ATL: FLORENCE - Post-Tropical - Discussion

[Blinhart]

This storm has already peaked and while still quite strong it should continue to weaken. Good news NC and SC for now.

There is no good news, yeah the winds might be down, but she has already got all this energy built up and will not go down until it starts hitting land.

[supercane4867]

Looks like hurricane force winds at flight level may extend a full 2 longitude away from the center.

[PandaCitrus]

The water is warm near the coast but only at the surface. It is not deep water and the Hurricane will upwell it. There isn't the heat content necessary to maintain strength. Hurricanes need warm water but also DEEP warm water. There was a graphic posted that showed this.

Look at this heat content map. The gulf stream is close to the coast in yellow and green but after passing the gulf stream you enter blue which is continental shelf water with low heat content. This is part of the reason why the NHC forecasts weakening after this short period passing the gulf stream.

[JBCycloneStan]

What exactly is weakening this storm? It's kind of puzzling given that it was forecasted to be in a conducive environment for strengthening.

[galaxy401]

This storm has already peaked and while still quite strong it should continue to weaken. Good news NC and SC for now.

Yeah you're right! No need to worry about the record breaking rainfall and very high storm surge. This storm is going to be a bust!

Yeah I'm being sarcastic here. Do NOT take this storm lightly.

[CrazyC83]

What exactly is weakening this storm? It's kind of puzzling given that it was forecasted to be in a conducive environment for strengthening.

Structural changes. It's been going through so many eyewall cycles that they are overlapping.

[galaxy401]

What exactly is weakening this storm? It's kind of puzzling given that it was forecasted to be in a conducive environment for strengthening.

It appears Florence is facing some southerly wind shear from the ULL off the coast of Florida. She is moving away from it though which might help it tonight until tomorrow morning but no guarantee.

[tolakram]

Look at the size of the NE windfield.

[MacTavish]

http://i66.tinypic.com/9ur8ki.png

Center is tilted pretty badly. Shear and dry air are kicking her butt. 18z HWRF showed steady weakening until landfall.

[PandaCitrus]

Very strange last hour on the IR Loop.

Convection is popping up like crazy on the east and wrapping around the deformed eye yet it's starting to look like half a storm. The south side is gone with lots of convection loss.

[CrazyC83]

Even at the edge of the flight pattern, winds are around 60-65 kt. This thing is HUGE!

[Blinhart]

The water is warm near the coast but only at the surface. It is not deep water and the Hurricane will upwell it. There isn't the heat content necessary to maintain strength. Hurricanes need warm water but also DEEP warm water. There was a graphic posted that showed this.

Look at this heat content map. The gulf stream is close to the coast in yellow and green but after passing the gulf stream you enter blue which is continental shelf water with low heat content. This is part of the reason why the NHC forecasts weakening after this short period passing the gulf stream.

http://www.aoml.noaa.gov/phod/dataphod1/work/HHP/NEW/2018254at.jpg

Surface water temps: http://www.baynews9.com/fl/tampa/weathe ... ratures-WX
Tropical intensity index: http://www.baynews9.com/fl/tampa/weathe ... e_Index-WX
Precipitable Water: http://www.baynews9.com/fl/tampa/weathe ... e_Water-WX
Ocean Heat Content: https://www.ospo.noaa.gov/data/ocean/oh ... G3_ddc.gif
Jetstream Forecast: http://images.intellicast.com/WxImages/ ... /conus.jpg

[Sciencerocks]

Why is she so lopsided all the sudden? I assume she sucked in a lot of dry air

Being gutted by mid level shear like Irene 2011, Floyd 1999, Isabel 2003. It is rare for this not to happen.

[meriland29]

I do have to note a very substantial (at least to my untrained eye) change. You can see here in the IR....

3hrs ago


Now


Thoughts? Am i just seeing things?

[Ken711]

What exactly is weakening this storm? It's kind of puzzling given that it was forecasted to be in a conducive environment for strengthening.

Structural changes. It's been going through so many eyewall cycles that they are overlapping.

Does this normally happen with most large hurricanes? Does the environment that it's tracking on play a role in this?

[RL3AO]

Just curious how they decided on these numbers. Any pro mets care to comment?

https://www.wunderground.com/hurricane/surge/wilmington_mom3.png

They use the same model (SLOSH) that produced that map. It's important to remember that your map shows the "MOM" or maximum of maximums. It's basically the theoretical maximum that can occur at every location for a given category hurricane. It's very unlikely anyone will actually hit the values shown on that map.

For the storm surge forecast they take the NHC forecast track and run the model up to 250 times making slight changes to the official forecast based on the historical forecast error (basically the cone). But not only do they account for the error shown by the cone (called the cross-track error), they also account for forward speed error (which is important when accounting for tides which the model does), intensity error, and size error. After running these ~250 slightly different tracks, they produce the storm surge inundation map which shows the "reasonable worst case scenario". For the forecast the use the storm surge values that have a 10% chance of happening.

[psyclone]

OHC maps never depict much heat near shore due to shallow water so they can be a bit misleading WRT a storm maintaining intensity up until landfall. the water in this case is plenty warm right to the shore for this system. If it struggles from here forward it isn't for lack of warmth. shear or dry air intrusions will be the likely culprit

[Ken711]

NHC update:

8:00 PM EDT Wed Sep 12
Location: 31.5°N 73.2°W
Moving: NW at 16 mph
Min pressure: 956 mb
Max sustained: 115 mph

[Blinhart]

Buoy 41002, https://www.ndbc.noaa.gov/station_page. ... m=E&tz=CST, 21.7 foot waves, 31.1 Knot winds going NNW.

[Hammy]

I see some here (and elsewhere) celebrating that it won't be as bad because weakening--does the wind reduction even mean anything at this point given how high and large the surge area is likely to be?