ATL: HELENE - Post-Tropical - Discussion

[eastcoastFL]

Over the on the models thread- after a muted 18Z following a nuclear 12Z series of runs, the high res hurricane models are swinging back to significant hurricane mode.

Upper low near the Yucatan that has been shearing PTC9 is backing W, shear should be dropping as modeled.

https://i.giphy.com/media/v1.Y2lkPTc5MGI3NjExNGM1MnVwcXYzMG9zeDF5c2NiZ3ZseHNxZWozY2RiazNoZHhzN2thNCZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/UPNCSoz2xGkhDaLBmv/giphy.gif

I think it's only the over excited H Models(can never remember the letters) that are showing anything real significant. All the others are the same or weaker, but please correct me if I'm wrong.

All of the hurricane models are H models.

[kevin]

Due to their rectangular path it seems recon missed the exact center with its current pass, but the lowest pressure measured so far is 1000.0 mbar with 9 kt winds -> 999 mbar.

[3090]

Regardless the center location does often effect models runs and intensity forecasts. I've seen it happen many times in the past . Also, there have been storms that have went from TS to Major in 24 hours Even if the forecasted strength doesn't change, remember that models aren't great when it comes to forecasting strength. We've seen it most recently with Francine when they almost all showed weakening at landfall and it never happened. So don't read much into what the models are showing in regards to strength, they make lovely liars sometimes.

Ida crossed Cuba and it didn't stop it from becoming a strong cat 4...

Correct the Western tip of Cuba is flat and won't normally impede strength.

AND spent a ton of time over the central OPEN GOM. A lot more potential for PTC9 to soend less time over the open GOM.

[kevin]

Their dropsonde work seems perfect though and the data is a bit shocking to me. 992 mbar at the surface with 15 kt winds. Supports a current intensity of 990 mbar, 10 mbar below what even the hurricane models have right now (the latest hurricane models reach this pressure about 12 - 18 hours from now).

[johngaltfla]

Over the on the models thread- after a muted 18Z following a nuclear 12Z series of runs, the high res hurricane models are swinging back to significant hurricane mode.

Upper low near the Yucatan that has been shearing PTC9 is backing W, shear should be dropping as modeled.

https://i.giphy.com/media/v1.Y2lkPTc5MGI3NjExNGM1MnVwcXYzMG9zeDF5c2NiZ3ZseHNxZWozY2RiazNoZHhzN2thNCZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/UPNCSoz2xGkhDaLBmv/giphy.gif

It looks like it's going to be tough for the system to split the channel. It might clip the western edge of Cuba.

That's bad for the Greater Tampa area. If it were closer to the tip of the Yucatan odds are it would proceed more towards the Big Bend area.

[xironman]

Half a storm. It won't hit Cuba. The center is too far west, right at the edge of the convection. Probably closer to the Yucatan.

[kevin]

Looks like recon is using this mission to do a more thorough rectangular shaped analysis of the region to get as much data as possible to feed into the models. The next recon flight will probably do more traditional center passes. They are due south now and as such will miss the region with significant convection and most likely the highest winds. Based on the dropsonde data and the wind data that we do have, I'd put the current intensity at a possibly conservative (in terms of wind speed) 991 mbar / 40 kt.

[xironman]

Their dropsonde work seems perfect though and the data is a bit shocking to me. 992 mbar at the surface with 15 kt winds. Supports a current intensity of 990 mbar, 10 mbar below what even the hurricane models have right now (the latest hurricane models reach this pressure about 12 - 18 hours from now).

https://i.imgur.com/kce1cHT.png

NHC says 1001, maybe they think an equipment failure?

[kevin]

Their dropsonde work seems perfect though and the data is a bit shocking to me. 992 mbar at the surface with 15 kt winds. Supports a current intensity of 990 mbar, 10 mbar below what even the hurricane models have right now (the latest hurricane models reach this pressure about 12 - 18 hours from now).

https://i.imgur.com/kce1cHT.png

NHC says 1001, maybe they think an equipment failure?

Hmm weird, maybe. I don't see any mention of the center dropsonde in their discussion. Maybe they're a bit unsure because of the low pressure and are waiting for more data with the next recon flight, which will most likely perform regular center passes. 30 kt is very low atm though. There are multiple 40 kt SFMR measurements. And yes, they mention that most dropsondes are around 30 kt, but that's because they didn't drop any dropsondes near the locations where you'd expect the highest winds. Not sure what their reasoning is not to call this Helene already, but they're the experts so I guess we'll just wait and see.

Edit: looks like another dropsonde (#14) was dropped at the same location and measured 1001 mbar with 15 kt so maybe dropsonde #13 was indeed faulty.

[cycloneye]

Their dropsonde work seems perfect though and the data is a bit shocking to me. 992 mbar at the surface with 15 kt winds. Supports a current intensity of 990 mbar, 10 mbar below what even the hurricane models have right now (the latest hurricane models reach this pressure about 12 - 18 hours from now).

https://i.imgur.com/kce1cHT.png

NHC says 1001, maybe they think an equipment failure?

Hmm weird, maybe. I don't see any mention of the center dropsonde in their discussion. Maybe they're a bit unsure because of the low pressure and are waiting for more data with the next recon flight, which will most likely perform regular center passes. 30 kt is very low atm though. There are multiple 40 kt SFMR measurements. And yes, they mention that most dropsondes are around 30 kt, but that's because they didn't drop any dropsondes near the locations where you'd expect the highest winds. Not sure what their reasoning is not to call this Helene already, but they're the experts so I guess we'll just wait and see.

Edit: looks like another dropsonde (#14) was dropped at the same location and measured 1001 mbar with 15 kt so maybe dropsonde #13 was indeed faulty.

What you said of waiting for the missions that will do passes. NOAA and AF planes are on route.

[eastcoastFL]

Ida crossed Cuba and it didn't stop it from becoming a strong cat 4...

Correct the Western tip of Cuba is flat and won't normally impede strength.

AND spent a ton of time over the central OPEN GOM. A lot more potential for PTC9 to soend less time over the open GOM.

While that’s true 9 will spend Most of its time in the gulf traversing some of the warmest pools of water in the gulf that have been major catalysts for previous storms. If 9 can get stacked and healthy before dipping into those warm pools it’s off to the races.

[xironman]

Looks like a dry air problem now, probably got dragged in from the ULL. That should abate as the ULL digs and weakens

[eastcoastFL]

Looks like a dry air problem now, probably got dragged in from the ULL. That should abate as the ULL digs and weakens

https://i.imgur.com/CllQPwk.gif

That and a little shear:

Southwesterly shear continues over the disturbance, though the
models are insistent that this shear will abate as an upper-level
low over the northeastern Yucatan Peninsula weakens today and
tomorrow. Otherwise, conditions look quite favorable for
strengthening over the eastern Gulf of Mexico on Wednesday and
Thursday, with the system likely moving over extremely deep and
warm waters, along with a favorable trough interaction, and many of
the forecast aids are showing rapid intensification over the
eastern Gulf of Mexico. The intensity guidance is very close to
the previous NHC intensity forecast and continues to indicate that
this system will become quite large and powerful before landfall.

[xironman]

Looks like a dry air problem now, probably got dragged in from the ULL. That should abate as the ULL digs and weakens

https://i.imgur.com/CllQPwk.gif

That and a little shear:

Southwesterly shear continues over the disturbance, though the
models are insistent that this shear will abate as an upper-level
low over the northeastern Yucatan Peninsula weakens today and
tomorrow. Otherwise, conditions look quite favorable for
strengthening over the eastern Gulf of Mexico on Wednesday and
Thursday, with the system likely moving over extremely deep and
warm waters, along with a favorable trough interaction, and many of
the forecast aids are showing rapid intensification over the
eastern Gulf of Mexico. The intensity guidance is very close to
the previous NHC intensity forecast and continues to indicate that
this system will become quite large and powerful before landfall.

Yup, and it will also transport the moisture from John's remnants to the Gulf.

[Chris_in_Tampa]

Even with a Big Bend landfall, NHC has 9 feet projected in the Tampa Bay region.

On this product that 9 feet in places means:

"*Displayed flooding values indicate the water height that has about a 1-in-10 (10%) chance of being exceeded."

That's not an NHC forecast.

"This map is based on PSURGE 2.0 guidance. Probabilistic and exceedance output can be viewed here: http://slosh.nws.noaa.gov/psurge2.0/.

The NHC isn't yet forecasting surge for places other than southwest Florida in the public advisory:

https://www.nhc.noaa.gov/text/refresh/MIATCPAT4+shtml/#:~:text=STORM%20SURGE:

It's too early yet for areas further northward.

Now there are surge forecasts from the NHC for Tampa Bay. Section on surge from the 5am EDT Monday public advisory:

STORM SURGE: The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline. The water could
reach the following heights above ground somewhere in the indicated
areas if the peak surge occurs at the time of high tide...

Ochlockonee River, FL to Chassahowitzka, FL...10-15 ft
Chassahowitzka, FL to Anclote River, FL...6-10 ft
Indian Pass, FL to Ochlockonee River, FL...5-10 ft
Anclote River, FL to Middle of Longboat Key, FL...5-8 ft
Tampa Bay...5-8 ft
Middle of Longboat Key, FL to Englewood, FL...4-7 ft
Englewood, FL to Bonita Beach, FL...3-5 ft
Charlotte Harbor...3-5 ft

For a complete depiction of areas at risk of storm surge inundation,
please see the National Weather Service Peak Storm Surge Graphic,
available at hurricanes.gov/graphics_at4.shtml?peakSurge.

Storm surge could raise water levels by as much as 2 to 4 feet above
normal tide levels in areas of onshore winds along the southern
coast of Pinar del Rio, Cuba, including the Isle of Youth.

Storm surge could raise water levels by as much as 2 to 4 feet above
ground level in areas of onshore winds within the warning area along
the east coast of the Yucatan Peninsula.

[kevin]

NOAA3 should arrive within ~1 hour followed by AF300 1 - 2 hours later so those will hopefully give us some good center passes to assess PTC9s intensity.

[Nederlander]

Over the on the models thread- after a muted 18Z following a nuclear 12Z series of runs, the high res hurricane models are swinging back to significant hurricane mode.

Upper low near the Yucatan that has been shearing PTC9 is backing W, shear should be dropping as modeled.

https://i.giphy.com/media/v1.Y2lkPTc5MGI3NjExNGM1MnVwcXYzMG9zeDF5c2NiZ3ZseHNxZWozY2RiazNoZHhzN2thNCZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/UPNCSoz2xGkhDaLBmv/giphy.gif

It looks like it's going to be tough for the system to split the channel. It might clip the western edge of Cuba.

It’s more likely to hit Cancun or split the channel than Cuba imo

[xironman]

Once it fills in, this is going to be one large TC, from Jamaica to Cozumel. It is going to be pushing a ton of water in front of it.

[Nimbus]

Hurricane Watch for Pinellas County.

Most of the low areas in Pinellas can handle 3 to 5 feet of surge.
5 to 8 ft would be a problem, paint and carpet every 500 years isn't excessive but
Oldsmar is at the north end of Tampa bay and 10 or 20 ft there would be dangerous.

Dry shear continues this morning so NINE/Helene will be steered as a shallow system and probably miss the tip of Cuba. Only 06Z run so far is the ICON with Tampa flood and Cedar Key landfall.

[aspen]

If I’m looking at and interpreting the WV loop correctly, the source of the shear is an ULL over the Yucatan backing off towards the west, not the outflow from John. Someone correct me if I’m wrong.