ATL: HELENE - Models

[ElectricStorm]

926mb but only 104kts something seems off this run I wouldn't put much stock in it

[wx98]

HWRF doing its typical “bomb out to 920s Cat 4/5” I see…

[sasha_B]

HMON shows the storm moving back offshore briefly with a second landfall in coastal SC as a 963mb tropical storm(???) around 120 hours (2pm Saturday). Others have made this remark already, but it's a bit weird that all of the hi-res hurricane models are showing such low minimum central pressures relative to wind speed for this system.

[wx98]

926mb but only 104kts something seems off this run I wouldn't put much stock in it

With a huge wind field you can get sub-930 with 105-110 kt winds. Usually it doesn’t happen on the initial intensification ramp up however. I know Katrina had a very low pressure when it landfalled as a Cat 3.

[StPeteMike]

Maybe someone can help me out. What information does HMON/HWRF take in that the GFS/Euro/Canadian don’t?

[wx98]

HWRF into Apalachicola area Thursday morning at 934 mb. This lines up closely with the 12z ECMWF and Canadian, which both landfall Thursday afternoon/evening in this area.

HAFS A and B both into the Panama area on Thursday, along with the GFS.

The ICON 18z is further east in the Big Bend Thursday night, with the HMON coming in a couple counties north of St. Petersburg/Tampa Thursday night at about 942 mb.

[ConvergenceZone]

Personally I think for either the GFS or the HMRF intensity to have a chance at verifying , this is going to have to be a depression by tomorrow night, considering landfall is only 80 to 90 hours away.

[aspen]

926mb but only 104kts something seems off this run I wouldn't put much stock in it

The HWRF always low-balls the winds whenever it has a RI-EWRC like that. A structure like that would probably inhibit that level of RI, though.

Wildly different structures on the HWRF and HAFS-A/B. The HWRF has that tiny core with an infinite EWRC, HAFS-A has a normal-sized core that starts getting sheared on Thursday morning, and HAFS-B barely even forms an eyewall.

[wx98]

Don’t know if anyone viewed the 12km NAM, but it runs over the western tip of Cuba and deepens to 970 by 6z Thursday. Same latitude as the Keys.

[Stormlover70]

Maybe someone can help me out. What information does HMON/HWRF take in that the GFS/Euro/Canadian don’t?

My understanding is they are more for strength but I could be wrong.

[Hammy]

Please tell me the HMON model isn’t reliable. I see a 940 mb storm with the eye wall slamming Pinellas County.

I mean it outperformed all the other ones last year in 3 to 5 day forecasts. But I wouldn't take it as gospel, especially the very first run

The silver lining is that, while HMON (and other hurricane models) are great at intensity forecasts, they're usually subpar for track forecasts IIRC.

Both models have a tendency of overdoing intensity similar to the NAM because they're mesoscale-level models.

[Kohlecane]

Moves so fast that it remains in the high 960s/low 970s over Atlanta. Lots of well Inland impacts on this run with an eyewall scar all the way may up to the N Georgia Mountains.

https://i.imgur.com/TMXfGcj.png

Would be suprised to see some 5-7ft surge along the Carolina beaches

[ronjon]

Let's keep an eye on model trends over the next few cycles. Becoming concerned here in Hernando County north of Tampa for eastward shifts. So far today, significant shift east in ICON from 12z to 18z. Slight shift east in GFS from 12z to 18z. Of the hurricane models, their initial runs are just east of Apalachicola for HWRF, HMON into Crystal River, HAFA west of Panama City, and HAFB near Panama City.

[wx98]

Let's keep an eye on model trends over the next few cycles. Becoming concerned here in Hernando County north of Tampa for eastward shifts. So far today, significant shift east in ICON from 12z to 18z. Slight shift east in GFS from 12z to 18z. Of the hurricane models, their initial runs are just east of Apalachicola for HWRF, HMON into Crystal River, HAFA west of Panama City, and HAFB near Panama City.

Wouldn’t be surprised to see eastward shifts either. Big Bend area isn’t out of the woods at all.

[DunedinDave]

Let's keep an eye on model trends over the next few cycles. Becoming concerned here in Hernando County north of Tampa for eastward shifts. So far today, significant shift east in ICON from 12z to 18z. Slight shift east in GFS from 12z to 18z. Of the hurricane models, their initial runs are just east of Apalachicola for HWRF, HMON into Crystal River, HAFA west of Panama City, and HAFB near Panama City.

To me the key is going to be where this storm enters the Gulf. Does it ride through the channel, does it cross over the western tip or does it go more like Charley and Ian did and over the Isle of Youth.

If it’s through the channel—I think this is more Appalachicola or maybe even further west bound.

If it’s over the west tip—More big bend bound

If it’s over the Isle of Youth—Tampa Bay or maybe even further south.

[chris_fit]

18z Euro decent amount stronger than 12z. Maybe a hair East at 90hrs.

[cycloneye]

The spaghetti models at 00z.

[StPeteMike]

The Spaghetti models at 00z.

https://i.imgur.com/dCLRIvr.png

Seems to be a degree or two off to the west. Nothing from satellite image depicts a center in that location anymore.

[AutoPenalti]

That early 0z model looks off… The center looks to be forming east of that

[USTropics]

Maybe someone can help me out. What information does HMON/HWRF take in that the GFS/Euro/Canadian don’t?

It doesn't take in additional data, it just is able to apply equations to the initial values/data and model certain atmospheric evolutions that the dynamic models (GFS/ECMWF, etc) cannot. In fact, the HWRF is interpolated based on the GFS model fields and applies the GFS as lateral boundary conditions.

The difference is, the global models don't have a resolution that allows them to actually model convection and microscale vorticity properly. Essentially vertical motion, on a magnitude scale, is rather small compared to zonal/meridional flow and and instead the global models parameterize these fields (i.e., approximates them). The hurricane/mesoscale models can actually apply dynamics to these fields to better model them by creating higher resolution 'nests'. Basically, imagine creating a box around the tropical cyclone on the GFS, the resolution may only allow for a grid of lets say 100x100. The HWRF can draw the same perimeter, but can apply a grid of 1000x1000 (made up values, but you get the idea).