ATL: KARL - Post-Tropical - Discussion

[GCANE]

Forecasted turn to the north starts later today - we'll see.

[wxman57]

Which looks stronger this morning, Karl or Invest 96L? 12Z ASCAT showed 96L has a well-defined circulation with at least 30kt winds (40kts flagged as rain-contaminated). Karl will definitely be recurving well east of the U.S.

[TheStormExpert]

Notice how the NHC keeps pushing back when Karl becomes a hurricane(always been 4-5 days out).

[tolakram]

live visible

http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=19&lon=-48&info=vis&zoom=1&width=1024&height=768&type=Animation&quality=92&palette=ir1.pal&numframes=8&mapcolor=gray&map=none

[cycloneye]

Gonzo will fly on Tuesday as well the P-3 Miss Piggy.

THE G-IV WILL FLY A RESEARCH MISSION AROUND TROPICAL STORM
KARL AT 20/1730Z.
THE P-3 WILL START RESEARCH MISSIONS EVERY 12 HOURS ON
KARL AT 20/1800Z

[cycloneye]

TROPICAL STORM KARL DISCUSSION NUMBER 21
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM AST MON SEP 19 2016

Visible satellite imagery shows Karl consists of a swirl of low
clouds with nearly all of the associated deep convection located to
the northeast of the exposed low-level center. The structure has
changed relatively little from six hours ago, and the initial wind
speed remains 35 kt based on the Dvorak Current Intensity estimate
from TAFB.

Karl is still being affected by 10-15 kt of southwesterly vertical
shear, and with the mid-level relative humidity in the surrounding
environment only 40-50 percent, the cyclone continues to struggle
to produce deep convection near its center and over the western
part of the circulation. However, the SHIPS guidance indicates
that the shear should continue to decrease during the next few
days, and mid-level moisture is likely to increase over 60 percent
by day 3. Therefore, only slight strengthening is anticipated
during the next 48 hours, but that should be followed by quicker
intensification on days 3-5, with Karl still expected to reach
hurricane intensity by the end of the forecast period. The updated
official intensity forecast is very close to the SHIPS guidance for
the entire forecast period, and it is just slightly below the
previous forecast after 24 hours.

The initial motion is just a little slower at 275/11 kt. Karl's
westward motion is the result of it being positioned south of the
Bermuda-Azores high. However, the cyclone is expected to reach a
break in the ridge located over the western Atlantic in a few days,
which will cause it to turn northwestward by day 3 and then
northward by day 5. The track models are tightly clustered through
day 3 before Karl makes its turn, but there is more spread on days
4 and 5 regarding where the turn will occur. The GFS and GFS
ensemble mean both take Karl farther west before it turns toward
the north, while the bulk of the other models make the turn east of
the previous forecast track. For the sake of continuity, the
updated official track forecast is very similar to the previous
forecast, and it lies relatively close to a consensus of the GFS
and ECMWF models.

FORECAST POSITIONS AND MAX WINDS

INIT 19/1500Z 18.6N 48.3W 35 KT 40 MPH
12H 20/0000Z 18.9N 50.3W 35 KT 40 MPH
24H 20/1200Z 19.5N 52.8W 40 KT 45 MPH
36H 21/0000Z 20.4N 55.2W 40 KT 45 MPH
48H 21/1200Z 21.6N 57.7W 45 KT 50 MPH
72H 22/1200Z 24.5N 62.3W 55 KT 65 MPH
96H 23/1200Z 27.5N 65.5W 70 KT 80 MPH
120H 24/1200Z 29.5N 65.0W 80 KT 90 MPH

$$
Forecaster Berg

[cycloneye]

 https://twitter.com/EricBlake12/status/777879631193976833

[wxman57]

NHC mentions keeping Karl a TS due to TAFB Dvorak estimates. I see the current Dvorak estimate is T1.5, which is about 25 kts - same as 96L, though 96L has convection over its center. Not sure where the NHC sees a Dvorak of 2.5 for Karl.

[cycloneye]

 https://twitter.com/BigJoeBastardi/status/777892430502821888




 https://twitter.com/EricBlake12/status/777893027138285569

[abajan]

Excerpt from the 11 AM Discussion:

Karl is still being affected by 10-15 kt of southwesterly vertical
shear, and with the mid-level relative humidity in the surrounding
environment only 40-50 percent, the cyclone continues to struggle
to produce deep convection near its center and over the western
part of the circulation. However, the SHIPS guidance indicates
that the shear should continue to decrease during the next few
days, and mid-level moisture is likely to increase over 60 percent
by day 3.

Question: Do they really mean that the SHIPS guidance indicates that the mid-level moisture is likely to increase [by] over 60 percent, or to over 60 percent? Because there's a significant difference between the two.

[Kazmit]

The latest cone doesn't take Karl very west, having the northward curve start while SSE of Bermuda. Most models take Karl farther west, and start the rather sharp recurve while SE of Bermuda.I wonder why?

[AutoPenalti]

Looks like Karl is moving to the WNW now, it hit north of the forecast point.

[cycloneye]

Another center relocation going on.Convection is now covering the LLC.

[SapphireSea]

The latest cone doesn't take Karl very west, having the northward curve start while SSE of Bermuda. Most models take Karl farther west, and start the rather sharp recurve while SE of Bermuda.I wonder why?

Deep layer westerlies occurring**** good bit south of Bermuda. Good to keep an eye on. The more intense Karl gets the better it will be for Bermuda. Tighter wind radii, sharper turn into the weakness. Once it feels the weakness and moves even slightly in tandem, with it; Karl will lift out in tandem with the trough. Think of a valley with a marvel (fluid and air particles). More often than not once it's influenced by the topographical change it does not matter where this valley moves. The marble will follow. In this case Karl.

Edit. Deep layer steering is S to N around Bermuda. Low level easterlies and mid to upper level SSW winds. The active trough coming off US east coast will change it a bit.

[Nimbus]

The TUTT on the west side of Karl is closing off which means it could roll W or even SW.
Karl is picking up convection possibly from the southerly shear, but also Karl is moving over warmer SST's into a moister environment.

[Kazmit]

Another center relocation going on.Convection is now covering the LLC.

Starting to look more like a TS now.

[Kazmit]

I see a very slight northward shift in the models following the recurve. Bermuda's hidden near that white track, at about 32N, 65W.

[cycloneye]

 https://twitter.com/NOAA_HurrHunter/status/777948089550249985

[JaxGator]

Convection is really blossoming. Big improvement since this morning (and the last few days but he's hanged on). Imo, it's strengthening.

[cycloneye]

TROPICAL STORM KARL DISCUSSION NUMBER 22
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016
ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
500 PM AST MON SEP 19 2016

Deep convection associated with Karl has increased during the day,
and the low-level center is now embedded beneath the convective
canopy. Dvorak intensity estimates from TAFB and SAB increased to
T2.5/35 kt and T2.0/30 kt, respectively, but these numbers do not
yet support an increase in the initial intensity of 35 kt that has
been carried in the previous few advisories. SHIPS and UW-CIMSS
shear analyses indicate that the southwesterly shear over Karl
remains 10-15 kt. However, the guidance shows the shear decreasing,
and the improving structure of Karl suggests that this may be
already occurring. In addition, moisture in the middle levels of
the atmosphere is expected to gradually increase, and SSTs will be
between 28-30C for the next five days. All these ingredients
suggest that strengthening is likely, and the official forecast
continues to show intensification starting slowly at first and then
becoming faster after 48 hours. This forecast is very close to a
consensus of the SHIPS and LGEM models, and the new official
forecast is essentially an update of the previous forecast.

The center of Karl jogged northwestward during the day, and the
long-term motion estimate is now west-northwestward, or 290/10 kt.
A west-northwestward motion is expected to continue for the next
couple of days while Karl moves along the southern edge of the
subtropical ridge. After that time, Karl is forecast to reach the
western edge of the ridge and should turn northward and then
northeastward on days 4 and 5. There is still some spread among
the track models when this turn is forecast to occur, and as a
result there is a lot of uncertainty on how much Karl will affect
Bermuda toward the end of the forecast period. Still, the overall
guidance envelope has not shifted much, and the updated official
forecast is very close to the previous one. This forecast is close
to the various consensus models, but it should be noted that the
GFS, GFS ensemble mean, and Florida Superensemble all show Karl
moving farther west before making the northward turn.

FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 19.3N 49.2W 35 KT 40 MPH
12H 20/0600Z 19.8N 51.1W 40 KT 45 MPH
24H 20/1800Z 20.6N 53.6W 40 KT 45 MPH
36H 21/0600Z 21.6N 56.0W 45 KT 50 MPH
48H 21/1800Z 22.9N 58.4W 50 KT 60 MPH
72H 22/1800Z 25.9N 62.6W 60 KT 70 MPH
96H 23/1800Z 29.0N 65.0W 75 KT 85 MPH
120H 24/1800Z 31.0N 63.0W 85 KT 100 MPH