NATL: MELISSA - Aftermath - Discussion: Josh Morgerman video of Melissa is up

[Blown Away]

Melissa continues moving W of the NHC track...

[Kazmit]

CDO perfection.

[WaveBreaking]

One of the most violent CDOs I’ve ever seen, even more so than Jova’s.

[skillz305]

Just came by to say I’m praying for Jamaica.

[Hurricane2022]

One of the most violent CDOs I’ve ever seen, even more so than Jova’s.

https://i.imgur.com/rT4cxPC.gif

Even the gravity waves are becoming too violent now

[ATDoel]

One of the most violent CDOs I’ve ever seen, even more so than Jova’s.

https://i.imgur.com/rT4cxPC.gif

That inner core is nuts, looks like it's at 2x framerate.

[Michele B]

 https://x.com/NickKrasz_Wx/status/1982864599872684163

Wow. Danger on top of danger....There may be nothing left of the island after this thing passes.

[storm_in_a_teacup]

There are a lot of questions on how deep can Melissa get, or in other words what is the theoretical minimum pressure that this system can achieve. The answer is called maximum potential intensity (MPI). This is quite literally the most dangerous part of the Atlantic ocean in terms of MPI due to the sea surface temperatures (and the depth it goes to). Melissa could park over this region for days, and it would not upwell cooler waters:

https://i.imgur.com/iU4gpjr.gif

If you want to know the exact details (it's a bit of a read), but here is a post I made a while ago that outlines the mechanics of a hurricane and how to calculate MPI.

Determining the maximum wind speed a tropical cyclone can reach involves applying some thermodynamics, namely we model the mechanisms of a tropical cyclone as a Carnot heat engine (not too dissimilar from a motor/car engine). This allows us to determine the MPI (maximum potential intensity) as others have mentioned by using the Carnot cycle. But what exactly is a Carnot cycle and how does this physically look?

The Carnot cycle is characterized by four stages of expansion and compression. I created a crude diagram below to better show these stages in a cross-section of a mature hurricane:
The first stage (A→B) is isothermal expansion. In this stage, air flows inward towards the low pressure center for the storm.
The second stage (B→C) is adiabatic expansion. Air begins to rise adiabatically up the eyewall to the top of the atmosphere (TOA).
The third stage (C→D) is isothermal compression. Air now flows outward at this point and radiative cooling begins.
The fourth stage (D→A) is adiabatic compression, as air now sinks and begins to warm. Pressure increases, and the cycle begins again.

https://i.imgur.com/1UYbPBt.jpeg

Now that we can identify the inner mechanisms of a hurricane, what are we really trying to show here? First, we now know the ocean-hurricane interaction provides the fuel pump, and as a hurricane intensifies, a feedback loop begins. As wind speeds begin to increase, this also increases the evaporation rate, which in turn increases the latent heat supply that drives our Carnot engine.

Secondly, we can now apply some math equations to quantify what this value is. From our previous statement, we know our main source of latent heat/warm reservoir is our sea surface temperatures (i.e., through the evaporation process, latent heat is released). If we also treat our TOA as the outflow (think cool reservoir), we can now mathematically model a hurricane using the Carnot efficiency ratio. Skipping some of the setup using the First Law of Thermodynamics and determining work done for each leg of the cycle, we arrive at our most simplified equation:

https://i.imgur.com/ZwQOzhG.png

Where Ts is our inflow surface temperature of the ocean (hot reservoir), To is our TOA outflow temperature (cold reservoir), and E is a ratio of enthalpy and surface drag (i.e., heat exchange coefficients). In this sense, we can state the mechanical energy produced by our heat engine (V, or work done) is the energy of the winds (hurricane intensity)!

If we consider E to be constant (not the safest assumption, but will do for now), our maximum potential intensity, as stated by thermodynamics, is simply governed by the outflow temperature and the inflow temperature. In other words, this means changes in our cloud top convection or sea surface temperature strictly dictates the maximum wind speeds a tropical cyclone can reach.

With all that said, it’s important to note that we’re discussing the theoretical maximum potential intensity. Cyclones rarely reach this intensity because this requires ideal atmosphere and oceanic conditions—in other words, environmental factors rarely allow a system to reach MPI. This includes
Land interaction: this obviously removes our fuel source (latent heat release from the ocean surface)
Vertical wind shear: This causes the cyclones core to become asymmetrical, weakening the convective pattern or even creating an absence of convection on the upshear side of the cyclone (this raises our To)
Ocean interaction: As stated previously, increased wind speed can increase evaporation, but too much wind speed over a very specific area of the ocean can also cause upwelling. This localized cooling of the ocean layer decreases our Ts variable.
Dry air entrainment: If our adiabatic cooling/expansion leg of the cycle becomes disrupted by dry air, this decreases the convective potential of our cyclone and To.

She’s just having the smorgasbord of a lifetime

[aspen]

The IR (especially its last few frames) do almost look like an EWRC, although that can sometimes be deceiving.

https://i.imgur.com/4HGlter.gif

I think it’s probably another meld. Radar does still show some concentric outer bands, and the 12z HAFS models predict a meld/very brief EWRC before it unfortunately strengthens again into landfall.

If 12z HAFS are to be believed this is likely peaking right now, the meld slows it down a touch afterwards. Very easily could be <900mb, 165kts and we will have no recon to catch it until after its peaks. The current IR presentation does make the theory believable.

We probably already have enough data to extrapolate to such a peak (or something close to it). This includes:
—Pressure dropping by about 1-2mb per pass.
—FL of 160 kt, SFMR of 160-170 kt.
—Eyewall dropsondes recording 155-165 kt surface winds, including a 163 kt drop in the NE eyewall at 15:44z.
—Winds in the lower 150m of the NE eyewall averaging to 185 kt, with a 90% reduction yielding 166.5 kt.
—Extreme subsidence in the eye indicating effective transfer of winds to the surface, plus eyewall drops to support this.
—Continued lightning in the eyewall, with signs of a meld starting to show up around 18:00-18:30z.

Together, I believe this could support 903-905 mbar and 160 kt at 18z. A case could be made for 165 kt, but we probably needed another NE pass to verify those insane <150m wind measurements and just how well they’re transferring to the surface. Additionally, pressure falls looked to be slowing during the last few passes, so with the signs of a potential meld, it’s possible Melissa’s deepening has temporarily halted.

[GCANE]

 https://x.com/505Cali2/status/1982791059995349051

[Michele B]

I do think some eyewall replacement cycle is starting or occurring. The last few frames on imagery just show the CDO not as smooth as before. It would also fit in with the last eye drop just being a fraction drier. Whether it's another merger or a full cycle I'm not sure. Recon a while ago didn't show any double wind maxima so if so then it's come on rather quickly. Radar doesn't have much of a moat either so perhaps more merger than replacement.

If an EWRC of sorts is happening then could be a crucial few hours for Jamaica. Have seen it before where a little dry air or shear at just the wrong time when a storm is vulnerable mid-EWRC and it can really weaken a system. On the other hand a successful cycle and the wind field will expand, bringing some pretty populated areas within reach of stronger winds, and with ample time to strengthen further.

So not saying an EWRC is definitely happening, but certainly a change of some kind on IR imagery atm.

"When a storm is making a turn, the eye will change shape....sort of signalling the direction it's going to turn...." John Hope

[Category5Kaiju]

I'm genuinely alarmed at how well Melissa is maintaining the violent CDO and well-defined eye. By now most storms of such strength would've started to experience signs of an EWRC or weakening, but nope. Melissa seems to be an exception to that general behavioral pattern.

[Sciencerocks]

[Iceresistance]

Around 10-15 minutes ago, but look at the amount of eyewall lightning on the northwestern side

https://s12.gifyu.com/images/b3cTh.png

[Hurricane2022]

Around 10-15 minutes ago, but look at the amount of eyewall lightning on the northwestern side
https://s12.gifyu.com/images/b3cTh.png
https://s12.gifyu.com/images/b3cTh.png

The CDO is also cooling and the eye apparently shrunk a bit in the last frames. Recon is about to depart!

[ATDoel]

Around 10-15 minutes ago, but look at the amount of eyewall lightning on the northwestern side
https://s12.gifyu.com/images/b3cTh.png
https://s12.gifyu.com/images/b3cTh.png

The CDO is also cooling and the eye apparently shrunk a bit in the last frames. Recon is about to depart!

Did it shrink or is it just overshooting cloud tops? There was a decent burst right on the edge of the eyewall.

[Hurricane2022]

The stability and violence of Melissa strongly reminds me of STY Bolaven '23. Bolaven remained with a cold CDO and a very stable eye for 2 or 3 consecutive days. JTWC estimated a peak of 165 kt/897 mb for that historic typhoon.

[zzzh]

NOAA 42 taking off

[Travorum]

The NOAA recon flight is wheels up. The first fix is scheduled for 4 hours from now, but recon this morning took 3 hours to get into the storm and get the first fix and Melissa has moved a bit closer since then so we'll likely have the first eye pass from this flight between 2230-2300z if all goes well (probably towards the end of the window as Melissa isn't all that fast moving).

[Fancy1002]

Based on the data I’m seeing, Melissa seems to be repeatedly breaking new dry temperature records, just slightly.