Tropical Major Hurricane Florence

[snowlover91]

Here is a plot of the 00z EPS from last night with the most recent center position. As you can see the majority of the EPS members are too far SW and Florence is riding the northern edge. I've consistently seen this for at least two days now and it's not just the EPS doing it, the UK ensembles and most other guidance like the HWRF, HMON, etc. have been a bit to the SW just 12 hours out. It may seem like a small difference but for the coast of NC this could have an effect on where Florence stalls and what part of the coast is in the eyewall or near it.

 

[NCSNOW]

 

[packfan98]

Here is a plot of the 00z EPS from last night with the most recent center position. As you can see the majority of the EPS members are too far SW and Florence is riding the northern edge. I've consistently seen this for at least two days now and it's not just the EPS doing it, the UK ensembles and most other guidance like the HWRF, HMON, etc. have been a bit to the SW just 12 hours out. It may seem like a small difference but for the coast of NC this could have an effect on where Florence stalls and what part of the coast is in the eyewall or near it.

That's noteworthy. On the other hand, it doesn't necessarily mean that the trend will continue when it nears the coast. I think another thing we should be looking at is which models is handling the forward speed the best? This should give us guidance on where and when the storm will stall. I think we will be on pins and needles watching the storm and seeing if it will stop and change direction. It's like playing a very high-stakes game of chicken!

 

[snowlover91]

That's noteworthy. On the other hand, it doesn't necessarily mean that the trend will continue when it nears the coast. I think another thing we should be looking at is which models is handling the forward speed the best? This should give us guidance on where and when the storm will stall. I think we will be on pins and needles watching the storm and seeing if it will stop and change direction. It's like playing a very high-stakes game of chicken!

Yeah it may mean this will stall quicker if it's an indication of the WAR weakening sooner than forecast allowing more of a northern component.. but who knows really. Small shifts of 20-40 miles will have a huge impact for the NC coastline and even into upper SC depending on what this does after the stall.

 

[Webberweather53]

Here is a plot of the 00z EPS from last night with the most recent center position. As you can see the majority of the EPS members are too far SW and Florence is riding the northern edge. I've consistently seen this for at least two days now and it's not just the EPS doing it, the UK ensembles and most other guidance like the HWRF, HMON, etc. have been a bit to the SW just 12 hours out. It may seem like a small difference but for the coast of NC this could have an effect on where Florence stalls and what part of the coast is in the eyewall or near it.
View attachment 6252

Part of the problem with this unfortunately is the NHC has consistently pegged Florence's center well to the north of the HH aircraft fixes, last night's center fix before the 11pm advisory for example was 0.3 degrees north of where the HHs found it (28.1N vs 28.4N), that makes a big difference when interpreting short term verification.

 

[snowlover91]

Also interesting to note is the bias of each model. The majority have a west to southwest bias inside the 48 hour range but the AVNO (GFS) actually appears to be performing the best so far if I'm reading this chart correctly.. food for thought.

 

[ForsythSnow]

Yeah it may mean this will stall quicker if it's an indication of the WAR weakening sooner than forecast allowing more of a northern component.. but who knows really. Small shifts of 20-40 miles will have a huge impact for the NC coastline and even into upper SC depending on what this does after the stall.

A faster stall would mean Florence could maintain strength better and even take some more in. Also, it would probably have an opportunity to strengthen versus weaken if it does as there wouldn't be as much headwind for the storm as we have seen. I think the speed is what's keeping her at cat 4 versus being stronger. However, she is looking real good as of now and the SW portion doesn't look like a donut with a bite anymore. On the other hand, she may be a cat 3 at 11 because recon can't find cat 4 winds anymore.

 

[Brick Tamland]

It's like Flo was headed to Carolina Beach to party, and then at the last minute decided to go to Myrtle Beach instead.

 

[Webberweather53]

Also interesting to note is the bias of each model. The majority have a west to southwest bias inside the 48 hour range but the AVNO (GFS) actually appears to be performing the best so far if I'm reading this chart correctly.. food for thought.

GFS has done the best inside 48 hours for sure but in the day 3-5 period, which is pertinent after the stall, the GFS, HWRF, & HMON have the largest poleward biases.

 

[snowlover91]

Part of the problem with this unfortunately is the NHC has consistently pegged Florence's center well to the north of the HH aircraft fixes, last night's center fix before the 11pm advisory for example was 0.3 degrees north of where the HHs found it (28.1N vs 28.4N), that makes a big difference when interpreting short term verification.

I'm not sure their reasoning for doing that but I know in past years I've had discussions with pro mets on how the NHC uses a combo of satellite, recon data, etc with storms that have well defined eyes like Florence to fix the center. The reason being is that sometimes what recon pegs as the "center" may not be the true center of the storm due to various factors like tilting of the storm, ERC's ongoing, etc. and they try to account for these various factors.

 

[malak05]

No track is great but this one will be pretty rough for those in W. Carolina and E. Georgia the tornado threat in those Eastern bands as it passes could be pretty strong and still a pretty strong storm coming thru areas

 

[accu35]

Good Morning everyone, Look at the size of Flo and still expanding with size and wind feild. Where ever Flo hits, it's going to effect a hugh hugh part of the east coast even if your not in the center.

 

[Metwannabe]

Seeing the cirrus being "pulled" towards NC coast, certainly argues a clear path toward the SE NC coast in the short , also use the link to run the loop (interesting disturbance on the west side of Florence, no impact I'm sure but interesting to see)
https://www.tropicaltidbits.com/sat/satlooper.php?region=nwatl&product=wv-mid

 

[snowlover91]

GFS has done the best inside 48 hours for sure but in the day 3-5 period, which is pertinent after the stall, the GFS, HWRF, & HMON have the largest poleward biases.
View attachment 6253

Oh I definitely agree after 48 hours the GFS isn't doing well at all. However, for the coast of NC the most relevant period for them is the 48 hour period since 20-30 miles north or south will mean a big difference for the areas stuck in the eyewall.

 

[Webberweather53]

I'm not sure their reasoning for doing that but I know in past years I've had discussions with pro mets on how the NHC uses a combo of satellite, recon data, etc with storms that have well defined eyes like Florence to fix the center. The reason being is that sometimes what recon pegs as the "center" may not be the true center of the storm due to various factors like tilting of the storm, ERC's ongoing, etc. and they try to account for these various factors.

The hurricane hunters deploy dropsondes down to the surface of the ocean to get the center fix, they aren't interpreted from flight level, so vortex tilting does not play a role in determining the center fix, their in-situ data is superior and carries precedent. The parallax error in satellite data due to viewing angle and position of the satellite relative to the storm is often on the order of 20-25 miles which is about the magnitude of the center discrepancy between HH center fixes & what the NHC is saying.

 

[snowlover91]

EWRC appears underway with Florence as evidenced by a clear secondary wind maximum per recon. This has significant ramifications for NC as this would possibly expand the wind field and could allow for strengthening IF she completes this fairly quickly.

 

[Webberweather53]

I'm not sure their reasoning for doing that but I know in past years I've had discussions with pro mets on how the NHC uses a combo of satellite, recon data, etc with storms that have well defined eyes like Florence to fix the center. The reason being is that sometimes what recon pegs as the "center" may not be the true center of the storm due to various factors like tilting of the storm, ERC's ongoing, etc. and they try to account for these various factors.

Notice once again that the center fix determined from a dropsonde that reached the surface of the ocean is south of the eye on satellite, the GOES-16 satellite is geostationary near the equator, so as the storm moves further north, the viewing angle between GOES-16 and Florence becomes shallower, thus the parallax error increases with the satellite derived storm center moving further north from the "true" location of the surface center.

 

[snowlover91]

The hurricane hunters deploy dropsondes down to the surface of the ocean to get the center fix, they aren't interpreted from flight level, so vortex tilting does not play a role in determining the center fix, their in-situ data is superior and carries precedent. The parallax error in satellite data due to viewing angle and position of the satellite relative to the storm is often on the order of 20-25 miles which is about the magnitude of the center discrepancy between HH center fixes & what the NHC is saying.

Regardless of whether we agree with the methodology for fixing the center, the NHC is the best at what they do and they have their reasons for fixing the center where they do.

 

[Rain Cold]

EWRC appears underway with Florence as evidenced by a clear secondary wind maximum per recon. This has significant ramifications for NC as this would possibly expand the wind field and could allow for strengthening IF she completes this fairly quickly.

Seems like these usually take between 24-48 hours to complete fully.

 

[Webberweather53]

Regardless of whether we agree with the methodology for fixing the center, the NHC is the best at what they do and they have their reasons for fixing the center where they do.

They may have their reasons but this is a pretty obvious gaff on their part, I wouldn't take satellite derived data w/ parallax over actual surface measurements in the eye.