motion is a somewhat uncertain 320/8.  The cyclone
should continue moving northwestward and north-northwestward into a
developing break in the subtropical ridge cause by a mid- to upper-
level trough off of the U.S. east coast. As the trough begins to
lift out and steering currents weaken, a slow motion is expected in
36 to 48 hours.  The track guidance becomes very divergent at that
time. The UKMET and the NAVGEM models build enough ridging north of
the cyclone to steer it across Florida and into the Gulf of Mexico.
The Canadian model currently forecasts a quick right turn with the
cyclone moving well out to sea.  The ECMWF and the GFS keep a
stronger ridge east of the cyclone and thus forecast a more
northward motion east of the southeastern United States, followed by
a northeastward turn. However, the GFS does show a westward wobble
just north of the Bahamas before the turn.  The new forecast track
is nudged a little to the east of the previous track, and it lies a
little to the left of the TVCA consensus and the center of the
guidance envelope.  As mentioned in the previous discussion, the
confidence in the track forecast is lower than normal.

The large-scale models suggest that the cyclone should experience
light to moderate westerly or northwesterly vertical wind shear
throughout the forecast period.  The intensity guidance forecasts
less strengthening than earlier, which necessitates some downward
adjustment of the new intensity forecast.  Even with this change,
the new forecast is on the upper edge of the intensity guidance.
Overall, the forecast is close to the IVCN intensity consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 22.3N  72.6W   30 KT  35 MPH
 12H  24/1200Z 23.1N  73.4W   35 KT  40 MPH
 24H  25/0000Z 23.9N  74.0W   40 KT  45 MPH
 36H  25/1200Z 24.4N  74.3W   45 KT  50 MPH
 48H  26/0000Z 24.8N  74.6W   50 KT  60 MPH
 72H  27/0000Z 27.0N  76.0W   60 KT  70 MPH
 96H  28/0000Z 29.5N  77.0W   65 KT  75 MPH
120H  29/0000Z 32.5N  75.0W   70 KT  80 MPH

$$
Forecaster Beven

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