ATL: IRMA - Models

[SouthFLTropics]

Saves Luis from a direct landfall on PR but at 100 hours that's too close for comfort.

[gatorcane]

Ridge looks stronger than 00Z but so does the trough

[Aric Dunn]

Does anyone know if the adjustment techniques used by CFAN are actually increasing the forecast skill? According to Jeff Master's most recent post, the adjusted ECMWF operational run (red line) takes Irma right into southern Florida. The same scenario is shown by three of the five so-called "high probability clusters" (which are probably adjusted EPS members). However, the WSW movement in the Bahamas seems very suspect to me...



Source: https://www.wunderground.com/cat6/hurricane-irma-track-towards-lesser-antilles

What is that red line? Why is that RED LINE going right over my house?!?!?!?!?

that WSW movement would be irma missing the trough..

[northjaxpro]

not to rhyme.. but its slower and lower...

Basically all models so far today have shifted SW overall.

Yes, a very noticeable SW shift on the EURO 12Z.

[SFLcane]

Nearing SE Bahamas at 120hrs...

[TheStormExpert]

Bahamas still in play.
https://i.imgur.com/f3HEVXZ.png

Looks like a carbon copy of the 12z HWRF.

[sma10]

Well... Irma a bit lower and trough not digging quite as far ... not a particularly good combination

[SouthFLTropics]

Ridge looks stronger than 00Z but so does the trough

That makes sense...Alonyo referenced it earlier. Stronger trough to the west pumps up the ridge to the east. For every action there is an equal and opposite reaction.

[alienstorm]

UL High seems to be stronger not good

[Aric Dunn]

120 hours.. the trough came to a dead stop.. hit a brick wall this will be interesting..

[Michele B]

If you want an out to sea scenario, you want a WEAK TROUGH!!! This is said many times, but needs to be repeated. A stronger trough is going to have a sharper tilt, if not a negative tilt. That will only bring the storm inland. A weak trough is more zonal

I hope I can shed a little light on this. Please, promets, correct me if I state this wrong:

Think of a LOW pressure trough like a bowl...it will draw the storm INTO it, like water spilling INTO a bowl.
A HIGH pressure ridge is like the bowl turned upside down. It will repel the storm AWAY from and around it.

Michelle, you are genius. You have finally explained the high pressure ridge and the low pressure trough thing in a way I can understand...

You're welcome! But don't thank me! I think it was explained this way by Brian Norcross a long time ago on local Miami TV. I love that man. He's very knowledgable yet able to explain difficult meteorological concepts in a simple way.

[Hurricane Andrew]

EURO says FL needs to pay attention...trough moving in...will there be enough interaction?

[NJWxHurricane]

Well... Irma a bit lower and trough not digging quite as far ... not a particularly good combination

trough is digging quite good

[Alyono]

the storm is actually moving faster today. The faster solutions may be the ones to look at

Neither fast nor slow is good though. Either the trough will force it into the USA or the ridge will force it into the USA

[sma10]

Does anyone know if the adjustment techniques used by CFAN are actually increasing the forecast skill? According to Jeff Master's most recent post, the adjusted ECMWF operational run (red line) takes Irma right into southern Florida. The same scenario is shown by three of the five so-called "high probability clusters" (which are probably adjusted EPS members). However, the WSW movement in the Bahamas seems very suspect to me...



Source: https://www.wunderground.com/cat6/hurricane-irma-track-towards-lesser-antilles

What is that red line? Why is that RED LINE going right over my house?!?!?!?!?

that WSW movement would be irma missing the trough..

I'm afraid that might be a possibility. We'll see how the run plays out, but Irma is definitely further SW and the trough appears to be swinging thru with slightly less depth

[Michele B]

Does anyone know if the adjustment techniques used by CFAN are actually increasing the forecast skill? According to Jeff Master's most recent post, the adjusted ECMWF operational run (red line) takes Irma right into southern Florida. The same scenario is shown by three of the five so-called "high probability clusters" (which are probably adjusted EPS members). However, the WSW movement in the Bahamas seems very suspect to me...



Source: https://www.wunderground.com/cat6/hurricane-irma-track-towards-lesser-antilles

What is that red line? Why is that RED LINE going right over my house?!?!?!?!?

that WSW movement would be irma missing the trough..

I know, Aric. It was sort of "gallows humor."

[northjaxpro]

Ridge looks stronger than 00Z but so does the trough

That makes sense...Alonyo referenced it earlier. Stronger trough to the west pumps up the ridge to the east. For every action there is an equal and opposite reaction.

Yes. I agree. I mentioned thepumping the ridge possibility earler in the week. We may be seeing that here.

[Happy Pelican]

 https://twitter.com/crankywxguy/status/904032478276530177

Love me some Cranky Weather Guy. He's absolutely one of my "go to" twitter sources. Always level headed and never one to fear monger or sensationalize.

[xtyphooncyclonex]

Been lurking for the past 2 days after hearing about Harvey. Really feels like a classic long-tracker super typhoon though this may pose a threat to land. Have several close relatives in Florida and a friend as well. 12z is a bad run.

[Steve]

If you want an out to sea scenario, you want a WEAK TROUGH!!! This is said many times, but needs to be repeated. A stronger trough is going to have a sharper tilt, if not a negative tilt. That will only bring the storm inland. A weak trough is more zonal

I hope I can shed a little light on this. Please, promets, correct me if I state this wrong:

Think of a LOW pressure trough like a bowl...it will draw the storm INTO it, like water spilling INTO a bowl.
A HIGH pressure ridge is like the bowl turned upside down. It will repel the storm AWAY from and around it.

Michelle, you are genius. You have finally explained the high pressure ridge and the low pressure trough thing in a way I can understand...

It's a decent spacial representation. You also have to factor in the flow around them. The flow around a high pressure in the northern hemisphere is clockwise. The flow around low pressure is counter-clockwise. The wind flow influences storms slightly differently depending on strength in as much as how they are represented as a "cork in the streamflow." A general rule of thumb on that is that weaker storms are more often influenced by lower level steering whereas mature storms will often be guided by atmospheric flow farther up. Some people mistake this for weak always going west and strong always going poleward. That's greater than 50% of the time going to be correct. But there are 1 or 2 examples almost every season where it doesn't work like that. But if you know at what level a system is being steered, you can usually look at that level on a model (be it at 700mb, 500mb or even higher than that in some instances) and see why it's doing what it's doing with the vort at 850mb.