ATL: FRED - Post-Tropical - Discussion

[AtlanticWind]

https://www.star.nesdis.noaa.gov/GOES/s ... &length=24

Nice Outflow established

[Shell Mound]

Personally, I think the faster-than-expected forward speed in the short term will likely cap any further organisation until PTC Six nears the eastern Gulf.

Its speed of about 16mph should be no hindrance

I respectfully disagree. A forward speed of 14 kt contributes to net shear that prevents a centre from becoming vertically stacked. Most EPS members no longer show significant intensification until PTC Six reaches the eastern Gulf of Mexico. A faster speed in the short term means a reduced risk of heavy rainfall and strong winds from Puerto Rico to the Bahamas and South Florida. At this point I don’t think this will be much more than a depression or weak storm near the Florida Keys. Any further development would likely occur over the eastern Gulf of Mexico and threaten portions of the Big Bend and/or Florida Panhandle.

[AtlanticWind]

Personally, I think the faster-than-expected forward speed in the short term will likely cap any further organisation until PTC Six nears the eastern Gulf.

Its speed of about 16mph should be no hindrance

I respectfully disagree. A forward speed of 14 kt contributes to net shear that prevents a centre from becoming vertically stacked. Most EPS members no longer show significant intensification until PTC Six reaches the eastern Gulf of Mexico. A faster speed in the short term means a reduced risk of heavy rainfall and strong winds from Puerto Rico to the Bahamas and South Florida. At this point I don’t think this will be much more than a depression or weak storm near the Florida Keys. Any further development would likely occur over the eastern Gulf of Mexico and threaten portions of the Big Bend and/or Florida Panhandle.

Irma , Andrew, Ivan. I could name storms all day that had no problem at that speed
This systems problems it has to overcome is dry air and land interaction

[Shell Mound]

Its speed of about 16mph should be no hindrance

I respectfully disagree. A forward speed of 14 kt contributes to net shear that prevents a centre from becoming vertically stacked. Most EPS members no longer show significant intensification until PTC Six reaches the eastern Gulf of Mexico. A faster speed in the short term means a reduced risk of heavy rainfall and strong winds from Puerto Rico to the Bahamas and South Florida. At this point I don’t think this will be much more than a depression or weak storm near the Florida Keys. Any further development would likely occur over the eastern Gulf of Mexico and threaten portions of the Big Bend and/or Florida Panhandle.

Irma , Andrew, Ivan. I could name storms all day that had no problem at that speed

...HURRICANE IRMA RAPIDLY INTENSIFYING OVER THE EASTERN ATLANTIC...
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 10 MPH...17 KM/H

....ANDREW BECOMES THE FIRST HURRICANE OF THE 1992 SEASON...
ANDREW IS MOVING TOWARD THE WEST NORTHWEST NEAR 10 MPH...17 KM/HR
...AND THIS GENERAL MOTION IS EXPECTED TO TODAY.

Source

Those storms were already mature while moving fairly rapidly. However, nascent systems such as this need to slow down in order to consolidate.

[AtlanticWind]

Iva was moving 16 knots when it formed , when the speeds are in excess of 20 knots
It becomes more difficult .


Looked it up Ivan was moving 15 to 16 knots from depression to hurricane

[AtlanticWind]

Potential Tropical Cyclone Six Discussion Number 3 NWS National Hurricane Center Miami FL AL062021 500 AM AST Tue Aug 10 2021 The disturbance moved through the southern Leeward Islands a few hours ago. Based on surface observations from the islands, the system still does not have a well-defined circulation. Although the satellite appearance shows some increase in organization, the surface data suggest no significant strengthening has occurred thus far. The current intensity estimate is held at 30 kt in agreement with a Dvorak estimate from SAB. A NOAA Hurricane Hunter aircraft is scheduled to investigate the disturbance later this morning and should provide an updated intensity estimate, and also determine whether the system has become a tropical cyclone. The disturbance continues moving west-northwestward, or about 295/15 kt. The flow on the south side of a strong subtropical ridge should maintain the west-northwestward track for the next 72 hours or so, with some slowing of forward speed by midweek. Beyond that time, a turn toward the northwest with further deceleration is likely while the system moves near the western periphery of the ridge. The official track forecast is very similar to the previous one and in good agreement with the latest simple and corrected multi-model consensus tracks. Users are reminded that the average track errors at days 4 and 5 are 175 miles and 200 miles, respectively. Dynamical conditions appear to be conducive for intensification during the next 24 hours or so, with low vertical shear and pronounced upper-level outflow over the system. The main hindrance for strengthening today and tonight appears to be some dry mid-tropospheric air in the environment, as shown by the global models. Since the projected track takes the disturbance or cyclone over the mountainous land mass of Hispaniola, some weakening and disruption of the circulation is likely in 36 hours or so. Later in the forecast period, the dynamical guidance shows some increase in westerly shear which could also inhibit strengthening. The official intensity forecast closely follows the NOAA corrected consensus forecast technique, HCCA. There is significant uncertainty in 4-5 day intensity forecasts, however. KEY MESSAGES: 1. The system is forecast to become a tropical storm as it moves over the northeastern Caribbean Sea today. Tropical storm conditions are expected in portions of the U.S. Virgin Islands and Puerto Rico beginning this afternoon, and in the Dominican Republic by Wednesday. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas by late Wednesday. 2. Heavy rainfall could lead to flash, urban, and small stream flooding and potential mudslides across the U.S. Virgin Islands and Puerto Rico. The greatest threat for flooding impacts will be across the eastern and southeastern portions of Puerto Rico. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the Bahamas, and Cuba later this week, although the forecast is more uncertain than usual since the system is still in its formative stage. Interests in these areas should monitor the system's progress and updates to the forecast. 4. Interests in the remainder of the Bahamas and Florida should monitor updates to the forecast for this system, but it is too soon to determine what if any impacts could occur there by late this week or this weekend given the uncertainty in the long-range forecast. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 15.7N 62.2W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 10/1800Z 16.7N 64.6W 40 KT 45 MPH...TROPICAL CYCLONE 24H 11/0600Z 17.9N 67.4W 45 KT 50 MPH 36H 11/1800Z 19.0N 70.1W 30 KT 35 MPH...INLAND 48H 12/0600Z 20.1N 72.6W 30 KT 35 MPH 60H 12/1800Z 21.1N 74.9W 30 KT 35 MPH 72H 13/0600Z 22.0N 77.0W 35 KT 40 MPH 96H 14/0600Z 24.4N 80.8W 40 KT 45 MPH 120H 15/0600Z 26.8N 83.1W 50 KT 60 MPH $$ Forecaster Pasch

[USTropics]

A forward speed of 15 kts is not enough to create westerly shear to inhibit development. PTC 6 is currently in a low shear environment, we can see this in the GFS sounding:



If there was significant westerly shear, we would be seeing dry air entrainment directly from the west, and a displacement of the mid-level vorticity to the east. Instead, dry air is being rotated in from the SW, and any displacement of a MLC is to the SW (likely due to the convection building to the north due to the dry-air entrainment wrapping around from the SW).



There is no evidence of westerly shear in water vapor imagery either (this would be evident in the outflow pattern):


From the 5AM discussion:

Dynamical conditions appear to be conducive for intensification
during the next 24 hours or so, with low vertical shear and
pronounced upper-level outflow over the system. The main
hindrance for strengthening today and tonight appears to be some
dry mid-tropospheric air in the environment, as shown by the global
models.

[xironman]

Didn't we just deal with Elsa strengthening at a high speed?

[SFLcane]

Didn't we just deal with Elsa strengthening at a high speed?

Yep, no speed problems here whatsoever.

[Dean4Storms]

There isn’t a forward speed or shear problem currently or going forward the next couple days, it’s dry air at mid levels and large islands in its path.

[SFLcane]

Have a feeling it’s going to relocate north but we will see what recon finds. It could be closed now

[USTropics]

The main hinderance for PTC 6, as has been mentioned for the past few days, is dry mid-level air. As PTC 6 attempts to deepen, and the air mass begins to expand in response, it inevitably leads to dry air being pulled in from the SW, and this needs to be mixed out through the air columns. PTC 6 is nearly devoid of convection in the southern inflow channel, and convection in the SW quadrant is unable to build with heights due to the stability in the air column (see shortwave IR imagery below). This is why we continue to see PTC 6 be a northern weighted system—convection is able to build with height in this region (air density and weight is less in the air column) and this creates lower pressure at the surface to the north. It would not shock me, given the disorganized LLC, if we see slight northern adjustments as the LLC propagates more towards the lower pressure and deeper convection. This process will continue until PTC 6 is able to properly push enough sustainable convection to the west to raise RH values in front of the circulation.

[SFLcane]

The main hinderance for PTC 6, as has been mentioned for the past few days, is dry mid-level air. As PTC 6 attempts to deepen, and the air mass begins to expand in response, it inevitably leads to dry air being pulled in from the SW, and this needs to be mixed out through the air columns. PTC 6 is nearly devoid of convection in the southern outflow channel, and convection in the SW quadrant is unable to build with heights due to the stability in the air column (see shortwave IR imagery below). This is why we continue to see PTC 6 be a northern weighted system—convection is able to build with height in this region (air density and weight is less in the air column) and this creates lower pressure at the surface to the north. It would not shock me, given the disorganized LLC, if we see slight northern adjustments as the LLC propagates more towards the lower pressure and deeper convection. This process will continue until PTC 6 is able to properly push enough sustainable convection to the west to raise RH values in front of the circulation.

https://s6.gifyu.com/images/goes16_vis-swir_06L_202108100705.gif

Yes

[jlauderdal]

There isn’t a forward speed or shear problem currently or going forward the next couple days, it’s dry air at mid levels and large islands in its path.

Elsa did ok at 25+, 25 would actually help this one get past the shredder quicker and into a more favorable setup although there does appear to be a shear issue after the shredder

[SFLcane]

The main hinderance for PTC 6, as has been mentioned for the past few days, is dry mid-level air. As PTC 6 attempts to deepen, and the air mass begins to expand in response, it inevitably leads to dry air being pulled in from the SW, and this needs to be mixed out through the air columns. PTC 6 is nearly devoid of convection in the southern outflow channel, and convection in the SW quadrant is unable to build with heights due to the stability in the air column (see shortwave IR imagery below). This is why we continue to see PTC 6 be a northern weighted system—convection is able to build with height in this region (air density and weight is less in the air column) and this creates lower pressure at the surface to the north. It would not shock me, given the disorganized LLC, if we see slight northern adjustments as the LLC propagates more towards the lower pressure and deeper convection. This process will continue until PTC 6 is able to properly push enough sustainable convection to the west to raise RH values in front of the circulation.

https://s6.gifyu.com/images/goes16_vis-swir_06L_202108100705.gif

Yes

 https://twitter.com/andyhazelton/status/1425036526937952279

[Blown Away]

Lots of bubbling convection, it's maintained the look of "Potential" for 24 hours...

[Blown Away]

The main hinderance for PTC 6, as has been mentioned for the past few days, is dry mid-level air. As PTC 6 attempts to deepen, and the air mass begins to expand in response, it inevitably leads to dry air being pulled in from the SW, and this needs to be mixed out through the air columns. PTC 6 is nearly devoid of convection in the southern outflow channel, and convection in the SW quadrant is unable to build with heights due to the stability in the air column (see shortwave IR imagery below). This is why we continue to see PTC 6 be a northern weighted system—convection is able to build with height in this region (air density and weight is less in the air column) and this creates lower pressure at the surface to the north. It would not shock me, given the disorganized LLC, if we see slight northern adjustments as the LLC propagates more towards the lower pressure and deeper convection. This process will continue until PTC 6 is able to properly push enough sustainable convection to the west to raise RH values in front of the circulation.

https://s6.gifyu.com/images/goes16_vis-swir_06L_202108100705.gif

Yes

https://twitter.com/andyhazelton/status/1425036526937952279

Nice summary! I think PTC6 is going to look like this for a few days and maybe starts to pull together @75W...

Interested to see 12z plot, NHC has PTC6 at 16.7N @2pm EST today. The bubbling convection is already near that latitude and the visible may reveal an exposed circulation to the S if there hasn't been slight relocation to the NE. JMHO

[NDG]

Much better defined circulation this morning compared to when to bed early last night.
I think is centered to the west of Guadeloupe/Dominica.

[eastcoastFL]

Held its own overnight and looks to be on its way to becoming Fred sometime today

[eastcoastFL]

Anticyclone parked right over PTC6 for now