ATL: IRMA - Post-Tropical - Discussion

[Blown Away]

Irma going to be a classic CV giant in size, winds, and cool scary name... Looks like close call for NE Caribbean and I'll go with climatology odds for no CONUS issue...

[cycloneye]

@wx_tiger
Only ~5% of TCs in #Irma's location make US landfall, but steering pattern suggests need to monitor. Image by the #illustrious Dr. Bob Hart.

 https://twitter.com/wx_tiger/status/902912175240617985

[AxaltaRacing24]

Irma going to be a classic CV giant in size, winds, and cool scary name... Looks like close call for NE Caribbean and I'll go with climatology odds for no CONUS issue...

The thing that people are forgetting is that if this drops SW into the hebert box, then all that "climatology" goes straight out the window. It is practically a crossover from a CV long tracker to a low-riding hurricane in position to possibly strike.

[smithtim]

one thing to keep in mind. The models that make this stronger in the next week or so have this losing more latitude due to stronger ridging higher up in the atmosphere at 500MB and above. So this is a case that stronger does not mean it will gain more latitude, just the opposite.

I know that sw turn is quite interesting... also very concerning to see 4-5 days predicting near cat2 forecast that far out in deep water and reading discussion nhc "that might be conservative"

Wayyy to early to know details track etc or honestley anything other than its something we all should watch very closely.. but definitely good idea to take time over labor day weekend refill for hurricane supplies, usual season prep etc

[artist]

Msbee, and others in the islands get yourselves prepared for the just in case.

[TheStormExpert]

I'd give it a 10-15% of a U.S. hit instead of that 5%.

[txwatcher91]

A more accurate analysis of climo would be to look at where this is forecast to be in a few days, due to the WSW movement, and then see how many storms in that location made landfall vs recurve. Most storms that form where this one did don't have such a strong HP building to the north. Euro is very good inside 5 days and shows a very pronounced WSW to even SW movement from the HP building.

[Hurricane Andrew]

Here is my beef with climatology. It is a useful tool, but just that; a tool. It is not absolute. Just because something is rare in cimo terms, does not mean that it will be extremely unlikely for this storm. Every storm, its steering patterns, etc, must be taken as an individual unit, with climo one of many considerations.

[txwatcher91]

Irma going to be a classic CV giant in size, winds, and cool scary name... Looks like close call for NE Caribbean and I'll go with climatology odds for no CONUS issue...

The thing that people are forgetting is that if this drops SW into the hebert box, then all that "climatology" goes straight out the window. It is practically a crossover from a CV long tracker to a low-riding hurricane in position to possibly strike.

Exactly, this system will likely affect land if it takes the WSW dip like the Euro and NHC show. Whether it reaches the US will depend on troughs and any ridge weaknesses.

[Blown Away]

I agree with your posts, but current thinking with regards to a potential CONUS threat is based on the Euro more than 10 days out... We are one Euro 12z curving OTS away from all this hype evaporating... JMHO of course and I will be tracking either way...

[Aric Dunn]

Its already well on its way to being a hurricane. some banding features becoming more pronounced.

[LarryWx]

So far, I've found a total of 6 storms that were 14.0N or further north when at 30W that went on to hit the Conus (all but Gloria hit as major hurricanes):

1. The storm of 1893, already mentioned, that was the only one N of 15N at 30W.

2. Storm #2 of 1915 was at 14.1N at 30W and hit TX:

http://weather.unisys.com/hurricane/atl ... /track.gif


3. Storm #6 of 1938, which was at 14.7N, 30W, also hit the CONUS (big one that hit NE US):

http://weather.unisys.com/hurricane/atl ... /track.gif


4. Storm 4 of 1947, which was at 14.3N, 30W, and hit FL:

http://weather.unisys.com/hurricane/atl ... /track.gif


5. Gloria of 1985, which grazed NC and then hit the NE US, was at 14.7N, 30W:

http://weather.unisys.com/hurricane/atl ... /track.gif


6. Fran of 1996 was at 14.1N, 30W, and hit NC:

http://weather.unisys.com/hurricane/atl ... /track.gif

[GCANE]

Tropical Storm Irma Discussion Number 1
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Wed Aug 30 2017



The initial motion estimate is 280/11. A ridge over the eastern
Atlantic is forecast to steer Irma westward over the next few days.
Thereafter, the ridge builds southwestward, which will likely cause
the storm to move, somewhat unusually, toward the west-southwest.
The official forecast puts more weight on the global models than the
regional hurricane models, which appear to have a northward bias on
this cycle. Thus, the NHC track prediction is on the southwestern
side of the guidance envelope, although not as far in that direction
as the ECMWF or its ensemble mean.


Forecaster Blake

I usually don't comment on NHC's Discussions; but, I sure like how Blake put it:
"likely cause the storm to move, somewhat unusually, toward the west-southwest"

[Patrick99]

A more accurate analysis of climo would be to look at where this is forecast to be in a few days, due to the WSW movement, and then see how many storms in that location made landfall vs recurve. Most storms that form where this one did don't have such a strong HP building to the north. Euro is very good inside 5 days and shows a very pronounced WSW to even SW movement from the HP building.

Exactly! My guess is that that percentage will continue to go up over the next few days. It's one thing to look at where it is now and say oh, only 5%....but let's look at where it is 3 days from now

[Patrick99]

Tropical Storm Irma Discussion Number 1
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Wed Aug 30 2017



The initial motion estimate is 280/11. A ridge over the eastern
Atlantic is forecast to steer Irma westward over the next few days.
Thereafter, the ridge builds southwestward, which will likely cause
the storm to move, somewhat unusually, toward the west-southwest.
The official forecast puts more weight on the global models than the
regional hurricane models, which appear to have a northward bias on
this cycle. Thus, the NHC track prediction is on the southwestern
side of the guidance envelope, although not as far in that direction
as the ECMWF or its ensemble mean.


Forecaster Blake

I usually don't comment on NHC's Discussions; but, I sure like how Blake put it:
"likely cause the storm to move, somewhat unusually, toward the west-southwest"

Unusual, but by no means unprecedented. The track of the famous 1947 storm looks particularly chilling.

[weathaguyry]

So far, I've found a total of 6 storms that were 14.0N or further north when at 30W that went on to hit the Conus (all but Gloria hit as major hurricanes):

1. The storm of 1893, already mentioned, that was the only one N of 15N at 30W.

2. Storm #2 of 1915 was at 14.1N at 30W and hit TX:

http://weather.unisys.com/hurricane/atl ... /track.gif


3. Storm #6 of 1938, which was at 14.7N, 30W, also hit the CONUS (big one that hit NE US):

http://weather.unisys.com/hurricane/atl ... /track.gif


4. Storm 4 of 1947, which was at 14.3N, 30W, and hit FL:

http://weather.unisys.com/hurricane/atl ... /track.gif


5. Gloria of 1985, which grazed NC and then hit the NE US, was at 14.7N, 30W:

http://weather.unisys.com/hurricane/atl ... /track.gif


6. Fran of 1996 was at 14.1N, 30W, and hit NC:

http://weather.unisys.com/hurricane/atl ... /track.gif

Not great that 2 of the above storms would cause catastrophic damage to my area

[ConvergenceZone]

If this storm was predicted to stay weak, then that definitely increases the chance of a US landfall. Would love to see this crank up to a Cat 5 and curve East of Bermuda. Otherwise, I think Bermuda and the Northern Islands really need to keep an eye on this

[Aric Dunn]

at this rate we may see an eye feature pop out on visible before the sun sets today..

[Aric Dunn]

If this storm was predicted to stay weak, then that definitely increases the chance of a US landfall. Would love to see this crank up to a Cat 5 and curve East of Bermuda. Otherwise, I think Bermuda and the Northern Islands really need to keep an eye on this

In most cases yeah, however the ridging appears as though its going to be quite strong and it might get farther south than the EUro despite being a strong hurricane.

[msbee]

I do not like that track! Thanks for keeping us informed though, Luis