ATL: ARTHUR - Post-Tropical - Discussion

[tolakram]

Eh...it's not really ventilation of the outflow that causes the strengthening, but you've basically got the right idea. QG dynamics will tell you that divergence occurs in the upper troposphere ahead of an upper level trough because the winds in a trough are subgeostrophic (and the winds in the downstream ridge are supergeostrophic). So the winds exiting the trough are faster, and you horizontally advect more mass out of a region ahead of a trough than you advect in. Coincidentally, this is also the area where you often see strong SW winds aloft, which causes the cirrus outflow to expand over a large area. But it is really the large-scale divergence and vertical motion in the upper-troposphere that allows the strengthening. This process is baroclinic enhancement of a tropical cyclone.

Thanks for the explanation.

[Alyono]

Not a cane... if anything, the winds are weaker this time

[Hammy]

Winds seem to be somewhat lower than earlier.

[bamajammer4eva]

The band of storms that was over Ga and Fl earlier has pushed west and is now causing surprise severe storms at this hour in the Tallahassee area. Looks to have originated from Arthur.

Image from earlier

[Time_Zone]

EC is around 967 as it makes its closest approach to the Outer Banks

dont have the scaled winds yet, but it looks to be around 95-100 KT using the raw winds

I highly doubt it gets anywhere near 100 KTS

what reasoning do you have?

Just the fact that this thing hasn't been able to intensify yet and is running out of time. Judging from the latest winds found...it's actually managed to weaken a little bit.

[Aric Dunn]

Not a cane... if anything, the winds are weaker this time

agreed.. looking at that.. even at 10k ..


btw i have seen them fly at night for hurricanes many times well below 10k.. they often climb for various reasons..

[Alyono]

some say this is weakening, yet the pressure is falling...


what is happening is that the wind field is becoming more symmetric. Based upon the aircraft data, the strong winds are more evenly distributed around the eyewall. I think the same thing happened with Debby in 2008 where it was a 965mb pressure and only a midgrade cat 1. However, instead of only a small area having cat 1 winds, the entire eyewall did

[Aric Dunn]

some say this is weakening, yet the pressure is falling...


what is happening is that the wind field is becoming more symmetric. Based upon the aircraft data, the strong winds are more evenly distributed around the eyewall. I think the same thing happened with Debby in 2008 where it was a 965mb pressure and only a midgrade cat 1. However, instead of only a small area having cat 1 winds, the entire eyewall did

yeah dry air and other factors tend to lead to a struggling system that can become fairly uniform in their pressure field over time. they tend to draw in everything to maintain only the inner core region..

[Hammy]

some say this is weakening, yet the pressure is falling...


what is happening is that the wind field is becoming more symmetric. Based upon the aircraft data, the strong winds are more evenly distributed around the eyewall. I think the same thing happened with Debby in 2008 where it was a 965mb pressure and only a midgrade cat 1. However, instead of only a small area having cat 1 winds, the entire eyewall did

Is this sort of similar to the eyewall replacement cycles seen in stronger storms?

[Alyono]

recon found 988mb, but with 11 KT surface wind. 987mb is the pressure. Only slowly intensifying.

[Alyono]

some say this is weakening, yet the pressure is falling...


what is happening is that the wind field is becoming more symmetric. Based upon the aircraft data, the strong winds are more evenly distributed around the eyewall. I think the same thing happened with Debby in 2008 where it was a 965mb pressure and only a midgrade cat 1. However, instead of only a small area having cat 1 winds, the entire eyewall did

Is this sort of similar to the eyewall replacement cycles seen in stronger storms?

No, because there is not a new eyewall. I am not sure what causes the process that was observed in Dolly (not Debby like I previously said)

[meriland23]

I'm hearing two different things. Either its weakening or strengthening rapidly. Makes me scratch my head.

[hurricanedude]

aric so the 75 to 80 mph cane u thought they may find is actually weaker? Is that what I'm taking from all this?

[bahamaswx]

I'm hearing two different things. Either its weakening or strengthening rapidly. Makes me scratch my head.

Neither. It is strengthening slowly.

[Aric Dunn]

aric so the 75 to 80 mph cane u thought they may find is actually weaker? Is that what I'm taking from all this?

not , weaker.. only maintaining from before.. every time convection builds it collapses..there is still mid level dry air being pulled in.. slowly though it "should" be worked out..

[Alyono]

Earth to Kim Cunningham... the pressure is NOT 998mb. The plane had a malfunction

and how is she called a hurricane specialist? a true specialist does not make thee mistakes

[Alyono]

I'm hearing two different things. Either its weakening or strengthening rapidly. Makes me scratch my head.

Best bet is if you are in the threatened area, listen to local officials. On this forum, best bet is to listen to the mets

[Aric Dunn]

aric so the 75 to 80 mph cane u thought they may find is actually weaker? Is that what I'm taking from all this?

not , weaker.. only maintaining from before.. every time convection builds it collapses..there is still mid level dry air being pulled in.. slowly though it "should" be worked out..

I interpreted some data incorrectly..

[tolakram]

Turn off the TV!

[USTropics]

Pressure doesn't continue to fall/maintain in a weakening system. What's happening, like Alyono just alluded to, is the wind field is becoming evenly distributed around the core. Once there's a more established eyewall you'll see the winds pick up.