ATL: FRANCINE - Remnants - Discussion

[Ubuntwo]

What was Francine's peak intensity?

SFMR and the Buoy Observation
During the last flight, the highest SFMR recorded to the NNE was 65kt, while the storm was still intensifying. Fortunately, the angle of this pass through the storm lines up almost perfectly with the placement of the storm vs. the buoy observation. The highest reliable SFMR overall was 75kt in the southeast quad. There was only one pass through this quadrant and it was two hours before landfall, during which the storm was intensifying. If we maintain this 75/65 ratio between NNE side surface winds/peak surface winds, the 73.8kt observation converts to a 85.2kt peak. This is making a couple big assumptions, though. Undersampling with the large RMW and SFMR alone supports 80kt.

Dropsondes
If we're looking at dropsonde data, the highest WL150m averaged wind was 96kt at 13:40z, reducing to 81.6kt. This was not on the landfall flight, though. Dropsondes on the last flight indicated mixing had deteriorated. The highest averaged 150m wind here was only 78kt, which reduces to 66.3kt. However, undersampling issues are greatly exaggerated with dropsondes. Further, only the west, east, and southeast sides had any dropsonde observations this flight. The one drop through the southeast side (where SFMR was highest) was well outside the RMW and only measured a wind of 83kt at 700mb, 700mb FL winds peaked at 99kt on that pass. This dropsonde appears to have been blown into the very edge of the eye. SFMR obs peaked earlier than FL winds all passes during the last flight, suggesting the peak wind profile was slanted outwards with height. With this consideration, the dropsondes were not properly positioned to capture peak surface winds, but do serve to confirm that winds were at least 80kt earlier in the day and that mixing was likely not the standard 90%.

Flight Level Winds
The peak 700mb flight-level wind of 106kt would typically reduce to 95.4kt at surface. However, as established above, mixing appears to have deteriorated in the leadup to landfall. With a conservative 85% reduction, this FL wind maps to 90.1kt. With a very conservative 80% reduction (same reduction used with Hurricane Zeta), this FL wind maps to 84.8kt. Because the east side was over land at landfall, the east to northeast quads could not be sampled at peak (lowest pressure), 106kt is likely an undersample. This is especially exaggerated with Francine's large RMW.

Radar Velocities
The highest 4-bin average was measured out of KHDC in the northeast quadrant around the time of landfall - 110.6kt. The peak 10-bin average was 109.5kt. This was at ~11500ft, so ~650mb. 4-bin averages hovering around 100kt were measured at the 750mb level. If we take an average of peak 650mb velocities with 750mb velocities, we get 105kt. In theory peak velocities were higher, as winds typically increase from the 650mb layer to the 750mb layer - this is conservative. Standard conversions would yield 94.5kt here, but if we apply the same conversion factor used in the Hurricane Zeta TCR (80% - the storms were quite similar in structure at landfall and baroclinic interaction), we get just about 84kt. It's worth mentioning that this was in the northeast quad, while peak flight level winds were measured in the southeast quad.

KZC Pressure Ratio
MSLP: 972mb
R34 average: 87.5nm
Translational speed: 15kt
Latitude: 29.2N
OCI: 1009mb
Output: 79.7kt

Overall
Dropsondes: 81.6kt as an absolute peak, but lower during last flight, known undersampling.
SFMR: 80kt adjusting for standard undersampling with a storm of this RMW. No SFMR at peak.
Extrapolation of highest surface observation: 85.2kt
Flight level wind reduction: 84.8kt conservatively, possible undersampling.
Radar velocities: 84kt conservatively, known undersampling.
KZC pressure ratio: 79.7kt

Overall average: 82.55kt
This is as close as it gets. Technically, this rounds to 85kt, but it's on the razor's edge. The reductions from FL and radar velocities were definitely on the conservative side (using 80%), and it might be questionable to factor dropsondes in the mix considering the massive undersampling. It's not a slam dunk downgrade, but depending on how the NHC decides to weigh SFMR, it could be reduced to 80kt in post. I think it's much more likely to remain at 85kt given their recent move back towards FL wind reductions.

[Audrey2Katrina]

You are in Metaire, which experienced only tropical storm conditions and gusts on the border between TS and Cat 1. So your account makes sense. It was not a single reading on recon. Four separate passes measured flight level winds supporting an upgrade to category 2, even if you use a more conservative reduction factor than the standard 90%. The highest offshore gust was 105 mph at a below-standard anemometer height of 4 meters. The 170mph Port Fourchon observation in Ida was highly elevated. Not saying Ida was overestimated by the NHC or anything, just making a statement about the expected obs vs. peak MSW recorded on recon, it happens in almost every storm. 3,000 obs is very impressive but not a single one was positioned in the eastern eyewall after the upgrade to category two and before or at landfall.

Where I am doesn't matter a bit. For the FOURTH time, I base my conclusions on REAL SURFACE DATA... THOUSANDS of them. My being in Metairie is utterly irrelevant.

Please provide those four flight level winds supporting Cat 2 -- because even the NHC reported them for only a span of 2 hours. I seriously doubt there were four separate passes in that time, unless you're talking of the same mission which again, I still consider only an algorithm and not an actual surface measure.

The highest offshore gust was from ONE Buoy, and the sustained winds at that SAME time were only 54kt. or 62 mph... yes offshore--same buoy, same time. Gusts don't define a storm's category. And sorry, but yes, many of those buoys WERE in the eastern eyewall after the upgrade to category 2 and most definitely before and at landfall.. that's why I have so many. I can still respect your going along with the NHC's algorithm, kindly don't assume so much on my observations as I've done this for decades.

A2K

[Audrey2Katrina]

What was Francine's peak intensity?--- Cat 1... and I'm sticking with that.

[Ubuntwo]

You are in Metaire, which experienced only tropical storm conditions and gusts on the border between TS and Cat 1. So your account makes sense. It was not a single reading on recon. Four separate passes measured flight level winds supporting an upgrade to category 2, even if you use a more conservative reduction factor than the standard 90%. The highest offshore gust was 105 mph at a below-standard anemometer height of 4 meters. The 170mph Port Fourchon observation in Ida was highly elevated. Not saying Ida was overestimated by the NHC or anything, just making a statement about the expected obs vs. peak MSW recorded on recon, it happens in almost every storm. 3,000 obs is very impressive but not a single one was positioned in the eastern eyewall after the upgrade to category two and before or at landfall.

Where I am doesn't matter a bit. For the FOURTH time, I base my conclusions on REAL SURFACE DATA... THOUSANDS of them. My being in Metairie is utterly irrelevant.

Please provide those four flight level winds supporting Cat 2 -- because even the NHC reported them for only a span of 2 hours. I seriously doubt there were four separate passes in that time, unless you're talking of the same mission which again, I still consider only an algorithm and not an actual surface measure.

The highest offshore gust was from ONE Buoy, and the sustained winds at that SAME time were only 54kt. or 62 mph... yes offshore--same buoy, same time. Gusts don't define a storm's category. And sorry, but yes, many of those buoys WERE in the eastern eyewall after the upgrade to category 2 and most definitely before and at landfall.. that's why I have so many. I can still respect your going along with the NHC's algorithm, kindly don't assume so much on my observations as I've done this for decades.

A2K

Look above, I conclude based on all data that it was as close to borderline cat 1/cat 2 as it gets. It could go either way.

I mapped the area of category 2-equivalent FL winds and there were no buoys directly in that swath (see below). Yes, the 91kt gust was coupled with tropical-storm-force winds, BUT the same buoy recorded 74kt sustained earlier in the north eyewall. Here are four separate FL observations, four separate passes, supporting category 2:
106kt @ 22:13z, southeast quad (indirect pass)
102kt @ 21:32z, east-southeast side
96kt @ 20:55z, east-southeast side
99kt @ 20:16z, southeast side

You're right, the reduction is not perfect. Dropsondes indicated below-normal mixing, similar to Zeta. This is why I use a reduction of 80% or 85% instead of 90% - even with 80%, FL winds alone do support a very low end category 2.

Map of buoys coupled with swath encompassing all of the above observations. Yes, the swath was that tiny.
The yellow spot to the northwest of the swath recorded 74kt, flight level winds were lower in this region of the eyewall. The red buoys were not reporting yesterday either.

I could very easily be missing some observations. If there are any in that area, let me know, it would make the case for 80kt much much stronger.

[Stormcenter]

I don't get the obssession with what the peak intensity was with Francine. That is a mute point to those who are currently without
power and dealing with damage or flooding associated with the storm. To those people it doesn't make one bit of difference and it doesn't make
it any better if it was a cat. 1 or 2. Just my two cents.

[Ubuntwo]

I don't get the obssession with what the peak intensity was with Francine. That is a mute point to those who are currently without
power and dealing with damage or flooding associated with the storm. To those people it doesn't make one bit of difference and it doesn't make
it any better if it was a cat. 1 or 2. Just my two cents.

Absolutely. It's 5 knots either way and if it was a two, nobody except the birds saw those winds. No disrespect to those dealing with the storm. But I think it is an interesting meteorological discussion to have, and this is a weather forum after all. After any big storm there will naturally be some back-and-forth as we try and figure out exactly what the landfall/peak intensity was.

[tolakram]

I agree, there's nothing more to discuss. We'll see what get's decided when everything is reanalyzed after the end of the season.

[Ubuntwo]

Long radar loop of Francine:


Landfall:

[Tailgater33]

A couple things real quick. I just got power back, I don’t care wether it’s a 1 or 2, I wish they would drop that designation myself. I don’t care if it is sustained winds or gust. Gust winds damage too. I realize the need label a storm this or that but it only tells a minute part of the storm’s destruction capabilities. Size of wind field, size of eyewall, speed, angle of impact, tornado threat, flood threat and so many more.
Where are those motorized buoys?

[Audrey2Katrina]

I agree, there's nothing more to discuss. We'll see what get's decided when everything is reanalyzed after the end of the season.

I know you meant about the category. (I still say a 1 ) But lots more can be discussed about how the southern half literally disappeared as it moved inland. Was it dry air entrainment? I find it fascinating how this has happened now on a couple of storms hitting the northern Gulf. Bizarre. As for the poor souls dealing with power outages and water, trust me. I feel you! Flooded three times, twice quite seriously. Power out for weeks from both Katrina and Ida, -- oh yeah, and Betsy. Been there done that, and I agree it's not fun, although I confess as a teen during Betsy, it was a bit of an adventure to me--Mom and Dad felt otherwise.

Bottom line is it doesn't even take a hurricane to be a tragedy that some people will never recover from. I forgot the name, but at least 8 or 10 years ago, a tropical storm struck Florida's panhandle-- only one death as I recall was recorded, a child I think living in a trailer. I believe it was from a tree blown over. I wrote a tribute for the family--no storm is something to take for granted, and some of the weakest can become the most horrific if it affects YOU, or someone you love. Tropical Storm Allison dumped FEET of rain in areas of Texas putting it well up on the list of all storms for damage. If your house is flooded with several feet of water, and you lose countless pictures, or worse, a family member, no TV, appliance, car, roof, or what have you will ever replace those memories, of loved ones. I still feel for those folks who lost a child in a tropical storm. NEVER make light of these monsters. This is why I don't join in with many who get all excited when a storm blows up into a major threatening to make landfall, because I've been through too many of them. I chalk it up to youth and just the awe of nature's power... but, having seen over a hundred of these things in my long years, I think of lives that will be lost, whole families that will wind up without a roof over their heads, for those who will have their life savings wiped out in one horrific day or night; and I pray for any affected, and pray strongly that it doesn't come my way. Only the fact that my family has lived here since the early 1700's (and my age now), keeps me here. God bless all, and please... stay safe!

A2K

[kassi]

I could be wrong as it's still early, but based on reports I've seen, it seems like cat. 1 Beryl was far more destructive than cat. 2 Francine.

I chased both. Strictly speaking for wind, I'd say they packed about the same punch. Similar levels of structure damage, but I'd give the edge to Francine. What I found very interesting was how Francine's western eyewall was solidly more intense than the eastern. I caught it first in Houma and thought "Okay, that felt like a Solid Cat 1, no back side to it so might as well catch the western part on the way out." It surprised me compared to the east, that band of northerlies was absolutely ripping. Lots of trees down.

I didn't chase either. I was just going by reports. 28-32 billion damage with Beryl as opposed to 9 billion in damage with Francine. 36 deaths attributed to Beryl. None to Francine thankfully! Over 3 million without power with Beryl , some lasting weeks. Over 400,000 without power with Francine, almost all already restored.

[Travorum]

SAR product generation was down while Francine was actually active but now that it is back they uploaded a couple interesting acquisitions. The sequential captures show the evolution of the core structure from the initial compact core that was interrupted by dry air intrusion to the much broader core that subsequently developed. Additionally, if the Vmax of each capture is correct, these suggest that the NHC was pretty much spot on with intensity estimates from at least 9/10 to 9/11.

	⠀⠀⠀		⠀⠀⠀
Platform: RCM-1 Acquisition Date: 2024-09-10 00:30:21 UTC Storm Name: AL062024 / FRANCINE Storm ID: AL06 Storm Center Longitude: -96.035 Storm Center Latitude: 23.923 Incidence Angle (Degrees): 43.806 Quadrant 1 NE VMax (kts): 39.87 Quadrant 2 SE VMax (kts): 55.07 Quadrant 3 SW VMax (kts): 51.88 Quadrant 4 NW VMax (kts): 52.66 RMax (nmi): 11.00 - 43.00	⠀⠀⠀	Platform: RCM-1 Acquisition Date: 2024-09-10 12:22:14 UTC Storm Name: AL062024 / FRANCINE Storm ID: AL06 Storm Center Longitude: -95.690 Storm Center Latitude: 24.520 Incidence Angle (Degrees): 34.930 Quadrant 1 NE VMax (kts): 56.57 Quadrant 2 SE VMax (kts): 56.65 Quadrant 3 SW VMax (kts): 46.54 Quadrant 4 NW VMax (kts): 52.11 RMax (nmi): 9.00 - 16.00	⠀⠀⠀	Platform: RCM-2 Acquisition Date: 2024-09-11 11:57:34 UTC Storm Name: AL062024 / FRANCINE Storm ID: AL06 Storm Center Longitude: -93.182 Storm Center Latitude: 27.458 Incidence Angle (Degrees): 58.697 Quadrant 1 NE VMax (kts): 72.21 Quadrant 2 SE VMax (kts): 80.66 Quadrant 3 SW VMax (kts): 76.39 Quadrant 4 NW VMax (kts): 64.25 RMax (nmi): 21.00 - 28.00

[LARanger]

Long radar loop of Francine:
https://i.imgur.com/GXaRcgU.gif

Yeah, this loop bothers me.

Can anyone explain how they concluded that there should be a center fix over Lake Maurepas? I don't see any indication of that in the loop, so I presume I'm missing something. As noted, many of the publicly visible models had this going swimming in Lake Ponchartrain for multiple runs, though the NHC had it projected to hit Baton Rouge almost to landfall.



On the good side, the Maurepas fix should up the accuracy score a bit, being within 5 miles of the centerline of the previous prediction. I realize forecast track line usage is naughty and the Maurepas fix versus following a path to Ponchartrain is like a 15 mile difference on a Category (cough) storm that had something like a 40 mile wide eye. That is to say, the whole thing isn't that important in the grand scheme of things. However, using my I-12 metric, the result was a 40 mile difference, which is meaningful.

Clearly I'm missing something.

[AJC3]

Long radar loop of Francine:
https://i.imgur.com/GXaRcgU.gif

Yeah, this loop bothers me.

Can anyone explain how they concluded that there should be a center fix over Lake Maurepas? I don't see any indication of that in the loop, so I presume I'm missing something. As noted, many of the publicly visible models had this going swimming in Lake Ponchartrain for multiple runs, though the NHC had it projected to hit Baton Rouge almost to landfall.

[url]https://i.ibb.co/Jj2xwtw/image-2024-09-16-223926148.png [/url]

On the good side, the Maurepas fix should up the accuracy score a bit, being within 5 miles of the centerline of the previous prediction. I realize forecast track line usage is naughty and the Maurepas fix versus following a path to Ponchartrain is like a 15 mile difference on a Category (cough) storm that had something like a 40 mile wide eye. That is to say, the whole thing isn't that important in the grand scheme of things. However, using my I-12 metric, the result was a 40 mile difference, which is meaningful.

Clearly I'm missing something.

We were looking at an increasingly tilted/disorganized system at/after landfall due to increasing WSW to W shear. If you focus on the west side, there does appear to be a small concavity in the echoes that looks like it moved across Lake Maurepas, while what was left of the mid-upper level circulations (purple-mauve), moved across Lake P.



Having not looked at any surface and mesonet observations, that would be my best guess as to what the NHC might have seen. Plus, of course, the best track is always subject to revisions. In the end, close examination of the wind/pressure observations will give a much better series of post-landfall center fixes.

[LARanger]

I didn't take tilt and different assessment by altitude into consideration, so would need to review even the various Pontchartrain-pointing models I was looking at prior to landfall to see if that has explanatory power. Thanks for that!