ATL: FIONA - Post-Tropical - Discussion

[LemieT]

Fiona is reminding me of Kirk in 2018 as it approached the Caribbean. Very touch and go whether it survives past tomorrow.

[jlauderdal]

I notice 12Z EC ensembles do not agree with the operational run. They turn it north and keep it east of the U.S., mostly.

https://www.weathernerds.org/tc_guidance/images/AL07_2022091512_ECENS_large.png?1663270910

Toss the operational, lets see what gfs happy hour says.

[KWT]

I'm not sure if anyone else is clocking this but on the last hour or two of that satellite loop I'm noticing as the current /LLC is elongating there appears to be quite a strong inflow of low level clouds into the convection (SE of the LLC).

I'm wondering whether we are about to see a shift and a new LLC form further east near the convection, or at least a competing center try to spin up. Some of the higher resolution models were suggesting that might happen.

[CrazyC83]

50 kt might be the best estimate with 46 SFMR and 67 FL (reduces to 49).

[Sciencerocks]

[PTrackerLA]

5pm NHC Discussion:


Tropical Storm Fiona Discussion Number 6
NWS National Hurricane Center Miami FL AL072022
500 PM AST Thu Sep 15 2022

Deep convection has been sheared more than a degree to the east of
the center for much of the day, and as a result, the low-level
center and circulation have become slightly less defined and
elongated, respectively. That said, an Air Force Reserve Hurricane
Hunter aircraft measured a peak 925-mb flight-level wind of 65 kt
and SFMR winds as high as 46 kt. Assuming some undersampling of
the surface winds, the initial intensity is set at 50 kt. This is
in agreement with ASCAT-C data from earlier today, which showed an
area of 45-50 kt winds to the northeast of the center.

Fiona appears to have lost a little bit of latitude since earlier
this morning, but the motion remains westward, or 270 degrees at 12
kt. Track models are in good agreement during the next 2 to 3
days, showing a low- to mid-level ridge steering Fiona westward
across the Leeward Islands and over the far northeastern Caribbean
Sea through Sunday. The HWRF is the only outlier during this
period and appears to have a track too far to the north due to an
unrealistically high intensity. After day 3, there is more
divergence among the track models, with the stronger solutions
(i.e., the GFS) indicating a sharper northwestward turn toward a
weakness in the subtropical ridge. The weaker solutions (i.e., the
ECMWF and HMON) keep Fiona on a westward or west-northwestward
track, moving near or over Hispaniola. As a result, the 4- and
5-day forecasts are of lower-than-normal confidence, and ensembles
from the main global models suggest that the cyclone could end up
anywhere from eastern Cuba to well to the northeast of the
Bahamas by the end of the forecast period. For now, the official
track forecast is nudged southward and westward from the previous
forecast, accounting for the adjusted initial position and the
overall trend in the track guidance.

Moderate, and even possibly strong, westerly shear is likely to
continue for much of the 5-day forecast period. Given these
conditions, the NHC intensity forecast flatlines Fiona's intensity
at 50 kt for the next 60 hours, with the caveat that fluctuations
are possible related to the convective structure of the cyclone at
any time. Fiona is forecast to slow down by the 3-5 day time
frame, and the slower motion could allow for the circulation to
become more vertically stacked, even in the face of continued
shear. As a result, some gradual strengthening is indicated at the
latter part of the forecast period. Given uncertainties in how
much Fiona might interact with the islands of the Greater Antilles,
the NHC intensity forecast lies about 5-10 kt below the IVCN and
HCCA consensus aids.


Key Messages:

1. Tropical storm conditions are expected in the Leeward Islands
within the warning area by Friday evening. Tropical storm
conditions are possible within the watch area across the Virgin
Islands beginning on Saturday, and then reaching Puerto Rico late
Saturday and Saturday night.

2. Heavy rains from Fiona will reach the northern Leeward Islands
Friday afternoon, spreading to the British and U.S. Virgin Islands
and Puerto Rico Saturday into Sunday morning, and reaching eastern
Hispaniola Sunday. This rainfall may produce flash and urban
flooding, along with isolated mudslides in areas of higher terrain.
Considerable flood impacts are possible across eastern portions of
Puerto Rico.

3. Fiona is expected to move near Hispaniola early next week, and
watches could be required for parts of the island on Friday.


FORECAST POSITIONS AND MAX WINDS

INIT 15/2100Z 16.3N 55.4W 50 KT 60 MPH
12H 16/0600Z 16.3N 57.3W 50 KT 60 MPH
24H 16/1800Z 16.5N 59.8W 50 KT 60 MPH
36H 17/0600Z 16.8N 62.1W 50 KT 60 MPH
48H 17/1800Z 17.1N 64.1W 50 KT 60 MPH
60H 18/0600Z 17.3N 65.8W 50 KT 60 MPH
72H 18/1800Z 17.7N 67.1W 55 KT 65 MPH
96H 19/1800Z 19.3N 69.2W 60 KT 70 MPH
120H 20/1800Z 21.4N 71.1W 60 KT 70 MPH

[Nimbus]

Fiona appears to have lost a little bit of latitude since earlier
this morning, but the motion remains westward, or 270 degrees at 12
kt.

Recon found no flat bottom in the pressure gradient yet so this could spin up if the shear lets up later in the forecast. Next 60 hours there is model agreement on a threat to the Leeward Islands and there are some pretty stiff tropical storm force winds in the northeast quadrant. Looks like it is maintaining its strength for now and there will be several recon passes to verify whether we are getting a rise from the initial 1006 mb.

[chaser1]

I'm not sure if anyone else is clocking this but on the last hour or two of that satellite loop I'm noticing as the current /LLC is elongating there appears to be quite a strong inflow of low level clouds into the convection (SE of the LLC).

I'm wondering whether we are about to see a shift and a new LLC form further east near the convection, or at least a competing center try to spin up. Some of the higher resolution models were suggesting that might happen.

I see what you are seeing but then you'd have to make the case that either point of surface convergence is thwarting the other from better developing vertical structure. If we were to see the LLC continue to distance itself from the MLC, then it would unwind over a couple days' time. Until then though, I don't think it would be reasonable for a second center to organize further east sufficiently to better allow a new LLC to quickly align and improve it's vertical structure. If/when the present LLC ceases to disrupt inflow then I could see an eastward reformation. That would change everything too because suddenly we would no longer be looking at shallow fast westward moving disturbance, but perhaps a newly deepening disturbance moving slow enough to better develop and possibly begin to stair-step WNW to NW off the bat. That would change timing, land interaction, and a far more likelihood of an OTS track. I would think we'd need to see at least a bit more separation between the LLC and MLC first; That or perhaps the seeing the present LLC taking a southwest motion suggesting it having become so shallow that it's motion was now becoming enveloped (or influenced) by the increasingly stacked low developing immediately to it's east. For the immediate though, NHC will continue to track Tropical Swirl Fiona westward. Given the recon's sampled winds I think we'll have to see the LLC become a bit more elongated before any downgrade to TD (or straight to wave) occurs. I'd guess after first daylight around 12Z tomorrow?

[Hammy]

Another example of how robust the circulation can become even in the face of shear with systems that form from monsoonal waves vs the usual compact ones.

[chaser1]

I'm actually fascinated by NHC confidence of Fiona at least maintaining organization and intensity over the next few days?!

[aspen]

Another example of how robust the circulation can become even in the face of shear with systems that form from monsoonal waves vs the usual compact ones.

That could end up as its biggest limiting factor once it gets into favorable conditions, just like Earl. We’ll have to wait and see if Fiona becomes another system with a way too broad wind field, or if interactions with the islands tighten it up.

[LarryWx]

Fiona lost 0.3 degrees of latitude the last 6 hours.

[Hurricane Mike]

I'm skeptical this moves north anytime soon.

Here's today's video update:
https://www.youtube.com/watch?v=0jEFvDJXfSs

[jlauderdal]

Fiona lost 0.3 degrees of latitude the last 6 hours.

Every mile matters now and in the future

[Hammy]

Another example of how robust the circulation can become even in the face of shear with systems that form from monsoonal waves vs the usual compact ones.

That could end up as its biggest limiting factor once it gets into favorable conditions, just like Earl. We’ll have to wait and see if Fiona becomes another system with a way too broad wind field, or if interactions with the islands tighten it up.

Earl's winds were running behind the pressure flight winds the entire time and was in a generally lower background pressure environment, which isn't the case here. The biggest question mark at this point is land, as a few degrees could mean the difference between a Caribbean cruiser, recurve, or plowing into Hispaniola.

[Sciencerocks]

Fiona lost 0.3 degrees of latitude the last 6 hours.

Every mile matters now and in the future

Exactly, if it goes directly over the DR/Haiti it will be far shallower and that will mean a more westerly track. Maybe even running straight down cuba. I wouldn't be shocked.

[jlauderdal]

Fiona lost 0.3 degrees of latitude the last 6 hours.

Every mile matters now and in the future

Exactly, if it goes directly over the DR/Haiti it will be far shallower and that will mean a more westerly track. Maybe even running straight down cuba. I wouldn't be shocked.

Euro gets support from the happy hour gfs, strange season for sure.

[tolakram]

IR floater. The entire blob is moving south now. Change in shear direction?

https://weather.cod.edu/satrad/?parms=meso-meso1-13-96-1-100-1&checked=map&colorbar=undefined

[jlauderdal]

IR floater. The entire blob is moving south now. Change in shear direction?

https://weather.cod.edu/satrad/?parms=meso-meso1-13-96-1-100-1&checked=map&colorbar=undefined

Blob tracking 2022, IR is good for blob tracking

[Wampadawg]

She is a rollercoaster with more ups and downs ( turns?) model battles, what else will she bring?