ATL: FLORENCE - Models

[Blown Away]

Past few GFS runs building more and more HP around Flo once near CONUS.

12z has Flo faster getting close to CONUS.

[drewschmaltz]

How does this even happen...

Alright I’ll bite, any Mets can chime in whether a low pressure system can just go through a high pressure system like butter?

And if so what is the mechanism causing this motion?

[SouthFLTropics]

ECMWF have it going into south carolina

12z Euro doesn't come out until later this afternoon. You're probably looking at the 00z.

[Hurricaneman]

Betting a loop coming.

*Headdesks.*

Maybe try smashing your face against a wall, like momma Florence.

Although in her case apparently she'll go right through the wall...

Cue the kool aid man

[pgoss11]

Plowing NW through the ridge....

I swear the GFS has a physics problem, low pressure can’t plow through a ridge

It's not going through the ridge. It's going around the ridge.

I'm no expert but the HP is NE of the hurricane which would cause a clockwise flow around that high thus Florence going around the southwestern side of the ridge. Mets correct me if I'm wrong because I'm still learning also.

[TheStormExpert]

The continued turn into the ridge on the GFS later hours is puzzling. I wouldn't put too much stock into it. Especially with the UKMet doubling down on it's westward motion. My thoughts at this time are that the Outer Banks and possibly the SC coast are going to have to deal with this one. At this time I'm thinking points further South (FL/GA) will be ok. The Ukie may change my mind on that though if it continues its current trend.

SFT

Hasn’t the UKMET always had a left bias?

[RL3AO]

The colors aren't the ridge. The ridge is shown by the black contour lines which are geopotential height, with the thick black line I added being the ridge axis.. The ridge in the image is centered east/NE of the hurricane. The black arrows show the background flow around a ridge in that position.

The colors are just how far the 500mb heights are above climatology. The darkest orange is not the center of the ridge, it is simply where the heights are unusually high. But the center of the ridge is near Bermuda.

[edu2703]

 https://twitter.com/hurrtrackerapp/status/1037379903182831617

[MacTavish]

You guys are misinterpreting the anomaly map.

[plasticup]

[img ]https://i.imgur.com/Msj347d.png[/img]

The colors aren't the ridge. The ridge is shown by the black contour lines which are geopotential height, with the thick black line I added being the ridge axis.. The ridge in the image is centered east/NE of the hurricane. The black arrows show the background flow around a ridge in that position.

The colors are just how far the 500mb heights are above climatology. The darkest orange is not the center of the ridge, it is simply where the heights are unusually high. But the center of the ridge is near Bermuda.

Great explanation. Thanks!

[Bocadude85]

I wouldn’t put much stock in any model beyond 5 days. It is interesting that the UKMET continues its westward trend, for now it is a extreme outlier.

[RL3AO]

Example

Lets say the average 500mb height for Bermuda is 5880 meters and the average 500mb height over Quebec is 5640 meters.

If Quebec is 180 meters above average and Bermuda is 30 meters above average, then the heights will be 5820m (Quebec) and 5910m (Bermuda). So the anomaly map will be really really bright orange over eastern Canada but near normal over Bermuda. However, the heights near Bermuda are still a lot higher which is what identifies where the ridge is.

A more simple example.

It can be 15 degrees warmer than average in Minneapolis in January and 15 degrees colder than average in Miami. But Miami is still a lot warmer because the average temp in January is 60 degrees apart.

[chris_fit]

12Z CMC very similar to 12GFS... it did shift a little W closer to NC vs the 00Z run.

[tolakram]

Isn't it also accurate to say that a strong hurricane will not always follow what we see at 500mb?

[RL3AO]

Isn't it also accurate to say that a strong hurricane will not always follow what we see at 500mb?

Of course it is more complex than that, but 500mb is the best level to use if you only post one of them.

[tolakram]

Isn't it also accurate to say that a strong hurricane will not always follow what we see at 500mb?

Of course it is more complex than that, but 500mb is the best level to use if you only post one of them.

Ha, well I can't handle more complex. Thanks.

[RL3AO]

For example you can use the area averaged sounding from Tropical Tidbits in an attempt to remove the storm and see what the true background flow looks like. In this case, the 500mb winds are very weak and from the ESE while the upper level winds are much stronger and from the south. It's no surprise that the mean steering wind for a strong hurricane (say 200 to 700 mb) would lead to a motion towards the NW, even though the 500mb wind suggests it should be more towards due west.

[plasticup]

Example

Lets say the average 500mb height for Bermuda is 5880 meters and the average 500mb height over Quebec is 5640 meters.

If Quebec is 180 meters above average and Bermuda is 30 meters above average, then the heights will be 5820m (Quebec) and 5910m (Bermuda). So the anomaly map will be really really bright orange over eastern Canada but near normal over Bermuda. However, the heights near Bermuda are still a lot higher which is what identifies where the ridge is.

A more simple example.

It can be 15 degrees warmer than average in Minneapolis in January and 15 degrees colder than average in Miami. But Miami is still a lot warmer because the average temp in January is 60 degrees apart.

This should be required reading.

[Bocadude85]

Isn't it also accurate to say that a strong hurricane will not always follow what we see at 500mb?

Slightly off topic but I think it was you tolakram that had posted the model verification reports in the past? And from what I recall the UKMET was the 2nd best performing global model next to the Euro...I may be wrong though...just something to ponder.

[pgoss11]

Thanks RL for the meteorology lessons. Appreciate it!