ATL: CRISTOBAL - Post-Tropical - Discussion

[summersquall]

000
WTNT44 KNHC 250233
TCDAT4

TROPICAL STORM CRISTOBAL DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042014
1100 PM EDT SUN AUG 24 2014

Cristobal is not a well-organized tropical cyclone at this time.
The deep convection has a ragged appearance, with little or no
banding features evident, and this convection is mainly
occurring well to the south of the estimated center location.
After adjusting for rain inflation, SFMR winds from aircraft
observations a few hours ago, indicated that the intensity is no
more than 40 kt. Also, the fixes from the Air Force and NOAA
planes, which were flying at altitudes of about 1000 and 8000 feet
respectively, indicated a southward tilt of the center with height.
This is consistent with some northerly shear over the storm as
suggested by water vapor imagery. Given the currently disorganized
state of Cristobal, not much intensification seems likely for the
next 12 hours or so. Afterwards, the global models are predicting a
little more favorable upper-tropospheric environment with
increasingly diffluent flow over the tropical cyclone. The official
intensity forecast is basically a blend of the SHIPS and LGEM
guidance, and only a little above the model consensus. By 120
hours, the global models depict the cyclone embedded within a
baroclinic zone, so extratropical transition should have occurred by
that time.

The motion has been rather erratic over the past several hours, but
my best estimate is about 350/4 kt. Cristobal is currently situated
near a col between 2 anticyclones in the mid-level flow, one over
the United States, and one over the central subtropical Atlantic.
The dynamical models indicate that, within a couple of days,
the steering of the tropical cyclone will become dominated by flow
on the northwest side of the Atlantic anticyclone and on the
southern side of a mid-latitude trough. Therefore, the motion is
expected to gradually bend to the right with some acceleration over
the next several days. The official track forecast is somewhat
faster than the previous one after 48 hours, but not as fast as the
latest dynamical model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT 25/0300Z 24.8N 73.1W 40 KT 45 MPH
12H 25/1200Z 25.4N 73.1W 40 KT 45 MPH
24H 26/0000Z 26.4N 72.8W 45 KT 50 MPH
36H 26/1200Z 27.8N 72.4W 50 KT 60 MPH
48H 27/0000Z 29.8N 71.8W 55 KT 65 MPH
72H 28/0000Z 33.5N 69.0W 65 KT 75 MPH
96H 29/0000Z 37.5N 62.0W 70 KT 80 MPH
120H 30/0000Z 44.0N 50.0W 60 KT 70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch

[AtlanticWind]

I wonder if the center could get pulled even further south under this burst on convection?

[Hammy]

NHC DISCUSSION

Interesting to read the first paragraph about the organization, then compare recon and satellite data just three hours later...

[bahamaswx]

Actual center is a good ways SSE of the 11pm position.

[blazess556]

2 a.m. NHC position was SSE of the 11 p.m. position.

11 p.m. 24.8 N 73.1 W

2 a.m. 24.5 N 72.9 W

[blazess556]

New center fix is 24.18 N 72.8W

[HurriGuy]

I dont understand why NHC puts 24.5N

[Riptide]

This ain't right, models will change if this keeps up. These mesoscale features cannot be properly modeled far out, like many have posted about already.

[bahamaswx]

Last VDM says 995mb, with 50kt winds.

[paintplaye]

This ain't right, models will change if this keeps up. These mesoscale features cannot be properly modeled far out, like many have posted about already.

The weakness by the east coast trough will remain open until late Tuesday evening. A mix of the trough moving northeast and another disturbance rotating around the sub tropical ridge will help send this to the north and east. This will accelerate once the sub tropical ridging starts pushing West

[JtSmarts]

I really don't think the southern relocation will affect Cristobal's course that much in the grand scheme of things. I think we would have to see something like a sustained southwesterly movement to see any change at all to the models. They have been in complete agreement for the last few runs except for the bams more recently.

[artist]

B. 24 deg 11 min N 072 deg 48 min W
last vdm

[Frank2]

Per the 5 am TCD shear and as seen here drier air, too:

http://www.ssd.noaa.gov/PS/TROP/floater ... imated.gif

[bahamaswx]

The southward drift seems to have stopped. Looks to me like it has headed slowly NNE in the past couple of hours.

[bahamaswx]

090800 2334N 07151W 8425 01511 //// +147 //// 195057 057 047 016 01
090830 2333N 07150W 8430 01508 //// +145 //// 195057 058 046 015 01
090900 2332N 07149W 8440 01497 //// +147 //// 194060 061 047 012 01
090930 2332N 07148W 8424 01514 //// +147 //// 193061 062 047 012 01
091000 2331N 07146W 8427 01511 0039 +151 //// 194060 062 051 016 01

Looks like the 5am advisory was too conservative.

[bahamaswx]

VDM from that pass supports 993mb

[Nimbus]

At 993 all Cristbal needs is a drop in shear and he could stack up and bomb.
Glad to hear the front is expected to linger, hopefully Cristobal will make it north of 25 today.

[bahamaswx]

Very badly sheared. LLC is completely exposed.

[NDG]

Exposed LLC started moving again slowly NE just like the global models have been persistent, not that the trough is pulling it, is more like getting caught in the southerly flow from the Atlantic subtropical ridge to the east of it before getting caught by another trough later tonight, like the NHC mentioned last night.

[hurrtracker79]

Exposed LLC started moving again slowly NE just like the global models have been persistent, not that the trough is pulling it, is more like getting caught in the southerly flow from the Atlantic subtropical ridge to the east of it before getting caught by another trough later tonight, like the NHC mentioned last night.

yes, the low level center is now moving north, but the convection appears to be not moving. looks like the low level center is completely exposed we could still see Reformation further south as long as we have wind shear.