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.