Major Hurricane Delta

[cptcatz]

The 12z Euro run has it intensifying from 976 to 955 between hours 24 and 48...

[Moderately Unstable]

1 hour ago, cptcatz said:

The 12z Euro run has it intensifying from 976 to 955 between hours 24 and 48...

Not that the euro is a bad model to use, but in the short-range, using high resolution models, particularly hurricane specific models, will yield more useful predictions. There's a plethora of fine-grained data to use right now from the statistical intensity guidance being put out to ensembles. If you aren't already using tropical tidbits or a similar resource, that is a good place to start.  Any one operational run of a global model isn't helpful in this type of situation. Weather behaves in a "chaotic" manner as time goes further along. A slight error in the initial intensity estimate, the wind field, ocean temp, ocean stratification, wind patterns elsewhere that will later affect the hurricane--all produce exponentially increasing levels of error as you propagate out in time.

Step one--look at the physics. Where is the storm going to encounter warm SSTs and low shear? Answer: now. Once you know that, you know where the storm should strengthen or maintain intensity. So, it should be strengthening now, if it's going to do so, as it has the right ingredients. Find model guidance that tracks with reality. Just because a model says something will happen, does not mean it will. Particularly with deep systems like hurricanes, a "small" error of 10-15 mb pressure, translates to some big differences in potential intensity! Using ensembles and clustered guidance for track and intensity accounts for this uncertainty and is statistically going to provide you with more accurate data. Step 1a, really, is at this point, look at the data from the hurricane hunters, along with sst maps, and current and 1-2 day progs for sfc, 700, 500 mb, 300 mb, 200 mb. 

In the shorter term, to be blunt, we have to first see if the strengthening off the coast verifies. For much of this storm's life, we've had vigorous (atypically) convection with very cold (e.g., high) cloud tops, but it has struggled to actually tap into the energy available to create a well formed eye wall translate all that heat into momentum and do so with a degree of inertial stability. The thing isn't near its MPI right now. The hurricane hunters are currently flying through the storm, and I haven't seen evidence *yet* of re-strengthening. That doesn't mean it won't happen, but, the storm is *supposed* to be in a good environment and for it to bomb back out, it needs to do so in the near future. It doesn't have a *ton* of time at the speed it is going in this optimal environment to actually gain more strength--about 36-40 hours. 

What I found sort of interesting looking at recent satellite imagery is that right after the storm left the coast, it tried to redevelop an eye--an actual eye. Then the insanely vigorous convection shot up again and sort of disrupted that flow state. I'm starting to wonder if perhaps the vigor of the updrafts is actually hurting the storm rather than helping it. That's not a normal conclusion you think of with hurricanes but I've seen this happen twice now with Delta and in both cases for Delta the intense convection weakened the storm and interfered with the structure of the eye. It appears now that the eye is again trying to reform next to rather than under the deep convection, which it has done a few times (that in particular is not atypical for hurricanes, the center regularly reforms adjacent to the most vigorous convection). The *outer banding structure is looking healthier now*, so if Delta keeps the convection *in* the eye down, it will likely bomb back out. But it has struggled with that so far. My conclusion at the moment is, wait to decide on what model guidance I want to go with until I get more data on the storms trends in the next few hours. I also want to see if the shear relaxes a bit more, as is forecast.

 

Final edit thought--looking at the sat, I'm thinking mid level easterly shear which has been a factor for a lot of the storms life, could be tilting these vigorous eye wall updrafts, same as you'd see in a severe weather setup, and that tilt is then causing the tops of the clouds to perhaps overshoot and overlay the eye. 

 

CD/MU

[Cheeznado]

Both the HWRF and HMON have it too strong by 15-20 mb by 00Z. Do not see any signs of RI right now so by later tonight that discrepancy may get larger. 

[Moderately Unstable]

21 minutes ago, Cheeznado said:

Both the HWRF and HMON have it too strong by 15-20 mb by 00Z. Do not see any signs of RI right now so by later tonight that discrepancy may get larger. 

Yes, I agree. The 18z intensity guidance just came out and it has again trended down--slightly, and mostly due to lower initial intensity. Most of the models made the storm a cat 3 in the 12z runs, now more keep it high end cat 2 with slower strengthening, or low-end cat 3. You can see from the spread that we should know in about 12 hours whether to go with the bullish or conservative guidance, which makes the difference between mid-2 and mid-3 by the end of the period in which strengthening is possible. The models are capturing the potential--the energy available--but not necessarily what we are actually seeing. All the guidance says, the storm should be strengthening now. The current sat presentation is as it has been--cycles of incredibly intense convection, presently that's expanding in area again, but no clearing of the eye. I'm particularly monitoring the southeast flank of the storm which appears to be currently getting eroded a bit. That appears to be an outflow interaction of some kind from another disturbance. What I will say, independent of category, is that the storm IS growing, as expected. So, from an impacts standpoint for surge, that is tracking towards "verify", in that it will be quite substantial. It may also increase the power outage numbers--most of the area in the track cone is damaged from earlier storms, notably Laura, but also Sally and Marco, and thus that large area of even TS winds will cause a lot of misery for a lot of folks. The HMON and HWRF are a bit high, but they, and the other 12z runs of things, show more strengthening perhaps as the storm begins to curve. My guess is they are estimating a more favorable shear vector after the turn. The most recent pass through by the aircraft does have the pressure down a few mb and winds have increased by around 8 knots. 

 

CD/MU

[Amped]

Next 6 hours is key to see what it does.  If a feeder band can form on the western Yucatan coast and then wrap around the north side of the storm there's a good chance it RIs again. If it keeps  the same line through the center look, it probably stays a Cat1/2.

[Radtechwxman]

Oof. New advisory has Delta down to 85mph. Man model guidance has been all over for this. NHC forecasting a high end cat 2 to low end cat 3 landfall now

[Windspeed]

Next 6 hours is key to see what it does.  If a feeder band can form on the western Yucatan coast and then wrap around the north side of the storm there's a good chance it RIs again. If it keeps  the same line through the center look, it probably stays a Cat1/2.

[Eduardo]

She's all hollowed out.  Reminds me a bit of Isidore in 2002.

[JasonOH]

In the last few frames the line of overshooting tops appears to be taking on a bit of a curved shape with the east end rotating north. May be getting some organization 

[Indystorm]

Lightning is also increasing on the ne, north, and nw sides of the system.

[Amped]

1 hour ago, Windspeed said:

Actually that shows plenty of precip surrounding the center. Also  there's already a convective burst wrapping around.    So it is probably about to take off, with a much larger eye.

[Prospero]

This is 2020, keep coming back, we'll see prophets of the end of the season, and those who predict 4s and 5s. Ultimately the final truth will laugh at us all.

 

[JasonOH]

Hot tower is wrapping around the north side of the circulation now.

[Windspeed]

Umm.. That didn't take long.

[Eduardo]

1 hour ago, Eduardo said:

She's all hollowed out.  Reminds me a bit of Isidore in 2002.

Yeah I fully withdraw this statement.  She's definitely looking better now that she's exited the YP.

[JasonOH]

11 minutes ago, Windspeed said:

Umm.. That didn't take long.

Perfect timing for that pass. Pretty much confirms what I was seeing on IR.

[Master of Disaster]

3 hours ago, Moderately Unstable said:

Not that the euro is a bad model to use, but in the short-range, using high resolution models, particularly hurricane specific models, will yield more useful predictions. There's a plethora of fine-grained data to use right now from the statistical intensity guidance being put out to ensembles. If you aren't already using tropical tidbits or a similar resource, that is a good place to start.  Any one operational run of a global model isn't helpful in this type of situation. Weather behaves in a "chaotic" manner as time goes further along. A slight error in the initial intensity estimate, the wind field, ocean temp, ocean stratification, wind patterns elsewhere that will later affect the hurricane--all produce exponentially increasing levels of error as you propagate out in time.

Step one--look at the physics. Where is the

For a new guy, your posts are extremely well thought out and informational. Props there. Thats how its done. 

[hawkeye_wx]

The mid/upper level flow is much improved from 24 hours ago.

[Windspeed]

The mid/upper level flow is much improved from 24 hours ago.

That's putting it mildly. Granted, GOM upper layer SSTs have come down. But unfortunately upper spreading divergence is bonkers. Delta's vortex is going to intensify rapidly. 28+SSTs are perfect for the kind of poleward outflow it will experience. Simply put, it's entering a hyped environment. Lapse rates are on steroids. Think this reattains Category 4 but as a much larger hurricane.

[hlcater]

5 minutes ago, Windspeed said:

12 minutes ago, hawkeye_wx said:

The mid/upper level flow is much improved from 24 hours ago.

That's putting it mildly. Granted, GOM upper layer SSTs have come down. But unfortunately upper spreading divergence is bonkers. Delta's vortex is going to intensify rapidly. 28+SSTs are perfect for the kind of poleward outflow it will experience. Simply put, it's entering a hyped environment. Lapse rates are on steroids. Think this reattains Category 4 but as a much larger hurricane.

The upper divergence and excellent poleward outflow channel are the biggest pluses for sure. 28c SSTs aren't really gonna help much, but they shouldn't really hurt either. That microwave pass was the first time I've been impressed by delta in the past 30 hours. Really thought it would explode yesterday and it probably would've gotten away with it too if it werent for that meddling shear.

[Windspeed]

The upper divergence and excellent poleward outflow channel are the biggest pluses for sure. 28c SSTs aren't really gonna help much, but they shouldn't really hurt either. That microwave pass was the first time I've been impressed by delta in the past 30 hours. Really thought it would explode yesterday and it probably would've gotten away with it too if it werent for that meddling shear.

The preceding shear isn't really going to matter much now. It's essentially size of core and how much time it will have before concentric banding could hypothetically take over. Based on that MW scan, it looks prime for RI.

[the ghost of leroy]

45 minutes ago, Master of Disaster said:

For a new guy, your posts are extremely well thought out and informational. Props there. Thats how its done. 

Thanks that’s my sock puppet

[Prospero]

I've never seen a year when the spaghetti plots were so focused on LA (or anywhere else) and hit on target a few days out.

[HKY_WX]

Definitely don't see any indications of shear and the SST's are more than warm enough. Agree with the above sentiments that this regains Cat 4 status tomorrow sometime.

[JasonOH]

Air Force recon is heading in right now and NOAA is right behind. Double recon this evening!

[STxVortex]

Been doing some comparisons of GOES satellite imagery between Delta and good ol' Harvey.

Both came off the Yucatan on a similar track, it's a month and a half later in the season for Delta, SSTs a bit lower now, Harvey was much weaker until well into the GOM [and almost invisible in the NW Carib, unlike Delta's RI there], and was somewhat smaller at this point in it's cycle life, not enveloping the whole GOM as Delta is beginning to.

So, Delta is already stoked, related atmospherics are filling the entire GOM att, and Delta appears set for some rebound RI for the next 24-72 hours. In short, Delta may be a demon cyclone after all.

[Moderately Unstable]

Sock puppet eh. What show do I star in? I can't wait for my reviews! Based on the last couple of days, RI may be relative. What was seen a couple of days ago was voracious and unusual. We should, based on the recent imagery coming in, expect I. The guidance says we should see more intensity, the microwave and IR imagery is improving, the above post referenced by Windspeed and JasonOH was in particular an "oh, well then", moment. I am taking the same approach as the NHC likely is about to right now, in not jumping the gun and rapidly changing their thinking. Hours back, folks were saying, it may be a 1! What a joke! etc. We can't swing 1-4-1-ts-4-5!. I still think a cat 3 peak is the most likely scenario. Big cat 3, maybe upper end cat 3, with extensive surge impact. But right now I go mid cat 3. Outflow does look a lot better, and historical context suggests good outflow is key in terms of sustaining and maintaining a clean core, which appears, again above, to be developing. To the two earlier posters who said the nice things/welcomed me--thank you :). It is nice to have a place to discuss weather without being looked at as though I have three heads. 

 

MU/CD

[JasonOH]

968.8mb extrap, 94kt flight level, 69kt SFMR on the inbound.

[STxVortex]

52 minutes ago, JasonOH said:

Perfect timing for that pass. Pretty much confirms what I was seeing on IR.

Me too, plus a few other bands I been perusing.

https://www.star.nesdis.noaa.gov/goes/floater.php?stormid=AL262020

[JasonOH]

3 minutes ago, Moderately Unstable said:

Sock puppet eh. What show do I star in? I can't wait for my reviews! Based on the last couple of days, RI may be relative. What was seen a couple of days ago was voracious and unusual. We should, based on the recent imagery coming in, expect I. The guidance says we should see more intensity, the microwave and IR imagery is improving, the above post referenced by Windspeed and JasonOH was in particular an "oh, well then", moment. I am taking the same approach as the NHC likely is about to right now, in not jumping the gun and rapidly changing their thinking. Hours back, folks were saying, it may be a 1! What a joke! etc. We can't swing 1-4-1-ts-4-5!. I still think a cat 3 peak is the most likely scenario. Big cat 3, maybe upper end cat 3, with extensive surge impact. But right now I go mid cat 3. Outflow does look a lot better, and historical context suggests good outflow is key in terms of sustaining and maintaining a clean core, which appears, again above, to be developing. To the two earlier posters who said the nice things welcomed me--thank you :). It is nice to have a place to discuss weather without being looked as though I have three heads. 

 

MU/CD

Pretty much right on with what I’m thinking. You’ve made some excellent posts with this storm. Great stuff.