ATL: LAURA - Post-Tropical - Discussion

[LarryWx]

GFDL and HWRF were the go-tos for intensity on intensity on this board back in 2005-2008, so I'm surprised HWRF's reputation has fallen behind its performance.

What I tend to see pros recommend (or what they should recommend, at any rate) is not relying on any one particular tool for forecasting, but rather pay attention to trends (both model trends with the storm itself since its formation, and climatological trends with storms of similar track so you can compensate for any systemic biases in the models e.g. the tendency for many models to underestimate ridges and overestimate troughs, thus the infamous rightward bias), the consensus aids, and how tightly the ensembles begin to consolidate or not (which reflects actual uncertainty in the forecast, unlike the essentially useless NHC "cone of uncertainty"); the HWRF is good for intensity, the EURO is good for track, but the most accurate forecasts for both track and intensity are the HCCA and TVCN/IVCN consensus tools and the FSU Superensemble (which is generally even slightly more accurate than the NHC official forecast for track and intensity, but all four are roughly comparable).

One reason why HWRF's reputation is so bad is because people don't use it correctly. So many like watching it blow up invests into major hurricanes, but that's not what the model should be used for. If you give HWRF recon data and a defined system, it can perform extremely well.

Except 24 hours ago the HWRF was N of the Big Islands than brush Keys and on to its Cat 5 status.

Bingo about the HWRF. It did poorly up through 12Z yesterday. Also, there's no question that it has a bias of being too strong. Bias doesn't mean it is always too strong but rather that it is usually too strong...too strong much more often than too weak. And sometimes 30-50 mb too strong.
I don't see any reason to praise this model.

[Jr0d]

What is happening on the NE tip of Cuba? It kind of look like a MLC is shooting of along the coast.

Despite the fairly well defined LLC south of Gitmo, I would not be surprised if the mountains spin of a few other vortices.

[NDG]

Too bad the recon is returning already.

[alienstorm]

Laura just ESE of Guantanmo Bay

[NDG]

Radar and recon confirms that Laura is taking on a NW heading during the last few hours.

[LarryWx]

So, the 12Z Euro has it landfall near 1,001 mb, which seems way out to lunch to me even when taking into account Marco's wake. OTOH, I think the HWRF's 928 mb is largely due to the HWRF being the HWRF and possibly not taking into account Marco's wake..

As of now, I'm wild guessing the average of the two at landfall: 965 mb with a likely range of 955-975 mb.

[Keldeo1997]

 https://twitter.com/pppapin/status/1297628713245454336






Reason why Laura is moving W instead of WNW. Marco is enhancing the ridge and pushing Laura southward

[SouthernBreeze]

Which is why I'd think earlier weakening of Marco could cause track shift more N and or E

[wx98]

They went with 50 kts at the update.

[Highteeld]

https://twitter.com/crankywxguy/status/1297621168070041600

This is the same person that thought Michael wasn't a category 4 right?

Yes. He just called it a "blob" the entire time. I unfollowed him after his terrible coverage of Michael

[wx98]

5:00 PM EDT Sun Aug 23
Location: 19.5°N 75.2°W
Moving: WNW at 21 mph
Min pressure: 1000 mb
Max sustained: 60 mph

[Jr0d]

What would really throw a loop would be if Laura manages to skim the N coast of Cuba

That would be bad considering Monroe County/the Florida Keys just rescinded their evacuation order for mobile homes, RVs, liveaboard vessels; and plans for business as usual( goverment offices closed, halted trash collection is cancelled).

A jog to the north would be headache. We saw how far right Marco went yesterday compared to the forecast, so I am surprised there is so much faith in the forecast right now.

I doubt it will ride the north coast and be a significant threat the Keys tomorrow....but the way this year has been going, I suppose it can't be ruled out.

[hohnywx]

CHANGES WITH THIS ADVISORY:

The government of the Cayman Islands has issued a Tropical Storm
Warning for Little Cayman and Cayman Brac.

The Tropical Storm Watch for the the Florida Keys north of Craig
Key and for Florida Bay has been discontinued.

The government of the Dominican Republic has discontinued all
Tropical Storm Warnings for the Dominican Republic.

The government of the Bahamas has discontinued the Tropical Storm
Warning for the Turks and Caicos Islands, and for the southeastern
Bahamas except for Inagua and the Ragged Islands. The Tropical
Storm Watch for the central Bahamas and Andros Island has been
discontinued.

[Kingarabian]

So, the 12Z Euro has it landfall near 1,001 mb, which seems way out to lunch to me even when taking into account Marco's wake. OTOH, I think the HWRF's 928 mb is largely due to the HWRF being the HWRF and possibly not taking into account Marco's wake..

As of now, I'm wild guessing the average of the two at landfall: 965 mb with a likely range of 955-975 mb.

Hey Larry, always good to hear from you. I agree with your landfall pressure estimates. But I think the system could be stronger since Marco is moving fast, so the time it has to upwell could be reduced. Laura will also be moving at a steady clip meaning it could spend less time over upwelled waters. We shall see. So far it's not looking good.

[Kingarabian]

Tropical Storm Laura Discussion Number 16
NWS National Hurricane Center Miami FL AL132020
500 PM EDT Sun Aug 23 2020

Satellite imagery and radar data from eastern Cuba show that the
center of Laura has been moving over water between Haiti and eastern
Cuba this afternoon. There has been a recent uptick in convection
near the center and the radar imagery has shown an increase in
banding. An Air Force reconnaissance aircraft investigating Laura
this afternoon has reported a minimum pressure that has fallen to
around 1000 mb, and winds to support an intensity of 50 kt. The
plane very recently found a small area of stronger flight-level
winds, but these winds may be associated with mesocyclone, and not
representative of the large scale circulation.

Laura continues to move briskly west-northwestward or 285/18 kt. The
track forecast reasoning remains the same as the previous advisory.
Laura should continue to move west-northwestward to the south of a
deep-layer ridge that is forecast to build westward across Florida
and the eastern Gulf of Mexico during the next day or two. The track
guidance has continued to edge southward for the portion of the
forecast near Cuba, and the NHC forecast has again been moved in
that direction. Laura should continue moving west-northwestward
over the southeastern Gulf on Tuesday, but a turn toward the
northwest is expected Tuesday night as the cyclone nears the western
portion of the ridge. A northwestward to north-northwestward motion
should then continue around the western portion of the ridge until
the cyclone reaches the northwestern Gulf coast. The latest run of
the ECMWF has shifted significantly eastward, however its ensemble
mean and many of the stronger ensemble members remain farther west
as a stronger cyclone is likely to be steered more westward by the
deep-layer ridge. The GFS, UKMET, and HWRF remain close to the
previous NHC track, so little change was made to the official
forecast was made after 48 hours.

The intensity forecast during the next 24 hours is highly dependent
on the track and the amount of interaction Laura has with Cuba. If
the storm stays along the southern coast or just offshore, the
environment of warm water and low vertical wind shear could allow
for some slight strengthening, but little overall change in
intensity is indicated during the next 24 hours. After the center
clears western Cuba, the upper-level wind pattern is predicted to
quite favorable while the storm traverses the warm waters of the
Gulf of Mexico. The GFS, UKMET, and regional hurricane models all
indicate significant deepening, and the NHC intensity forecast has
been adjusted slightly upward. Although not explicitly shown, Laura
could threaten the northwestern Gulf coast near major hurricane
strength.

Users are again reminded to not to focus on the exact details of
the track or intensity forecast at the longer range as winds, storm
surge, and rainfall hazards will extend far from the center.

Key Messages:

1. Tropical storm conditions are expected across portions of the
Haiti, the southeastern Bahamas, and Cuba through Monday. Heavy
rainfall is likely across Haiti, Cuba, and Jamaica through Monday
and these rains could cause mudslides and life-threatening flash and
urban flooding.

2. Tropical storm conditions are possible over the Middle and Lower
Florida Keys and the Dry Tortugas on Monday.

3. While the details of the long-range track and intensity forecasts
remain uncertain, Laura is forecast to strengthen over the Gulf of
Mexico and there is an increasing risk of dangerous storm surge,
wind, and rainfall impacts along portions of the U.S. Gulf Coast by
the middle of the week. This could result in a prolonged period of
hazardous weather for areas that are likely to be affected by Marco.
Interests along the Gulf Coast should monitor the progress of Laura
and Marco and updates to the forecast during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 23/2100Z 19.5N 75.2W 50 KT 60 MPH
12H 24/0600Z 20.6N 78.3W 50 KT 60 MPH...NEAR CUBA
24H 24/1800Z 21.8N 81.7W 50 KT 60 MPH...NEAR CUBA
36H 25/0600Z 23.3N 84.9W 55 KT 65 MPH...OVER WATER
48H 25/1800Z 24.7N 87.7W 60 KT 70 MPH
60H 26/0600Z 26.1N 90.2W 75 KT 85 MPH
72H 26/1800Z 28.0N 92.5W 90 KT 105 MPH
96H 27/1800Z 32.7N 93.5W 45 KT 50 MPH...INLAND
120H 28/1800Z 37.0N 88.0W 25 KT 30 MPH...POST-TROPICAL

$$
Forecaster Brown

[toad strangler]

New NHC disco says a major is a possibility

[aspen]

The 5pm track is yet another southern shift, one that avoids most of Cuba and has only two points of landfall: the start and end “hooks” of the island. The NHC keeps it at 50 kt for this time but mentions the possibility of slight strengthening. If Laura does keep to this path, it’ll emerge into the Gulf with a decent structure and be better primed for RI. However, Laura has shown she doesn’t like to follow the track we think she’s supposed to go, so I’m not ruling out a shift to the north.

[HurricaneEdouard]

So it's essentially just for entertainment intensity-wise prior to recon data. I did notice it had more realistic forecasts with Gonzalo once the plane got out there.

I wouldn't say it's just for entertainment - it has been remarkably consistent with Laura's intensity forecast compared to the other models and if a major hurricane verifies in the Gulf, it would have been realistic from the get-go regardless of recon data - but the way people incorrectly use it, as zhukm29 points out, probably is for entertainment. I used to be a regular back on the sadly now-dead FLHurricane forums and hypecasting, model wars and frenetic model-watching were always the problem compared to the actual long-term trends of the models themselves.

I was there too (I believe as Rabbit) and migrated here once it started fading. Sad as that was my introduction to the online weather community.

Are the HWRF's intensity forecasts best disregarded for storms that are yet to have recon flights?

HWRF has a bullish bias in intensity forecasts, so from anecdotal experience, these biases are amplified and more likely to fail with less data i.e. before recon flights. But that's purely anecdotal, and since the HWRF, statistically speaking, has one of the lowest intensity forecast errors of the models, you'd expect that if it failed that badly prior to retcon, this would weigh on its performance enough to be shown in the post-season model analyses and graphs (considering how many of those storms are short-lived storms far away from land).

I want to be clear (to another poster) I'm not singing the HWRF praises; it is, statistically speaking, one of the most reliable intensity models, but it still lags far behind the consensus aids (IVCN, HCCA and FSU Superensemble). That inaccuracy is because of its tendency to (sometimes significantly) overintensify storms, compared to some other, poorly-performing models that lag behind for the complete opposite reason. The HWRF being generally more accurate than most other models when it comes to intensity simply means that when you cut down the middle, you can weight slightly more in the direction of the HWRF while still blunting its intensity forecast to account for its bias - or, better yet, you can simply rely on the long-term trends of the consensus tools that weight it for you and are the most statistically accurate intensity forecasts around.

[lrak]

Visible satellite shows Laura being affected by the 2,500 ft wall to the north. Looks really cool... https://www.floodmap.net/

[alienstorm]

If you look closely at the loop you can see the LLC being pulled westward into the building convention to its east.

https://rammb-slider.cira.colostate.edu/?sat=goes-16&z=4&im=30&ts=1&st=0&et=0&speed=70&motion=loop&map=1&lat=0&opacity%5B0%5D=1&hidden%5B0%5D=0&pause=0&slider=-1&hide_controls=0&mouse_draw=0&follow_feature=0&follow_hide=0&s=rammb-slider&sec=conus&p%5B0%5D=band_06&x=7282&y=6985.5