ATL: FLORENCE - Post-Tropical - Discussion

[tallywx]

5pm discussion alludes to the new disturbance in the W. Carib/GOM affecting ridge strength. How would that interplay exactly? Seems like hedging in the wording.

[EquusStorm]

Well if the OHC is that frightfully high this thing has three days to hit C5 - the official forecast is 135kt so I see no reason why it wouldn't; a storm for the record books in every way

[Hammy]

From discussion: "Unfortunately, the models were right." Cat 5 forecasted.

Not quite. Forecast is "just" 135 kt... a high Cat 4.

From my observation, they never forecast actual Cat 5 intensity for a hurricane that hasn't previously reached it.

[Vdogg]

5pm discussion alludes to the new disturbance in the W. Carib/GOM affecting ridge strength. How would that interplay exactly? Seems like hedging in the wording.

It could mean that ridging might be weaker than expected, which is why some models are shifting north and east. They have adjusted the track north somewhat, but still west of the model consensus. Tonight's Euro will weigh heavily on what they do with watches and warnings tomorrow.

[DestinHurricane]

How warm is the water around the coast? What can stop it from making landfall as a cat 5?

[Ken711]

5pm discussion alludes to the new disturbance in the W. Carib/GOM affecting ridge strength. How would that interplay exactly? Seems like hedging in the wording.

The weakness in the ridging which the models seemed to pick up on with some like the Euro moving a little east. How much further east is the question. I see they took out a small section of SC coastline in the cone and extended the cone further over the VA/MD side.

[jdjaguar]

From discussion: "Unfortunately, the models were right." Nearly Cat 5 forecasted. (Cat 5 on old saffir scale at 155mph before the 2012 changes)

What was the rationale behind changing from 155 to 157?

[jdjaguar]

How warm is the water around the coast? What can stop it from making landfall as a cat 5?

Shear and EWCR

[Hammy]

From discussion: "Unfortunately, the models were right." Nearly Cat 5 forecasted. (Cat 5 on old saffir scale at 155mph before the 2012 changes)

What was the rationale behind changing from 155 to 157?

I think it was 156 before--but the change was made so that when rounding, all three measurements (MPH, KTS, KPH) would round in the same direction.

[drewschmaltz]

How warm is the water around the coast? What can stop it from making landfall as a cat 5?

Warm

[Shell Mound]

5pm discussion alludes to the new disturbance in the W. Carib/GOM affecting ridge strength. How would that interplay exactly? Seems like hedging in the wording.

It imparts stronger mid-level ridging over the Bahamas and SW Atlantic (Sargasso Sea), owing to diabetic heating via convection. A bigger influence on the potential landfall location is the weak upper low to the WNW of Florence. That feature may impart a slight weakness that induces a slight northward component to a strengthening, stacking Florence. The interaction between the Bahamas ridge, the upper low, and Florence likely means the EPS members show landfall too far SW. That does not mean that the GFS solution is correct; it is likely too far NE. However, landfall is likely to occur closer to Morehead City-Ocracoke than to points farther SW. The gradual turn to the WNW has clearly begun sooner than expected, based on satellite imagery, and Florence is thus deviating to northward of the short-term forecast positions. Anyway, the EPS/ECMWF have a notorious tendency to overestimate ridging, while the GEFS/GFS tend to underestimate it.

[Ubuntwo]

Double wind maximum?

[Aric Dunn]

the last hour or so it has picked up the pace. heading about 280 to 285

[Aric Dunn]

Since there have not been any VDM in a while... here are the center passes.

[meriland29]

What is ger current latitude?

[Shell Mound]

Rather than Wilmington-Topsail Beach, a landfall near Morehead City-Ocracoke looks to be in line. A track toward this area would keep the most significant rain and wind to the east of Raleigh-Durham, over a much more sparsely populated area with less infrastructure, relatively speaking (except Rocky Mount-Wilson-Greenville). The fact that Florence has clearly turned earlier than expected and is N of the short-term forecast points likely takes the worst-case scenario(s) out of play, fortunately. The Caribbean disturbance and weak upper low to the WNW of Florence, along with Florence's rapid deepening, are producing a sufficient weakness to nudge the track toward the consensus models and GEFS/GFS vs. the SW-biased EPS/ECMWF. This is very good news in terms of impacts based on population density and property values.

[Extratropical94]

What is ger current latitude?

Latest pass was at 25.3-25.4

[johngaltfla]

Jesus, Flo has become quite impressive in the past 24 hours. Based on current reports and pressure drops, I wonder if we could see an 880ish-890ish millibar reading before she finishes peaking.

[dspguy]

Missing one forecast point slightly couldn't mean less to future track 5 days out. She also missed a forecast point earlier to its south.

Wait, it is NORTH of a forecast point suddenly? I thought it was staying south of the forecast all day. Is this something that occurred in the last few hours?

It's been stair-stepping/wobbling a bit today, so the overall motion is somewhat dependent on when you choose to draw a line between two points. In any case, projecting to miss a single forecast point to the north (or south) means little unless the storm is also showing sustained motion in that direction. Bottom line is that it's on track, and "track" should not be interpreted as a fixed line 1 inch across.

Thanks to you and tarheelprogrammer for the explanation. I just recall hearing a lot of "it isn't turning" this morning. Came back from work and suddenly it was north of some points. Was surprised is all. Is it possible that if it continues staying north of the track, it winds up further east/north by the time it reaches OBX?

[meriland29]

Rather than Wilmington-Topsail Beach, a landfall near Morehead City-Ocracoke looks to be in line. A track toward this area would keep the most significant rain and wind to the east of Raleigh-Durham, over a much more sparsely populated area with less infrastructure, relatively speaking (except Rocky Mount-Wilson-Greenville). The fact that Florence has clearly turned earlier than expected and is N of the short-term forecast points likely takes the worst-case scenario(s) out of play, fortunately. The Caribbean disturbance and weak upper low to the WNW of Florence, along with Florence's rapid deepening, are producing a sufficient weakness to nudge the track toward the consensus models and GEFS/GFS vs. the SW-biased EPS/ECMWF. This is very good news in terms of impacts based on population density and property values.

Hopefully, but I think it is too early in the change in latitude to think the worst case scenario is potentially off the table..especially given the fact she has strengthened sooner and stronger than previously forecast