ATL: FIONA - Post-Tropical - Discussion

[Nimbus]

12Z ECMWF may have updated upper air data.

The TUTT that was being pinched is closing off and the new weakness to its west is not digging quite as aggressively.



http://weather.msfc.nasa.gov/GOES/goeseasthurrwv.html

[cycloneye]

BULLETIN
TROPICAL STORM FIONA ADVISORY NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 PM AST FRI AUG 19 2016

...FIONA WEAKENS SLIGHTLY...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...18.1N 44.4W
ABOUT 1130 MI...1820 KM ENE OF THE LESSER ANTILLES
ABOUT 1355 MI...2180 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES



TROPICAL STORM FIONA DISCUSSION NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 PM AST FRI AUG 19 2016

Fiona continues to produce bursts of convection north of the
center, although the center is now mostly exposed to the south of
the latest burst. An earlier RapidScat overpass suggested that
tropical-storm-force winds were at best only occurring in the
northwest quadrant, and based on these data and the loss of
organization since this morning the initial intensity is decreased
to 35 kt.

The initial motion is 295/9. A low- to mid-level ridge north of the
cyclone is steering Fiona west-northwestward, and this motion
should continue with some increase in forward speed during the next
48-72 hours. After that time, a developing weakness in the ridge
caused by a frontal system moving eastward from the United States
should cause Fiona to turn northwestward and north-northwestward.
The guidance has again shifted westward between 72-120 hours. Thus,
as in the previous advisory that portion of the track is also nudged
westward, but it remains to the east of the various consensus
models.

A combination of a dry air mass, increasing vertical wind shear, and
convergent upper-level flow should cause Fiona to continue to
weaken. The intensity guidance has mostly trended toward lower
intensities since the last advisory, with the ECMWF model now
forecasting Fiona to weaken to a trough before 120 hours. Based on
this, the intensity forecast now calls for Fiona to become a
remnant low after 72 hours. That being said, the environmental
conditions might get less hostile by 120 hours, and the UKMET/
Canadian models suggest the possibility of re-intensification at
that time. In deference to those models, the official forecast does
not call for dissipation during this forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 18.1N 44.4W 35 KT 40 MPH
12H 20/0600Z 18.9N 46.0W 35 KT 40 MPH
24H 20/1800Z 19.9N 48.2W 35 KT 40 MPH
36H 21/0600Z 21.1N 50.7W 30 KT 35 MPH
48H 21/1800Z 22.1N 53.1W 30 KT 35 MPH
72H 22/1800Z 24.5N 57.5W 25 KT 30 MPH
96H 23/1800Z 26.5N 60.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 24/1800Z 28.5N 61.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Beven

[gatorcane]

Let's not forget Fiona folks as there is still good convection firing and it appears it is turning more WNW with time. Euro sends this quite a bit more west though degenerates her.

Wide-view loop below:

[Caneman12]

Fiona will degenerate soon the firing of convection is not even over the center just north of the circulation expect this to be gone really soon

[NDG]

Yeap, Fiona could still be a player down the road, but if first needs to survive the next 3-4 days.

[Kazmit]

Fiona weakening now due to dry air and shear, but could restrengthen later. From latest discussion from the NHC:

A combination of a dry air mass, increasing vertical wind shear, and
convergent upper-level flow should cause Fiona to continue to
weaken. The intensity guidance has mostly trended toward lower
intensities since the last advisory, with the ECMWF model now
forecasting Fiona to weaken to a trough before 120 hours. Based on
this, the intensity forecast now calls for Fiona to become a
remnant low after 72 hours. That being said, the environmental
conditions might get less hostile by 120 hours, and the UKMET/
Canadian models suggest the possibility of re-intensification at
that time. In deference to those models, the official forecast does
not call for dissipation during this forecast period.

[tolakram]

Blowing up, and interestingly the GFS shows a strengthening system for 36 hours.

live ir
http://weather.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-E%20HURRICANE&lat=19&lon=-40&info=ir&zoom=1&width=1024&height=725&type=Animation&quality=90&palette=ir3.pal&numframes=10&map=county&mapcolor=gray&map=none

[Hammy]

NHC may have been a bit premature in lowering the winds. Hopefully the next ASCAT pass will go right over it because I have a hard time believing it's only 35kt.

[NDG]

Fiona still holding its own.

[cycloneye]

TROPICAL STORM FIONA DISCUSSION NUMBER 13
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
1100 PM AST FRI AUG 19 2016

A 2346 UTC ASCAT-B overpass helped to locate the center, which is
beneath the cirrus canopy but along the southern edge of the deep
convection. The scatterometer pass suggested that the maximum
winds could be as high as 40 kt, but the highest vectors had
questionable directions and were on the edge of the pass.
Therefore, the intensity remains 35 kt, which is supported by
subjective and objective satellite intensity estimates.

Southwesterly vertical shear has increased to about 20 kt and is
forecast to go up further during the next 48 hours or so. Given the
increasing shear, a relatively dry middle troposphere, and Fiona's
small size, the cyclone is expected to gradually degrade during the
next few days. The intensity and global models either maintain
Fiona's intensity or show weakening through the forecast period, and
the ECMWF even opens the system up into a trough by day 3 or 4.
Given that Fiona will likely struggle to maintain deep convection
as environmental conditions worsen, the NHC forecast now shows the
cyclone degenerating into a remnant low by day 3. Although a
remnant low is carried through day 5, dissipation is possible before
the end of the forecast period.

The initial motion remains west-northwestward but a little faster
at 295/10 kt. The track models are in good agreement on Fiona
accelerating a bit along this heading during the next 48 hours, and
no significant changes to the NHC forecast was required during that
time. After 48 hours, however, the track forecast is highly
contingent on Fiona's status as a tropical cyclone, a remnant low,
or a trough. The ECMWF, which dissipates the cyclone, has a track
well to the south and west of the other models, while the GFS, GFS
ensemble mean, and Florida State Superensemble still show a
northward turn by day 5. Regardless, the entire guidance envelope
has shifted westward significantly after 48 hours. The NHC
official forecast has been moved in that direction, but it still
lies east of the various consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 18.7N 45.5W 35 KT 40 MPH
12H 20/1200Z 19.4N 47.2W 35 KT 40 MPH
24H 21/0000Z 20.5N 49.5W 35 KT 40 MPH
36H 21/1200Z 21.6N 52.0W 30 KT 35 MPH
48H 22/0000Z 22.6N 54.7W 30 KT 35 MPH
72H 23/0000Z 24.6N 59.1W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 24/0000Z 26.5N 62.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 25/0000Z 29.0N 63.0W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg

[Bocadude85]

0z Euro has Fiona's remains head west to Florida now.

[cycloneye]

TROPICAL STORM FIONA DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 AM AST SAT AUG 20 2016

Fiona is looking ragged this morning with only a small area of deep
convection on the northern side of the apparent center of the
cyclone. Dvorak estimates are a bit lower than earlier, but I've
elected to keep Fiona a tropical storm for this advisory given the
earlier ASCAT data, perhaps generously. The cyclone is likely to
gradually weaken for the next few days with strong shear, upper-
level convergence, and dry mid-level air in its path. After
considering the unfavorable environment ahead, the NHC intensity
forecast is reduced from the previous one, and now shows Fiona as a
remnant low in 48 hours and dissipating by day 5. This forecast
could be conservative since the ECMWF and UKMET now open up this
system into a trough within 3 days.

The initial motion estimate is about the same as before, 295/11,
mostly based on extrapolation. A subtropical ridge over the
central Atlantic should keep Fiona moving west-northwestward for
the next few days. The long-range track forecast remains highly
contingent on Fiona's status as a tropical cyclone, a remnant low,
or a trough. A deeper cyclone would likely take a more northern
turn at the end of the period due to a mid-level trough, while a
weaker cyclone would probably just continue moving to the
west-northwest (and not feel the trough). Since the cyclone is now
expected to be a more shallow system in a few days, it makes sense
to be on the western side of the guidance envelope, which requires
the new NHC track forecast to be shifted leftward beyond day 2.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0900Z 19.2N 46.7W 35 KT 40 MPH
12H 20/1800Z 20.0N 48.4W 30 KT 35 MPH
24H 21/0600Z 21.1N 50.8W 30 KT 35 MPH
36H 21/1800Z 22.1N 53.4W 30 KT 35 MPH
48H 22/0600Z 23.1N 56.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 23/0600Z 25.0N 61.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 24/0600Z 27.0N 63.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 25/0600Z...DISSIPATED

$$
Forecaster Blake

[LarryWx]

Is Fiona going to pull another Fred (of 09)?? The 6Z GFS thinks so & has her getting trapped as a weakening TC and then moving into the SE US on 9/1 as a non-TC just as Fred did.

http://weather.unisys.com/hurricane/atl ... /track.gif

[NDG]

Poor Fiona, everyone has forgotten about her. Most recent microwave pass still shows a fairly good circulation structure but definitely still suffering from SW shear & dry air from time to time.

[Ntxw]

You're right NDG she has good structure underneath. RGB loop shows it well.

[Kazmit]

You're right NDG she has good structure underneath. RGB loop shows it well.

Yeah, she is actually not looking so bad in the last few frames. Perhaps she could restrengthen after leaving the unfavorable conditions?

[northjaxpro]

Yeah Fiona is definitely a tenacious fighter that is for sure. This is highlighted especially considering the shear and dry air she has battled during the past several days.

[cycloneye]

TROPICAL STORM FIONA DISCUSSION NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
1100 AM AST SAT AUG 20 2016

Fiona is fighting off southwesterly shear this morning as the center
has become embedded under the southwestern side of an area of deep
convection. The Dvorak estimates from TAFB and SAB have held
steady, so the initial intensity is held at 35 kt. Although a
recent ASCAT overpass missed the center of Fiona, the pass did show
30-kt winds more than 50 n mi east of the center, suggesting that
tropical-storm-force winds could be occurring closer to the center
of circulation. Strong southwesterly shear of 25 to 30 kt is
forecast to persist during the next few days. These unfavorable
conditions combined with dry air along the path of the cyclone
should induce a gradual weakening trend, and Fiona is expected to
weaken to a tropical depression by tonight or early Sunday morning.
The ECMWF and UKMET models continue to open this system into a
trough within 3 days, whereas, the other model guidance lessens the
shear slightly toward the end of the 5-day period and allows Fiona
to survive for the next several days. The official forecast is
similar to the previous one, and leans toward the ECMWF and UKMET
model solutions.

The initial position of Fiona is located slightly to the north of
the previous forecast track, based on recent microwave data. The
track forecast reasoning remains unchanged, as the low- to mid-level
subtropical ridge over the central Atlantic should keep Fiona moving
west-northwestward for the next several days. There remains a fair
amount of spread in the guidance, which appears largely dependent
on the future strength and status of the cyclone. The NHC track
forecast lies on the western side of guidance, except for the short
term forecast positions where a slight adjustment to the north was
made due to the initial position and motion.

FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 20.3N 47.8W 35 KT 40 MPH
12H 21/0000Z 21.2N 49.5W 35 KT 40 MPH
24H 21/1200Z 22.3N 52.1W 30 KT 35 MPH
36H 22/0000Z 23.3N 54.8W 30 KT 35 MPH
48H 22/1200Z 24.2N 57.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 23/1200Z 26.2N 61.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 24/1200Z 28.2N 63.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 25/1200Z...DISSIPATED

$$
Forecaster Cangialosi/Latto

[Kazmit]

Fiona still "holding its strength" according to the 11am advisory from the NHC:

Fiona is fighting off southwesterly shear this morning as the center
has become embedded under the southwestern side of an area of deep
convection. The Dvorak estimates from TAFB and SAB have held
steady, so the initial intensity is held at 35 kt. Although a
recent ASCAT overpass missed the center of Fiona, the pass did show
30-kt winds more than 50 n mi east of the center, suggesting that
tropical-storm-force winds could be occurring closer to the center
of circulation. Strong southwesterly shear of 25 to 30 kt is
forecast to persist during the next few days. These unfavorable
conditions combined with dry air along the path of the cyclone
should induce a gradual weakening trend, and Fiona is expected to
weaken to a tropical depression by tonight or early Sunday morning.
The ECMWF and UKMET models continue to open this system into a
trough within 3 days, whereas, the other model guidance lessens the
shear slightly toward the end of the 5-day period and allows Fiona
to survive for the next several days.

[OuterBanker]

To be honest I thought the mlc would have detached by now with all the sw shear. Surprised that it's still hanging on. Not sure about the open wave scenario, llc looks rather healthy at the moment.