ATL: SAM - Remnants - Discussion

[Fancy1001]

Once again the hunters miss it at its peak strength

[Yellow Evan]

18L SAM 210927 0000 14.5N 50.6W ATL 130 940

Nothing supports 130.

[TorSkk]

T6.5 estimates with Sam were probably low because of how hard it is for Atlantic cyclones to get a "true" T7 (outside of deep Carribean like Eta). It's somewhat random whether the CDO is smooth W or there are spots of B when they do the fix

[Yellow Evan]

 https://twitter.com/mesovorthunter/status/1442292383752855552




Screams drawn out ERC since inner eyewall is clearly fighting.

[skyline385]

I think we should be grateful that we even have recon going that far out and braving storms out just for scientific data. Sam is not even a danger to anyone so they dont even have much reason to risk themselves yet there they are.

Think a lot of people need some perspective, missing peak strength on a Cat 4/5 storm going OTS isnt the end of the world and probably is on the lowest priority for the NHC, just be thankful that we atleast have some recon...

[Stormybajan]

 https://twitter.com/webberweather/status/1442293710788513792



Sam in a nutshell.

[aspen]

I hope they mention the 929mb drop in the 11pm discussion, just like they mentioned the 929mb drop for Ida after a later drop found 933mb.

[Sciencerocks]

[Yellow Evan]

 https://twitter.com/andyhazelton/status/1442313601436446722

[Teban54]

That was some extremely rapid weakening. As much as we all agree that recon was too late, it could have been a lot worse.

[TheAustinMan]

The maximum brightness temperature recorded by satellite in the infrared is often correlated with storm intensity, which is why for example it has a place in Dvorak. Generally, the warmer the eye, the stronger the system, and we've seen this with both satellite data and the actual temperatures that reconnaissance missions observe when they fly into hurricane eyes. Looking at a plot of brightness temperatures in two bands (band 14, the conventional longwave IR band; band 10, the low-level WV band), we can see that Hurricane Sam maintained a remarkably warm eye that held rather consistently in central temperature during the early afternoon, with the warmest temperatures occurring around 18 UTC.

While the setting sun has some influence on temperatures, the high heat capacity of the ocean tells us that most of these temperature changes will be driven by the storm's actual structure and by extension intensity. We see that beginning around 20 UTC, there was some onset of fluctuating temperatures in the eye, which escalated further to a very strong cooling trend after 22 UTC as Sam's structure began to quickly unravel. Unfortunately, recon did not make it into Sam until after this downtrend had begun in earnest, but still managed to record a 932 mb pressure with a dropsonde on its first pass (which roughly corresponds to 929 mb when accounting for the lack of relative calm observed at the surface). When the recon flew back into the center on its second pass, the next dropsonde recorded a much higher pressure, equating to about 941 mb, as the storm's eye continued to cool drastically.

One can probably infer that Sam was stronger and deeper than what recon observed on its first pass based on the observed trends. While temperatures do not relate exactly to intensity numerically, if we apply a 3C/mb relationship to band 14 based on the weakening observed between the first two recon passes, we might guesstimate that Sam had a pressure in the low- to mid-920 millibars during the early afternoon before the onset of weakening. Given Sam's size and location, such pressures would correspond to a 140 or 145 kt Category 5 hurricane. It is my personal judgement that Sam reached such an intensity earlier today, when lightning activity fully encompassed the eyewall within a very smooth and astonishingly symmetric central dense overcast.

41.2 KB. Data collected using the AWIPS CAVE program.

[RL3AO]

A NOAA Hurricane Hunter aircraft investigating Sam this afternoon
and evening found that the major hurricane likely peaked in
intensity at around 135 kt with a central pressure of about 929 mb
between 1900-2200 UTC when the eye contracted down to about 7 nmi in
diameter.

[NotoSans]

Latest discussion says Sam likely peaks at 135kt between 19Z and 22Z.

[Stormybajan]

A NOAA Hurricane Hunter aircraft investigating Sam this afternoon
and evening found that the major hurricane likely peaked in
intensity at around 135 kt with a central pressure of about 929 mb
between 1900-2200 UTC when the eye contracted down to about 7 nmi in
diameter.

155 mph 929mb peak, much better. How right now im wondering if Sam can even recover from what ever is causing this rapid weakening.

[Category5Kaiju]

155/929? Yeah that seems much more plausible for peak strength than 150/938. Sam looked way too good for that.

[WiscoWx02]

Eye is almost gone on satellite, convection has eroded. I think Sam is about to kiss goodbye to major hurricane intensity.

[Teban54]

A NOAA Hurricane Hunter aircraft investigating Sam this afternoon
and evening found that the major hurricane likely peaked in
intensity at around 135 kt with a central pressure of about 929 mb
between 1900-2200 UTC when the eye contracted down to about 7 nmi in
diameter.

Given that Sam had clearly started weakening when the 929 mb pressure was recorded (as seen from the excellent plot by TheAustinMan), I think there's a pretty good chance its actual peak was stronger than 135/929, based on the assumption that pressure was rising at the time of the first recon pass. At this point it's basically a coin flip whether it did reach 140 kt.

In the past, they extrapolated lowest pressure between recons for Patricia, but not for Eta (IIRC).

[Category5Kaiju]

Assuming the pressure stayed at 929 mbar, the question of 155 mph vs 160 mph becomes a bit foggy; however, perhaps we could look at the structure of Emily 2005 as her peak was 160/929 but was initially a 155/929 peak for reference to what Sam *could* have been?

[ElectricStorm]

I like the 135kt peak estimate, I think there was a solid chance it peaked at 140kts but without any solid evidence of that, I think 135 is a good call.

As for the current intensity IMO this is nowhere near 125kts. It looks like it's getting slammed by shear and undergoing an ERC at the same time. I would probably go with 100kts at the max, although that might be generous. If this continues we could be looking at one of the all-time weakening rates. Sam still has a long life ahead, so I would think it could have a chance to get going again in a few days but it's not looking good at all right now.

[DestinHurricane]

This could have the most ACE since Irma?