Moderately Unstable

Eta is strengthening. While I tend to be on the more bullish side when it comes to intensity forecasts, the following factors are useful to know: -Current SSTs under Eta 29C. -Current shear: 10-15 knots. Shear forecast: 5-15 knots. Shear tendency: -5kts/24hrs. -Current regional SST anomaly: +0.5-1C. -Current OHC: 100-125 kJ/cm^2. -Current maximum potential TS intensity based on OHC: Category 5/900-910mb. -Upper level anticyclone ESE of CoC. -MJO: Phase 5. -Current steering winds take the storm over land in the 48hr time frame. // Objective: -Current microwave data suggests a core is forming. // Analysis (Subjective): -OHC is decent but not off the charts. -Wind shear is low. -Visible & IR sat imagery indicate the system is quickly organizing. It will run out of ocean in slightly less than 2 days. The probability of attaining maximal potential intensity is reduced by this factor. Achieving major status seems plausible but not certain. If hurricane hunters find a massive jump in winds to 65-70 a major is more likely. I base this educated guess on the satellite presentation, intuition, and past storms, more than I do the intensity guidance. -SHIPs is bullish on potential for RI; SHIPs is often bullish so, I find it notable, but don't want to cherrypick data. -It appears to currently be strengthening rapidly, and I expect hurricane hunters to report that. The band to the west in particular was notable to me in being a hallmark of past strong hurricanes and strengthening systems. -It will be strengthening as it hits the coast regardless of intensity, thereby increasing wind hazards. Mountainous terrain will enhance gusts as well. Less prosperous nations such as Honduras and Nicaragua face an outsized risk from landfalling hurricanes due to on average less robust infrastructure and building materials.

You have a *strong* track record this season in terms of forecasting, so I don't think you should discount your input as nonsense. We are ALL looking at the same data which doesn't all agree and trying to figure out what to believe and what factors support our thinking. You have a high likelihood of being right on models changing and missing something by shear nature of the way hurricanes and models work. Short time frame models tend to have a good handle on what will happen. Longer term they aren't. That's always how it works. This is where analogs, the large scale pattern, model performance in given large scale patterns (too progressive too slow over enthusiastic) come into play. My memory is that with a few exceptions with very clear data, the nhc doesn't project a major hurricane often when any storm first forms. If conditions are favorable, a hurricane is forecast in the 5 day range. There are exceptions. Hence the fact they don't numerically predict a strong hurricane in their forecast doesn't mean that won't happen, and they state as much in their discussion. In summary--you aren't being paid for your opinions on here so no need to bash them. It's a weather forum. Right or wrong you learn something, and you aren't auditioning for a job. I've been here for 3 months and I feel more confident in posting now for that reason; if I'm saying something nonsensical someone will say something or gloss past my post entirely and I learn from that. From a statistical perspective, this part of the Caribbean is the locus for intensifying tropical systems at this time of year. Take that fwiw.

My thoughts are likely that they needed some type of objective measurement (e.g. ASCAT) which missed the system several times in a row. Without objective data, they can't truly determine if (a) the circulation was elongated or tightly closed, (b) the intensity of the storm. Since it's been clear for perhaps 48 hours now that this storm would eventually form a surface circulation and the time frame in which the system really poses a land and life threat is a few days out, they probably felt it prudent to wait for objective data to both better make a forecast, improve model predictability, and provide a better starting intensity. A minor but present issue--lets say they initiated and subjectively went with 30mph winds. But then, objective data came in and showed 3 hours later the storm was at 50mph. Over the following 24 hours, the storm RIs into a 100mph monster. One could then infer the storm was on pace to become a cat 5 monster. If instead the first advisory sampled 50 mph winds (making it a ts), then that rise, while substantial, isn't quite as "wilma-esq". In addition, weak and developing systems are less stable than stronger ones. Some unknown shear or dry air or what have you could weaken the storm or change the position of the surface low by a large distance. It boils down to--what data can objectively prove a closed low? I'd bet money that if ASCAT had provided data this am, they'd have classified it this morning. The sat presentation at this point, in my subjective opinion, is too strong to ignore even in absence of more objective measurements.

The nhc has announced they will initiate advisories on TD 29 at 5pm.

Looking at visible sat, they have to classify this thing soon. They're looking for a closed, low-level, non-elongated circulation... I have a hard time believing a storm could have that current structure on visible and lack such a circulation. Based on the ensembles, it looks like none of the pertubations think it won't head west towards Central America. The medium term has a few possibilities for curving north and northeast and hit Florida via Cuba. The suite of hurricane specific track models is also fairly consistent with an initial westward track. Looking at the upper level progs, it appears the reason for the directional shift is a Mexican surface low coupled with a departing deep trough over the southern US and something I don't have a handle on to the SE of what will likely by then be Eta.Those two things change the steering currents according to the gfs and draw the storm north. The issue with the gfs right now is it's relatively slow to strengthen and organize the storm. Most of the other guidance has it getting stronger more quickly. I think the bulk of the hurricane specific guidance RIs the storm, and then assumes that if so, it should slam into Central America. There's a secondary possibility of a glancing blow to Central America and then a turn north supported by a few ensemble members. What's important is that this storm is organizing quickly, and that is more in line with HMON/HWRF than either the gfs or the other hurricane track models. So, I suspect that the global guidance will shift dramatically when the low consolidates and hence steering based on that can be better defined. At the rate it's going its going to be a hurricane when it gets classified!

Hm. 29 degree SSTs, well developed convection, 10 knots of shear relaxing by Monday morning, dynamical and statistical models bullish and in agreement, favorable MJO. Probably a non-event.

Yes, agree sat presentation is now finally degrading. Like the rest of this storm it has taken its time in doing so. Short range guidance did well on that. Then again, you can always find models in any situation that did well and didn't. Statistical intensity guidance in this case was crap, dynamic was solid. Probably better modeled the baroclinic factors than the statistical. Very interesting storm to watch. The signal the last several days of yet another tropical system in a couple weeks in the Caribbean is just adding insult to injury at this point. Wayyyy too far out to talk track or intensity or what have you but the models have clearly locked onto a potent tropical wave that tries to do something in the second week of November. Very long range but good model agreement on that possibility. I hope we make it to theta. I really want to be able to make horrible jokes that none of my friends understand about the theta in theta.

I think that's due to low level dry air that worked in. You won't see it necessarily on the sat. Sat shows cloud temps, e.g., tops. Not the base or depth. Looking through the vil values at KMOB, it looks like those clouds don't have much low level moisture. This happens with winter storms too...snow starts falling, air is dry, takes time to saturate the air and get that precip to reach the surface. The clouds on the backside of this storm are definitely convective--they aren't just a cold artifact, so, they still pack some likely potent and poorly resolved winds. One of the local nws sites tweeted out something about dry air entrainment a couple hours ago when prognosticating a high gust factor so I think that's what's being seen there. May also explain some of the wave patterns. To a similar degree--although the storm is over land, two things can help maintain strength in addition to the upper level divergence. First a portion of inflow has remained over the gulf the last several hours and is visible on satellite feeding into the storm's core. Second, the low levels of the atmosphere if sufficiently humid can near the coast act in a manner similar to shallow water regions and result in a longer term maintenance of strength. The third thing at play here continues to be baroclinic influence. This is a warm core system being aided by what are basically cold core dynamics. Unusual, but not unprecedented. MU

The slower phasing of the mid latitude low than forecast seems to have ended up reducing shear and instead helped to enhance upper level divergence. This baroclinic interaction seems to be responsible for why we saw such rapid strengthening today despite marginal water temps. Looking at the totality of data coming in, I think this will be post mortem upgraded to cat 3. I'm in disbelief. It has held together well as it travels inland as well. It's weakening but frankly not as fast as you'd perhaps think. It's still firing -80 degree convection in a symmetrical fashion OVER LAND. It made landfall 4 hours ago. Doesn't it know it's not over an ocean??? Talk about exceeding expectations. Who had Cat 3 landfalling end of October hurricane in NOLA on their 2020 bingo card? MU

It's a closed circulation. There will be winds on the backside, there sure were for Isaias and I have video of it. They won't show on radar. Radar relies on bouncing off water droplets and inferring vectors based on the returns. No rain, no return velocities. Does not mean there are not winds in the trunk. Weaker bc subtracting the speed of the storm instead of adding & no mix down from aloft. 40-60 is likely inland on back. MU

So, basically it has to do with the convective structure of the storm. From the eye, air twists upwards and circulates outwards in a divergent pattern. Surrounding concentric rings of convection form because certain regions concentrate momentum and energy. Imagine a bunch of big vertically oriented ovals. Air rises, is ejected outwards, and then descends further away from the center of circulation. This creates alternating regions of rising and sinking air motion. The stronger the storm, the more well organized, curved, and structured, these bands get. MU

Do you know which way that cam faces? I've been trying to figure that out. I'm at the office right now and can't tune into the weather channel to see what they're reporting. Also, aggregation of the now-occurring damage see twitter nws nola: https://twitter.com/nwsneworleans?fbclid=IwAR0y3rGWbG_B7bN8U77WgY7I0HyFqCrqvXLUqDy84gOq8cgNjfEyWncIctY

Holy ****.

NHC director is currently live on facebook giving an update.

Latest vdm reported "eyewall degrading rapidly". MU

Sigh. I could continue this conversation, but I don't feel like it's productive and helping anyone so I won't. The storm is about to make landfall and I want to see what the hhunters just found and watch what happens. We can talk about this later. I don't pretend to know more than the nhc, and I don't question their scientists who have dedicated their lives to studying hurricanes. The 5pm advisory should be out any second along with a new vdm. We can chat about 5mph differences and rounding and what should or shouldn't be done another time. MU

Not what I meant. They are usually rounded UP. Not down. Not cutoff at 2.5mph and if it's a 112 major they'd say it was 110. They'd say 115 cat 3 if winds support 112. MU

No. They said it would be upgraded if conditions indicated it should be. Wind speeds are not rounded. Anemometers are accurate, particularly those employed by the nhc, who are not using backyard anemometers from their planes and sondes to measure things. I agree this is non political. You conveniently cut off my message which was quoting a troll that quoted themselves to contradict themselves trying to start a political argument on a weather forum. *I* am not talking about politics. MU

True. I'm familiar with Colorado's situation since I had to turn back on a 14er out there in Sept due to smoke. Yes, 2020 is the year of Murphy. I live in Philly. They just announced a curfew for the city tonight so I have to leave work early to make sure I get home in time. At this point I would issue an extreme wind warning. It's on the doorstep of the city. It ain't dying now. Landfall is coming soon. MU

Ok that makes more sense. I mean, idk, I still wouldn't do that myself. If I strongly expected a tornado to go over my rental house while chasing tornadoes, I might consider a different house and *chase* the bad weather rather than find myself homeless mid season. True. You're right, there could be a problem with them. I was more stating, this storm's characteristics don't seem like they will place a true strain on the system to a degree that defects would cause problems. The main stress force on a levee is water, not wind. So, with a strong wind event but moderate surge (compared with a catastrophic event), I don't see the levee system failing even if it had an imperfection. Something could go wrong. But, I feel like that's more probable if the storm was going to be a 24+ hour event. I feel like this isn't the event that dooms the levees. It's a wind event that travels far inland. MU

I'm not sure...do people buy houses intending to be hit directly by hurricanes? 0.o ...Seems like a bad option for gaining equity! Definitely still strengthening. Holy cow. Eh, I don't think it will. They've been in the path MANY times this season. They still remember Katrina. They are very very prepared. You're never going to get 100% of the population to prepare but all in all, I believe in the population of NOLA and their EMS to have done the right prep work. This is a fast moving storm. You don't have saturated ground + strong winds, you've got strong winds. And they aren't escaping those winds. This thing is an express to New Orleans. // -Marginal case for cat 3. If they get hit with a fast moving low end cat 3, next time a slow moving, high grade cat 3 hits them...the citizenry will pay less attention. Remember the goal here is to inform the public, protect property, and save lives. That's already being done. Case exists for 110mph. Case does, technically, exist for 115mph. BUT, the environment close to shore is meh. The winds above ground will mix down to make it a major if it continues to strengthen. Also, messaging is better to say consistent cat 2 then say oh it's a cat 3 oh now back to cat 2 oh now this. If it looks extreme near shore, yeah, they'll bump it up. But needlessly upgrading could make many people want to hit the road and run away...which would be bad at this point!!! Scientifically you could make the case for Cat 3, but as I've explained before in other threads, that isn't the entire picture. If things continue along the current trend, they won't have a choice but to bump it up. -Extreme wind warning issuance would be made close to landfall. It's not on shore yet. It's got a couple hours to go. People know what is about to happen. You do NOT want to overwarn people. If you "waste" your warnings for a fast moving cat 2/3, how do you convince people to do more for a cat 5? How about a cat 1 that moves at 5mph with a giant wind field? People pay attention to the category number and extreme wind warnings are high-end warnings. The NHC won't underplay the forecast if the data support cat 3, but they won't overplay it if it's marginal. Maybe 110 at 4pm, if they feel it's solid they could bump it to 115 at 4pm or wait until 5pm. The big thing with hurricane forecasting and messaging is consistency. It's jarring to go up and down and up and down hour by hour, minute by minute. What would this forum say if they went to 115, then, at 5pm, it fell apart? What would citizens of NOLA say? I mean, I don't think it will--but the moment this thing looks a tiny bit worse, people on here will go "ah it's over!" "so much for that", "it'll be lucky to maintain tropical storm strength". In other words--moderation, folks. Frankly right now it's sitting on the border where 115 is plausible and reasonable. I'm not sure what I would do if I were the NHC, but I'm glad I don't have to be the one to make the call. -This is not as strong as Hurricane Laura was at landfall. It is not the strongest storm of the season. It's well organized though. -The levees will be fine. They are designed to handle a slow moving monster. They'll handle a fast moving mostly wind event perfectly well. Surge is a function of storm speed, storm size, wind speed and duration of time at that wind speed. And this isn't going to produce 30-40" of rain either. -I hope that people in the NOLA metro are preparing to take shelter. A 2x4 at 115 mph hurts. I assume they are, per my above comments. But, still. MU

Last post for now from me but if you have Radar Scope, the velocity imagery for the eyewall is now starting to show on radar. Being mindful of range folding (the purple you see in the image in the ring shape is range folding) and beam height, the right front quadrant shows a broad area of 115mph winds with a small pocket maxing at 131mph probably in a mesovortex. Beam height at that distance is 24k feet, lol, so that ain't mixing to the surface . But, that's still an impressive measurement and is above what I believe delta was at on its approach for the same approximate height. Indicates the system is well organized and not falling apart. MU

Aircraft data: 975 mb (down 2) 93kt wind btm 150m in SEeyewall. That would imply probably 97kt winds in NE eyewall. Peak FL winds of 102 knots, which likely supports a surface intensity of 90kts. Eye is *open* to the NW-W, and is 24miles in diameter. MU

Katrina was slower, much much MUCH bigger, and New Orleans didn't have the protection system they have now. After Katrina they made major design changes to all kinds of things. This is a strong hurricane hitting a major city, it will do damage. But it will do less damage than Katrina...and such would be true even if they were the same in every way...size speed strength, because NOLA has now redesigned their city to better withstand a Katrina. The similarity is simply that it's another hurricane poised to directly impact the city. That's not to minimize it, just, Katrinas and Harveys.. those are a really rare type of event. MU

Collectively, wow. I agree, NE eyewall pass will be impressive. Though the winds there that got sampled are still getting a boost from the fast forward speed of the storm (note the direction of storm motion compared to the wind barbs). Also want to know the surface pressure. Impressive. But, no storm jumps 25mph in 3 hours. It's landfalling in 6. Does anyone have an analog for that big of a jump that fast over eh waters? I don't! Remember that Cat 2 is still impressive here given the water temps, time of year, that none of the guidance except the extreme high end projected such an intense system. I think the consensus on the forum right now is that it's at cat 2 strength. It's going to run out of ocean before it can hit cat 3, but honestly even I am surprised how well this is holding together and strengthening so close to landfall. MU