NATL: MELISSA - Hurricane - Discussion

[USTropics]

That large band with deep convection to the east is interesting. Must be the “Matthew effect” from being in a similar location at a similar time of year, lol.

Could that huge eastern blob of convection hindering the intensification? it appears too "heavy" for small Melissa to carry - like it's dragging the whole circulation not to spin faster.

sort of like a spinning top with uneven weight.

There are very intense storms that had strong spiral bands but their bands look "smooth". Melissa's doesn't look smooth at all

I've done a lot of research in this area, and it's definitely unique to this region like you stated. This all due to how the circulation around Melissa interacts with the prevailing easterly flow at this latitude and essentially establishes this convergence zone, or 'blob of convection' to the east of Melissa. Specifically, this is what is occurring:

1) There is a stationary band complex east of the system, or essentially confluence downshear (i.e., downshear direction is the southeast and northeast quadrant in this instance)
2) There is a surge in trade winds (see images below) coming from east -> west that interacts with this
3) We also have confluence downstream due to the vicinity of landmasses/terrain
4) Finally we have asymmetries due to mixing of drier air and these moist boundary layers

We can best see this by how the flow is completely different based on the level of the atmosphere we are in (and it doesn't impact intensity):

Surface (trade winds)


Mid levels (700mb)


Upper levels (500mb)


Near Troposphere (250mb)

[tulum07]

Is the blob to the East going to follow Melissa at a short distance or will Melissa absorb it? It looks very impressive .

[USTropics]

Is the blob to the East going to follow Melissa at a short distance or will Melissa absorb it? It looks very impressive .

Until Melissa starts to move north and away from the trade wind surge, I'd expect it to be a semi-permanent feature. This is likely to get dragged up into Hispaniola at some point and exacerbate flooding there.

[MEANINGLESS_NUMBERS]

I know Jamaica has much bigger problems but Bermuda in the cone for the 6th time this season.

[USTropics]

I want to dispel this thought that a cat 5 requires a pinhole eye. It does not. There is a lot that goes into hurricane dynamics besides the size of the eye
https://upload.wikimedia.org/wikipedia/commons/6/6e/Isabel_2003-09-14_1245Z.jpg
https://media.npr.org/assets/img/2018/06/15/gettyimages-843792064_wide-40ed851f4958605f65f2974df45011df5941106c.jpg

That was never implied, but rather when explosive bouts of RI occurs it is very common that pinhole eyes are present, especially for storms of Melissa's size.

Latitude plays a critical role here, remember we have additional forces to consider (e.g., centrifugal and Coriolis) when we are dealing with radial winds. The analogy is simple here: ice skater pulls arms in -> spins faster; ice skater extends arms out -> decelerates. If the ice rink is spinning faster with the ice skater (i.e., increase latitude -> increase Coriolis -> increase environment vorticity) it's easier to achieve without 'pulling our arms in more'.

[Kazmit]

I know Jamaica has much bigger problems but Bermuda in the cone for the 6th time this season.

Will probably be another nonevent like Imelda. Moving quick and probably a minimal hurricane by then. Maybe a direct hit of the eastern eyewall would be problematic.

[cheezyWXguy]

That large band with deep convection to the east is interesting. Must be the “Matthew effect” from being in a similar location at a similar time of year, lol.

Could that huge eastern blob of convection hindering the intensification? it appears too "heavy" for small Melissa to carry - like it's dragging the whole circulation not to spin faster.

sort of like a spinning top with uneven weight.

There are very intense storms that had strong spiral bands but their bands look "smooth". Melissa's doesn't look smooth at all

I've done a lot of research in this area, and it's definitely unique to this region like you stated. This all due to how the circulation around Melissa interacts with the prevailing easterly flow at this latitude and essentially establishes this convergence zone, or 'blob of convection' to the east of Melissa. Specifically, this is what is occurring:

1) There is a stationary band complex east of the system, or essentially confluence downshear (i.e., downshear direction is the southeast and northeast quadrant in this instance)
2) There is a surge in trade winds (see images below) coming from east -> west that interacts with this
3) We also have confluence downstream due to the vicinity of landmasses/terrain
4) Finally we have asymmetries due to mixing of drier air and these moist boundary layers

We can best see this by how the flow is completely different based on the level of the atmosphere we are in (and it doesn't impact intensity):

Surface (trade winds)
https://i.imgur.com/dDX27yf.png

Mid levels (700mb)
https://i.imgur.com/tQqTfCq.png

Upper levels (500mb)
https://i.imgur.com/mopPiDz.png

Near Troposphere (250mb)
https://i.imgur.com/xGsP9qV.png

It’s number 4 on your list that I’m suspecting to be the biggest culprit at the moment, although I’m sure it’s a combination of all like you said. Dropsondes from the southeastern half of the storm appear to be less saturated through the measured portion of the column than those from the northwestern half. Each time a band like this appeared the intensity leveled off, and after it weakened a new phase of intensification followed immediately after, which also lends credence to 1900hurricane’s lobing argument. When present, this feature seems to compete with the core for energy in some way.

[MEANINGLESS_NUMBERS]

I know Jamaica has much bigger problems but Bermuda in the cone for the 6th time this season.

Will probably be another nonevent like Imelda. Moving quick and probably a minimal hurricane by then. Maybe a direct hit of the eastern eyewall would be problematic.

Yes, even the worst case scenario for us will be very brief duration winds. And Imelda already cleared the vulnerable trees.

[Teban54]

I could be reading too much into this, but...

A new burst of eyewall convection just appeared, immediately next to the "dry air channel" and near the convective blob. It's the strongest that I recall seeing this morning.

Could this be an attempt at shielding off the dry air and reintensifying?

[LarryWx]

You can tell that the NHC has an extra tough challenge right now considering it’s 10:57AM EDT and the 11AM just came out. It usually comes out by 10:45AM.

[USTropics]

Could that huge eastern blob of convection hindering the intensification? it appears too "heavy" for small Melissa to carry - like it's dragging the whole circulation not to spin faster.

sort of like a spinning top with uneven weight.

There are very intense storms that had strong spiral bands but their bands look "smooth". Melissa's doesn't look smooth at all

I've done a lot of research in this area, and it's definitely unique to this region like you stated. This all due to how the circulation around Melissa interacts with the prevailing easterly flow at this latitude and essentially establishes this convergence zone, or 'blob of convection' to the east of Melissa. Specifically, this is what is occurring:

1) There is a stationary band complex east of the system, or essentially confluence downshear (i.e., downshear direction is the southeast and northeast quadrant in this instance)
2) There is a surge in trade winds (see images below) coming from east -> west that interacts with this
3) We also have confluence downstream due to the vicinity of landmasses/terrain
4) Finally we have asymmetries due to mixing of drier air and these moist boundary layers

We can best see this by how the flow is completely different based on the level of the atmosphere we are in (and it doesn't impact intensity):

Surface (trade winds)
https://i.imgur.com/dDX27yf.png

Mid levels (700mb)
https://i.imgur.com/tQqTfCq.png

Upper levels (500mb)
https://i.imgur.com/mopPiDz.png

Near Troposphere (250mb)
https://i.imgur.com/xGsP9qV.png

It’s number 4 on your list that I’m suspecting to be the biggest culprit at the moment, although I’m sure it’s a combination of all like you said. Dropsondes from the southeastern half of the storm appear to be less saturated through the measured portion of the column than those from the northwestern half. Each time a band like this appeared the intensity leveled off, and after it weakened a new phase of intensification followed immediately after, which also lends credence to 1900hurricane’s lobing argument. When present, this feature seems to compete with the core for energy in some way.

I'm actually excited someone pointed out #4 (it's the least well known and researched factor here), and I do think it plays a critical role. Like most things in meteorology, there is a 'total budget' and we have to identify each contributing factor. I would be hesitant to say this is weakening the system (we went cat1 -> cat4 in like 12-14 hours afterall), but it definitely could limit moisture fluxes and create a temporary leveling off to intensity..

[USTropics]

I could be reading too much into this, but...

A new burst of eyewall convection just appeared, immediately next to the "dry air channel" and near the convective blob. It's the strongest that I recall seeing this morning.

Could this be an attempt at shielding off the dry air and reintensifying?

https://i.imgur.com/05iLUyU.gif

This is essentially a rinse and repeat of what occurred yesterday (quoted my post below, minus red VHT), and what I would expect to see occur today before/if Melissa begins another phase of RI. Like I was stating earlier, there have been concentric features on radar (and forecasted by HAFS-A) and this has created this eyewall melding scenario + some undercutting shear. It's prevented the eyewall from really contracting and is what has caused the level-off in intensity today imo.

I think Melissa has gotten the dual VHTs, the arrows are direction. The northern VHT is moving fast
https://s12.gifyu.com/images/b3n30.png
https://s12.gifyu.com/images/b3n30.png

Definitely some VHTs induced by the dry air interaction with the moist profile of Melissa's improving inner core:


We have some dry air entrainment as Melissa starts to expand her convective envelope. Meanwhile, we have this moist inner core developing which has high equivalent potential temperature (PT). This creates these localized boundaries where inflow basically hits a wall, and we get enhanced convergence when the dry air hits the moist inflow (environment PT decreases, parcel buoyancy increases), and rapid ascent of warm, moist air takes place (our VHTs).

Each point where the dry air "hits" the moist core can initiate a separate updraft. The red VHT is optimally positioned so it has the largest vertical ascent initially. As teal continues to rotate towards the north, it gets more of those direct localized enhanced convergence effects. This is the response to balance two things: (1) the asymmetric structure that Melissa currently exhibits and (2) as a means to mix out the dry air intrusion before it reaches the inner core and disrupts the eyewall formation cycle.

https://i.imgur.com/zxBei8V.gif

[syfr]

You can tell that the NHC has an extra tough challenge right now considering it’s 10:57AM EDT and the 11AM just came out. It usually comes out by 10:45AM.

I noticed the 30+ inches of rainfall on sections of Cuba.

Three FEET of rain is incredible to consider.

[cheezyWXguy]

I could be reading too much into this, but...

A new burst of eyewall convection just appeared, immediately next to the "dry air channel" and near the convective blob. It's the strongest that I recall seeing this morning.

Could this be an attempt at shielding off the dry air and reintensifying?

https://i.imgur.com/05iLUyU.gif

I think this is true. Yesterday when this occurred, it seemed to follow this order of events:
1- prominent band forms, initially as a discrete blob, near the periphery of the cdo. Intensification levels off.
2- blob stretches into more of a classic band appearance, a moat between this band and the cdo becomes apparent.
3- new cells appear in the moat, eventually filling in as the original prominent band is gradually pushed farther away from the cdo and begins to lose influence.
4- new bursts begin to appear in the cdo/eyewall as the prominent band continues to weaken.
5- intensification resumes as eyewall bursts become stronger and band weakens further/dissipates.
If this is a repeatable sequence of events for today, I think we’re at the 4th point by now. We should watch to see if the band gets further removed from the core, new banding forms in the dry moat, and if new bursts continue to occur in the eyewall over the next couple hours.

[kevin]

While the CDO is degrading on the NW side, a new strong burst of convection is wrapping around counter-clockwise from the previously weaker eastern side. If it fully wrapps around the CDO we could see continued intensification. Luckily, there's another recon plane nearing Melissa so we'll know all the details about her current state very soon.

[aspen]

I know we basically said this about last flight but this is a good time for recon to be heading in. Melissa seems to be picking back up after whatever halted its RI this morning. I wonder how much longer we’ll see this stair-stepping intensification.

[Teban54]

I could be reading too much into this, but...

A new burst of eyewall convection just appeared, immediately next to the "dry air channel" and near the convective blob. It's the strongest that I recall seeing this morning.

Could this be an attempt at shielding off the dry air and reintensifying?

https://i.imgur.com/05iLUyU.gif

I think this is true. Yesterday when this occurred, it seemed to follow this order of events:
1- prominent band forms, initially as a discrete blob, near the periphery of the cdo. Intensification levels off.
2- blob stretches into more of a classic band appearance, a moat between this band and the cdo becomes apparent.
3- new cells appear in the moat, eventually filling in as the original prominent band is gradually pushed farther away from the cdo and begins to lose influence.
4- new bursts begin to appear in the cdo/eyewall as the prominent band continues to weaken.
5- intensification resumes as eyewall bursts become stronger and band weakens further/dissipates.
If this is a repeatable sequence of events for today, I think we’re at the 4th point by now. We should watch to see if the band gets further removed from the core, new banding forms in the dry moat, and if new bursts continue to occur in the eyewall over the next couple hours.

I think you're onto something. From the loop below, you can also see the new burst attempting to quickly turn itself into the new CDO (which has wrapped around 70% of the eyewall since the last frame of the loop). The blob is also showing clear separation from the core: Melissa's center has been slowly drifting W, while the blob remained somewhat stationary.



This is quite similar to the huge burst yesterday that kickstarted the ERI (the loop here shows the whole process). For reference, the start of this loop was exactly when USTropics wrote the detailed explanation, which was quoted again upthread.

The main differences I see are:

• When the burst happened yesterday, the nearby blob has already greatly weakened. (You can see initial stages of that blob here a few hours earlier.) Right now, however, the SE quad of the blog is still quite active even when the new burst is already wrapping around.
• This process yesterday happened when Melissa was still a minimal hurricane. Since it's at a much higher intensity now, EWRC (or at least eyewall melds) may complicate things.

[Teban54]

A more up-to-date loop showing the latest burst almost wrapping around in full:

[kevin]

Compared to Milton or Wilma it might 'feel' like Melissa isn't intensifying nearly as fast and has more periods of constant intensity. And while it is true that this won't break the TS -> C5 record time, she still went from a 60 kt TS to a 120 kt C4 within the last 24 hours. The fact that we already knew that Melissa would bomb out long in advance also makes it feel like it's just taking a long time. But Melissa's RI is still extremely impressive.

And much more worringly, Melissa still has about 44 hours left until landfall according to the NHC (or up to 48 - 52 hours if HAFS-A/B are correct). Things don't need to line up perfectly (as is often the case for these worst-case scenarios) for a historic and extremely damaging landfall in Jamaica: it still has time for multiple EWRCs and then another RI phase into a C5 before landfall. I'm afraid this is gonna be Jamaica's 'big one'.

[Hypercane_Kyle]

There may be another intensification burst... eye is looking more symmetrical with deep convection wrapping around again.