ATL: NATE - Post Tropical - Discussion

[CrazyC83]

URNT12 KNHC 071823
VORTEX DATA MESSAGE AL162017
A. 07/18:10:10Z
B. 27 deg 40 min N
088 deg 58 min W
C. 700 mb 2966 m
D. 70 kt
E. 062 deg 19 nm
F. 149 deg 72 kt
G. 063 deg 18 nm
H. 983 mb
I. 9 C / 3043 m
J. 19 C / 3074 m
K. 4 C / NA
L.
M. NA
N. 12345 / 7
O. 0.02 / 3 nm
P. AF305 0816A NATE OB 26
MAX FL WIND 87 KT 122 / 42 NM 16:55:30Z
CNTR DROPSONDE SFC WIND 170 / 19 KT
;

[CrazyC83]

Recon no longer supports the current intensity. Peaked at 12Z perhaps, and down now? We'll see what trends hold.

Kinda hard to support it when they miss the center though.

The SFMR in the NE quad only supported about 75 kt at the most, but we need to caution to not adjust on short term trends.

[stormreader]

12z Euro edge a little to east, 10 miles east of Nola but still well west of the NHC's track.

And Euro had had a La landfall west of Miss River and then over New Orleans for a day and a half or so (solidly). So I just haven't been able to buy into the east of the river and central to east Miss track that's been advertised. Center is going to be very close to New Orleans, if not right over it.

[caneman]

Lutz Florida Just had a gust of 28mph.

very far from the storm.

Big deal. we don't even have a small craft advisory for our coastal waters. And our winds (which really have nothing to do with Nate) are far lower than they were earlier this week.

Take it easy slick. It's a discussion forum and last I checked he-she threw in an observation. Easier just to scroll past it than be snarky

[GCANE]

With 55 mm/hr rain rate earlier and a 10C warm core - its about time.

[Blown Away]

Looking more and more ragged on satellite... IMO Nate has peaked..

[Aric Dunn]

looks like we are about to see another large burst of convection..

[stormreader]

12z Euro edge a little to east, 10 miles east of Nola but still well west of the NHC's track.

And Euro had had a La landfall west of Miss River and then over New Orleans for a day and a half or so (solidly). So I just haven't been able to buy into the east of the river and central to east Miss track that's been advertised. Center is going to be very close to New Orleans, if not right over it.

If it occurs, there would be at least some increase in surge in New Orleans and especially the La coastal area southeast of New Orleans.

[Dave C]

Yes, Nate's southern quadrant and inner core are definitely experiencing south-southwesterly shear. The reason for the apparent weakening can be seen on satellite imagery. Nate has left the protective shield of its upper-level anticyclone and has outrun it. That is why convection near the inner core has decreased while outer bands have intensified. Note that upper-level winds from the southwest are converging over and just northwest of Nate. You can see that winds over Nate's inner core are from the south-southwest, while winds just to the west and northwest are from the southwest. Had these winds been diverging over a distance, they would have favored an expansion of Nate's outflow to the north and west, allowing an outflow channel to develop. That would be a jet exit region, hence divergence. However, what we see with Nate is a jet entrance region (convergence). The upper-level trough axis over the Midwest is to the northeast of Nate, not to its northwest, so the flow behind the trough axis is converging, not spreading apart. This pinches Nate and causes it to experience shear as it nears land. Also, upper-level convergence not only indicates shear, but also allows drier mid-level continental air to enter Nate from the north. This explains the arc clouds and outflow boundaries on Nate's northwestern quadrant. So Nate probably has peaked and will now weaken rather than strengthen up until landfall, which is common for late-season (October) storms that near the northern Gulf Coast (i.e., Lili of 2002), as opposed to storms that occur earlier in the year, in August and September, when continental troughs are weaker and the trough axis is sometimes farther west, allowing outflow expansion and moister low-level air, as with Camille and Harvey.

If you look at the shallower convection near the old swirl west of nate you can see its cloud tops being blown off quickly to the north. Where as the higher outflow with nate isn't being blown of so must be shear in the mid levels.

[Shell Mound]

Yes, Nate's southern quadrant and inner core are definitely experiencing south-southwesterly shear. The reason for the apparent weakening can be seen on satellite imagery. Nate has left the protective shield of its upper-level anticyclone and has outrun it. That is why convection near the inner core has decreased while outer bands have intensified. Note that upper-level winds from the southwest are converging over and just northwest of Nate. You can see that winds over Nate's inner core are from the south-southwest, while winds just to the west and northwest are from the southwest. Had these winds been diverging over a distance, they would have favored an expansion of Nate's outflow to the north and west, allowing an outflow channel to develop. That would be a jet exit region, hence divergence. However, what we see with Nate is a jet entrance region (convergence). The upper-level trough axis over the Midwest is to the northeast of Nate, not to its northwest, so the flow behind the trough axis is converging, not spreading apart. This pinches Nate and causes it to experience shear as it nears land. Also, upper-level convergence not only indicates shear, but also allows drier mid-level continental air to enter Nate from the north. This explains the arc clouds and outflow boundaries on Nate's northwestern quadrant. So Nate probably has peaked and will now weaken rather than strengthen up until landfall, which is common for late-season (October) storms that near the northern Gulf Coast (i.e., Lili of 2002), as opposed to storms that occur earlier in the year, in August and September, when continental troughs are weaker and the trough axis is sometimes farther west, allowing outflow expansion and moister low-level air, as with Camille and Harvey.

Aircraft data show that the shear and dry air have taken a toll, with SFMR supporting 70 to 75 knots at most. Flight-level winds of 87 knot in the strongest quadrant are probably less representative of the surface winds in a weakening system, and SFMR may lose some of its accuracy as a system enters shallower, shelf waters near the shoreline. So Nate has probably weakened to 70 to 75 knots at this point. Probably it will be a low-end Category-1 hurricane as it impacts southeastern Louisiana, which is manageable. The fast movement and relatively small size should reduce impacts from rain and storm surge, which are the deadliest factors in tropical cyclones. All in all, good news for the Gulf Coast, but any hurricane or strong tropical storm should still be taken seriously.

[Big Easy Breeze]

:uarrow: Euro is still very persistent of a track very close to Nola.

I agree with the EURO. I think unfortunately the Greater New Orleans metro area just may get Nate's entire eyewall passing over the city late tonight.

With its current fast forward movement, it probably will not make a move with a more northerly compnent, until after landfall. NOLA could see the center (whats left) pass directly overhead, or just 10-15 miles east of downtown. It is just hauling butt.

[tolakram]

I think it's more likely that the spot is dry air, not an eye. Radar presentation also degraded a bit. With these fast moving storms, though, who knows.

saved radar loop

[GCANE]

looks like we are about to see another large burst of convection..

That burst SE of the CoC is hot.
Clearing out the eye quickly.

[CrazyC83]

Right now it looks headed right to the SE tip of Louisiana, near Southwest Pass.

[wxman57]

With 55 mm/hr rain rate earlier and a 10C warm core - its about time.

https://i.imgur.com/Casph3Q.png

That area you circled isn't the center. The center is about 20 miles west of there, just about due south of the mouth of the Mississippi.

[wxman57]

Landfall in SE LA around 6pm. Or should that be levee-fall? Not much natural land in SE LA.

[Nimbus]

Power will be out for a while in a narrow swath where the Tropical storm/hurricane force winds can make there way to the surface but doesn't look too bad for most of the effected area.

[toto]

This is odd... Hurricane Nate is still Cat 1 and may increase to Cat 2 by landfall...
yet I saw Cat 3 earlier on a CNN news report graphic. Mistake or prophetic ??

[stormreader]

:uarrow: I think it's more likely that the spot is dry air, not an eye. Radar presentation also degraded a bit. With these fast moving storms, though, who knows.

saved radar loop
https://i.imgur.com/88lQwAN.gif

Radar presentation does look more ragged there. But not going to read to much into that just yet. Less clarity in definition makes it tougher to tell, but looks like continued strong west component and heading definitely for La coast.

[CaneCurious]

Wxman57, what do you see Nate doing? You always shoot straight and I respect your opinions/forecasts. I had to turn our local Nola news off until my favorites come back on the air.