ATL: HELENE - Post-Tropical - Discussion

[Craters]

So "center relocation" is becoming the new "annular" and "EWRC"?

Dry slot or eye forming?

Pinhole eye alert?

No.

[PDKlikatino]

Any news from recon as of yet?

[CrazyC83]

Any news from recon as of yet?

Dropsonde 986/8. Supports a 985 mb pressure.

[otowntiger]

I'd go with 60 kt and 984 mb for the intensity at the intermediate advisory based on the most recent trends (they did mention 50 kt was likely conservative and it has only gone up since).

Looks like NHC stuck with 60 mph and 991 for the 2:00 intermediate advisory. So clearly no RI / ‘bombing’ yet.

[Woofde]

I'd go with 60 kt and 984 mb for the intensity at the intermediate advisory based on the most recent trends (they did mention 50 kt was likely conservative and it has only gone up since).

Looks like NHC stuck with 60 mph and 991 for the 2:00 intermediate advisory. So clearly no RI / ‘bombing’ yet.

Rapid intensification is likely starting right now, they went with 991mb, but that was without data. Recon just reported a dropsonde of 986mb. That's a solid drop compared to last mission.

[PavelGaborik10]

Only if the center is in the middle of the convection, it’s been outside of it all day, we’ll know soon

It doesn't need to be directly in the "middle" to "bomb" as things stand, though it's clearly well on its way there if not already....we're talking about a center that was literally exposed just early this evening.

Sure it doesn’t have to be dead center, but there’s been convective blowups all day. The center was outside all of it up until the last recon, we still don’t know if it’s tucked in there or not.

Of course we do, the current explosion is massive and there is no exposed LLC

Unlike earlier, we've seen significant pressure drops, improved outflow and microwave from as many as 6 hours ago showcased a developing inner core.

This thing is intensifying at an impressive rate and has been for hours now, recon showcasing a presure of now 986 mb confirms all of this.

[ElectricStorm]

Pressure gradient doesn't look very tight to me so it makes sense why winds are still at 50kts (based on the first NE pass) despite the drop to 985mb. With a storm like this pressure will probably be quite a bit lower than you would expect for any given wind speed. Basically the opposite of Beryl which hit 145kts+ without even dropping below 930.

[ElectricStorm]

09L HELENE 240925 0600 20.3N 85.9W ATL 55 986

[Keldeo1997]

Storm hasn't moved at all since last pass. Maybe just barely SE of NHC location

[NC George]

It looks like it might hit Yucatan. Now that a CDO is expanding we will not be able to see the center. Are there any radar loops in the area?

https://www.rainviewer.com/radars/mexico.html

Just looked and it seems it blends the radars from Mexico, Cuba and the US, because there is coverage from the Yucatan all the way across Cuba and into Florida.

[kevin]

Dropsonde supports 984 - 985 mb, down 1 mbar from the previous drop.

[kevin]

55 kt measured at the surface in a max. wind band. The highest SFMR measured so far is 65 kt and the highest FL winds are 58 kt. Together this blends to 55 - 60 kt and a pressure of 985 mbar.

[ChrisH-UK]

Recon has just got 65 knots in the eye wall.

[Chris_in_Tampa]

Maybe others know this, but I didn't. But it seems the NHC's storm tide values (tide + surge, but not including waves) relate to the MHHW datum.

This blog post from the NHC:
https://noaanhc.wordpress.com/2016/01/2 ... -mmm-good/

Says...

"Why Does NHC Use MHHW When Looking at Water Level Observations?"

"NHC and NOS consider anything landward of the MHHW line (marked as the supratidal zone in the graphic) as normally dry ground."

The same is also said here:
https://slosh.nws.noaa.gov/petss/datums.php

"Mean higher-high water (MHHW) has a similar meaning to MLLW, except it is the average of all daily highest tide measurements. The National Hurricane Center (NHC) considers MHHW to be the 'above ground' datum. In other words, any water reaching above this datum has potential to cause flooding inland."

From an elevation certificate I had to have done by someone coming out to my house in 2017, I know the NAVD datum values.

My house:
8.10 feet above NAVD datum

My garage:
7.37 feet above NAVD datum

I converted that using this datum info for the station nearest me:
https://tidesandcurrents.noaa.gov/datum ... id=8726607

And now know that for the MHHW datum my values are:

My house:
7.316 feet above MHHW datum

My garage:
6.586 feet above MHHW datum

And I can relate that to the 5 to 8 feet currently forecast for Tampa Bay. (but that does not include waves, so I would flood sooner than that even though I'm on a canal)

And the elevation certificate could be wrong. But, it's a guide I can use. I wrote down all the tide information in case I lose power and need to reference it.

Edit to add this...

Here is the MHHW datum for the station closest to me:
https://tidesandcurrents.noaa.gov/water ... =6&action=

So I can check things more easily when using that datum.

The "MHHW" datum is the default:
https://tidesandcurrents.noaa.gov/inund ... ame=Helene

That link has all the various stations ahead of the storm. Once you click it there might be a forecast guidance option on the chart for a station that you can select with the note below it:

"During tropical cyclones, water level Forecast Guidance data are released for limited public utility and should be used with appropriate caution. It does not represent the official NOAA water level forecast."

It's not available past Thursday at 8pm EDT as of posting. (make sure to note whether it is set to GMT or your local time, LST/LDT) But, it should be used with caution for those looking up information.

[caneman]

Does anyone know how accurate the IBM model is this close in? I just read that this model takes Helene in around Cedar Key.

Article i found on it. I guess it's based off AI
https://research.ibm.com/blog/foundatio ... er-climate

[Keldeo1997]

Got a large Eyewall open to SE

[redingtonbeach]

Does anyone know how accurate the IBM model is this close in? I just read that this model takes Helene in around Cedar Key.

Article i found on it. I guess it's based off AI
https://research.ibm.com/blog/foundatio ... er-climate

If you mean the GRAF model, it has won a round here and there but is hit and miss. As of 4:30 AM EST, it is aligned on path with the 0Z Euro with a more easterly landfall and with the SHIPS model on intensity with a low-end Cat 4.

[Hurrilurker]

Outflow pushing out those fine radial tendrils, that's a bad sign. I think NHC is going to end up revising upwards for 24-36 hours.

[Keldeo1997]

Also, the the NNW turn may have just started. If Cuba radar is correct, then it has gained half a degree of latitude in 2 hours. Bad news if you were banking on Yucatan disrupting it

[cycloneye]

Here goes Josh to another chase.

 https://x.com/iCyclone/status/1838812448536826064