ATL: LAURA - Post-Tropical - Discussion

[ConvergenceZone]

Is it just me or does this hurricane appear to be getting larger in size?

[eastcoastFL]

Laura is outpacing HWRF intensity by quite a bit. At 03z HWRF has Laura at 986 and she's already sub 980. Has a landfall at 945mb
https://ibb.co/6vhQYfM

HWRF likes to overreact on weak tropical storms by intensifying them into 930-940mb CAT4s but that's about it. In fact it underestimates strong systems just as much as it exaggerates weak ones. None of the HWRF runs have predicted the peak intensities of Michael, Dorian, and Irma before they bombed out to CAT5s.

I’m pretty sure HWRF was one of it not the only model that had Michael and Dorian bombing out to CAT 4’s and that was well before they had bombed out already. It was also the best model with Irma track wise. I’m not sure about intensity but I think it was pretty close. With this one it’s been head and shoulders above any other storm. I know it over does a lot of storms but it does get a few right.

[Kingarabian]

Also down 5.2 mb in the last 2 hour 38 min. Deepening at a rate of around 1.97mb/hr over the last few passes.

I doubt that rate is sustainable but even at 1mb an hour we’re looking at a 955mb storm tomorrow night. I hope it’s not sustainable. Could it be?

955mb is my expectation at the least for Laura within 24 hours.

[HurricaneEdouard]

Also down 5.2 mb in the last 2 hour 38 min. Deepening at a rate of around 1.97mb/hr over the last few passes.

I doubt that rate is sustainable but even at 1mb an hour we’re looking at a 955mb storm tomorrow night. I hope it’s not sustainable. Could it be?

It could be; explosive deepening is rare, but is defined as deepening of 2.5 mb+ per hour for over 12 hours or 5 mb+ per hour for over 6 hours, and rapid deepening (which, quite frankly, isn't rare for a hurricane over the Gulf) is defined as deepening of 1.75 mb+ per hour or a 48 mb drop over 24 hours.

If it continues a deepening rate of 1.97 mb per hour for 24 hours, it would just barely meet the criteria for rapid deepening (but not explosive deepening), and have a central pressure of 930 mb. Eminently plausible, in my view, although I suspect due to the size and structure of the core, the winds will lag behind the pressure for a little while (which is what we're seeing in recon).

[Blow_Hard]

Laura is outpacing HWRF intensity by quite a bit. At 03z HWRF has Laura at 986 and she's already sub 980. Has a landfall at 945mb
https://ibb.co/6vhQYfM

HWRF likes to overreact on weak tropical storms by intensifying them into 930-940mb CAT4s but that's about it. In fact it underestimates strong systems just as much as it exaggerates weak ones. None of the HWRF runs have predicted the peak intensities of Michael, Dorian, and Irma before they bombed out to CAT5s.

I’m pretty sure HWRF was one of it not the only model that had Michael and Dorian bombing out to CAT 4’s and that was well before they had bombed out already. It was also the best model with Irma track wise. I’m not sure about intensity but I think it was pretty close. With this one it’s been head and shoulders above any other storm. I know it over does a lot of storms but it does get a few right.

30s

You'd be right. I believe for Michael the Euro and GFS both had runs in the 940s and everyone was surprised but HWRF was showing low 930s and it may have even had a run or two of sub 930...

[Hammy]

Laura is outpacing HWRF intensity by quite a bit. At 03z HWRF has Laura at 986 and she's already sub 980. Has a landfall at 945mb
https://ibb.co/6vhQYfM

HWRF likes to overreact on weak tropical storms by intensifying them into 930-940mb CAT4s but that's about it. In fact it underestimates strong systems just as much as it exaggerates weak ones. None of the HWRF runs have predicted the peak intensities of Michael, Dorian, and Irma before they bombed out to CAT5s.

I’m pretty sure HWRF was one of it not the only model that had Michael and Dorian bombing out to CAT 4’s and that was well before they had bombed out already. It was also the best model with Irma track wise. I’m not sure about intensity but I think it was pretty close. With this one it’s been head and shoulders above any other storm. I know it over does a lot of storms but it does get a few right.

NAM was the first with Dorian and Michael (and on the former actually called the landfall pressure correctly.)

HWRF does tend to bring a lot of storms up to major so there's no way of knowing when it's right and crying wolf so to speak. At least with the NAM (which overdoes the pressure too often) that's often a predictor of rapid intensification even if the pressure itself is quite a bit off.

But at least neither are calling for sub-800mb pressure

[ColdMiser123]

Pressure down to 978 mb based off of the dropsonde splashing at 980 mb with 21 KT surface wind.

[CaribJam]

Laura seems to be on the way to cause a horrific disaster somewhere along the Gulf Coast. The specific areas may change over the next 24 hours, so if you are in the possible path, PLEASE TAKE THE NECESSARY PRECAUTION NOW before it's too late.

My prayer goes out for you. Stay safe.

[Keldeo1997]

 https://twitter.com/Wxmanms1/status/1298439228578312193




Even the HWRF the "Bullish" model is underestimating Laura right now

[eastcoastFL]

Also down 5.2 mb in the last 2 hour 38 min. Deepening at a rate of around 1.97mb/hr over the last few passes.

I doubt that rate is sustainable but even at 1mb an hour we’re looking at a 955mb storm tomorrow night. I hope it’s not sustainable. Could it be?

955mb is my expectation at the least for Laura within 24 hours.

That’s totally reasonable. I kind of expect that as well though I wouldn’t be shocked if it was stronger.

[Hypercane_Kyle]

Seems to be following the 12z ECMWF closely thus far in terms of intensity.

[cfisher]

WOW those dual outflow bands, I'm not sure I've ever seen it that symmetric. Also 2mb/hour might be a conservative estimate if you factor in RI once this thing has an inner core.

[Kingarabian]

Looks like it's just about done mixing out the dry air:


Also nearly the entire CDO consists of about -75/-80C cloud tops. The wind speeds in the eyewall have a great potential to be exceedingly strong even if the eye is not visible.

[Do_For_Love]

Interesting comments regarding deepening rates. I'm about to get off the computer for the night with Laura at 978 mb and deepening at roughly 2 mb/hr. I'll probably check back in around 730 am tomorrow, so 2x9=18, if she keeps steady, she'll be at 960 when I log back in. That seems reasonable to me, but we'll see what happens.

[ColdMiser123]

https://twitter.com/Wxmanms1/status/1298439228578312193

Even the HWRF the "Bullish" model is underestimating Laura right now

3z is 11 pm EDT, so we actually still have a bit for the pressure discrepancy to grow even more between the HWRF and what's observed. That may also partly explain the location differences as well.

[aspen]

WOW those dual outflow bands, I'm not sure I've ever seen it that symmetric. Also 2mb/hour might be a conservative estimate if you factor in RI once this thing has an inner core.

2 mbar/hr is already extremely rapid. Amphan bombed out at 3 mbar/hr, which I don’t see happening just yet.

[cfisher]

The 990 -> 978 drop without an inner core in 6 hours was frankly insane

[AubreyStorm]

Pressure down to 978 mb based off of the dropsonde splashing at 980 mb with 21 KT surface wind.

Isn't that a cat 2 pressure? Significant drop from earlier today when we were at 991.

[eastcoastFL]

HWRF likes to overreact on weak tropical storms by intensifying them into 930-940mb CAT4s but that's about it. In fact it underestimates strong systems just as much as it exaggerates weak ones. None of the HWRF runs have predicted the peak intensities of Michael, Dorian, and Irma before they bombed out to CAT5s.

I’m pretty sure HWRF was one of it not the only model that had Michael and Dorian bombing out to CAT 4’s and that was well before they had bombed out already. It was also the best model with Irma track wise. I’m not sure about intensity but I think it was pretty close. With this one it’s been head and shoulders above any other storm. I know it over does a lot of storms but it does get a few right.

NAM was the first with Dorian and Michael (and on the former actually called the landfall pressure correctly.)

HWRF does tend to bring a lot of storms up to major so there's no way of knowing when it's right and crying wolf so to speak. At least with the NAM (which overdoes the pressure too often) that's often a predictor of rapid intensification even if the pressure itself is quite a bit off.

But at least neither are calling for sub-800mb pressure

Good points. I looked at Nam for laughs this morning and it was 886mb lol like 175kts

[storm_in_a_teacup]

https://cdn.discordapp.com/attachments/716215692617187328/747998389920071750/93FC22F5E72948A8DD7C4D8CE78DF64C.png

Dual Outflow channels coming in hot

Or as the Encyclopedia of Hurricanes, Typhoons, and Cyclones by David Longshore put very colorfully, a sign that the storm is "digesting such large quantities of tropical air that it has had to develop a complex excretory system to deal with the overflow."

...I kind of had to stick that quote into a thread somewhere.