Disturbed weather in Eastern Atlantic (Is invest 95L)

[KWT]

MiamiHurricanes10, Wxman57 is totally correct, a -ve NAO means low pressures in the subtorpics, whilst a +ve NAO usually means a stronger subtropical high pressure and low pressure further north...

Really though thats far too oversimplifying it, you can have different types of -/+NAO!

Ivanhater, I have few doubts that'd be a major hurricane there...I seriously think we are looking at our first major...and if thats the case...I think with no real ridging anywhere in sight past 45W...I just can't see anything past a possible Bermuda threat.

[Dean4Storms]

All the NAO forecasts I've seen have it headed toward a positive phase by the end of the month. This would favor more dominant ridging over the Atlantic basin and lead to more westward traveling CV Storms!

[cycloneye]

KWT, what may be for sure is that the ACE units this system may get will be very high if the models intensity forecasts are right. That would help lift the 2010 season totals that as of today is a little shy of ten units.

Code: Select all

Season total
Storm Type ACE (104 kt2)
01L (Alex) Operational 6.7825
03L (Bonnie) Operational 0.3675
04L (Colin) Operational 1.9450
Total  9.095


[KWT]

All the NAO forecasts I've seen have it headed toward a positive phase by the end of the month. This would favor more dominant ridging over the Atlantic basin and lead to more westward traveling CV Storms!

Interesting you say that, the ECM looks like its building a strong Greenland high towards the end of that run, thats going to relaly shunt the jet well south if that were to occur and troughing would dig deeper as a result, still thats far enough out to not take too seriously!

Cycloneye, if the 18z GFS is right you'd be looking at 30-40 units from this system IMO...

[Aric Dunn]

My latest analysis of surface obs and satellite of the area is showing something a little more substantial taking shape SE of the Cape Verde Islands.. It looks like the greatest vorticity and dynamics are in place in that area. It still has a couple days before we should see an development but keep an eye on the eastern extend of the whole area as it moves west pretty slowly.

[MiamiHurricanes10]

MiamiHurricanes10, Wxman57 is totally correct, a -ve NAO means low pressures in the subtorpics, whilst a +ve NAO usually means a stronger subtropical high pressure and low pressure further north...

Really though thats far too oversimplifying it, you can have different types of -/+NAO!

Ivanhater, I have few doubts that'd be a major hurricane there...I seriously think we are looking at our first major...and if thats the case...I think with no real ridging anywhere in sight past 45W...I just can't see anything past a possible Bermuda threat.

I suggest you read this...start on page 6.

http://mailer.fsu.edu/~jelsner/PDF/Research/LongLead.pdf

[Vortex]

IMO, I think the northern leewards had better watch this extremely closely...

[TYNI]

To summarize, what I think I am reading here is that development is ALMOST a sure bet. What is not sure is how far west will this get before a recurve north occurs, if it occurs. The lack of multiple troughs in the 12Z GFS is what I am skeptical about. I don't understand how that east coast low lifting out affects the troughing (I don't expect an answer to that BTW, just need to read more...).

A long tracking monster fish is a good thing.

[MiamiHurricanes10]

"+ve NAO usually means a stronger subtropical high pressure and low pressure further north."

Yup. That's right, that's because you get ridging on the western and eastern portion of the North Atlantic. When this happens it displaces the middle tropospheric trough of lower pressures to the north. The trough, which induces hurricane movement to the north and east, is therefore unable to recurve hurricanes that are moving westward toward the United States thus increasing the probability of landfalls along the Gulf and southeast coasts. Plus you have the subtropical ridge spanned out through the subtropical Atlantic, guess what's gonna happen when a cyclone borders that high? Bingo!

[cycloneye]

TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU AUG 19 2010

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

SHOWERS AND THUNDERSTORMS CONTINUE IN ASSOCIATION WITH A
WESTWARD-MOVING TROPICAL WAVE OVER THE NORTHWESTERN CARIBBEAN SEA.
HOWEVER...NO SIGNIFICANT DEVELOPMENT IS EXPECTED BEFORE THIS SYSTEM
MOVES OVER THE YUCATAN PENINSULA AND CENTRAL AMERICA ON FRIDAY.
THERE IS A LOW CHANCE...10 PERCENT...OF TROPICAL CYCLONE FORMATION
DURING THE NEXT 48 HOURS.

A LARGE AREA OF DISTURBED WEATHER EXTENDS FROM THE WEST COAST OF
AFRICA TO THE SOUTH OF THE CAPE VERDE ISLANDS. THE ASSOCIATED
SHOWER AND THUNDERSTORM ACTIVITY HAS BECOME SLIGHTLY BETTER
ORGANIZED THIS EVENING ABOUT 250 MILES SOUTH-SOUTHWEST OF THE
SOUTHERN CAPE VERDE ISLANDS. ENVIRONMENTAL CONDITIONS APPEAR
FAVORABLE FOR ADDITIONAL SLOW DEVELOPMENT OF THIS SYSTEM AS IT
MOVES WESTWARD AT 5 TO 10 MPH. THERE IS A LOW CHANCE...20
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BEVEN

[srainhoutx]

Those thinking that this will quickly consolidate may be in for a surprise. We are seeing several waves/features coming together. We will likely see several areas in the early stages showing signs of spinup before the main dominate low forms. As wxman57 stated earlier, the Islands (NE) need to pay close attention to developments over the next several days. I too expect a Major Hurricane in the days ahead. Right on cue, it appears things a switching to an active period IMO.

[wxman57]

MiamiHurricanes10, Wxman57 is totally correct, a -ve NAO means low pressures in the subtorpics, whilst a +ve NAO usually means a stronger subtropical high pressure and low pressure further north...

Really though thats far too oversimplifying it, you can have different types of -/+NAO!

Ivanhater, I have few doubts that'd be a major hurricane there...I seriously think we are looking at our first major...and if thats the case...I think with no real ridging anywhere in sight past 45W...I just can't see anything past a possible Bermuda threat.

I suggest you read this...start on page 6.

http://mailer.fsu.edu/~jelsner/PDF/Research/LongLead.pdf

I think there is some confusion as to what this paper is saying. It appears that the author is discussing using the NAO values from October-January of the previous winter to predict landfalls 6 months into the future - the next hurricane season. He says that a weak NAO (negative) in the previous Oct-Jan could lead to high pressure across the western Atlantic basin (+NAO) and less recurving storms in the upcoming hurricane season. He's not saying a current -NAO results in more landfalls.

[wxman57]

Those thinking that this will quickly consolidate may be in for a surprise. We are seeing several waves/features coming together. We will likely see several areas in the early stages showing signs of spinup before the main dominate low forms. As wxman57 stated earlier, the Islands (NE) need to pay close attention to developments over the next several days. I too expect a Major Hurricane in the days ahead. Right on cue, it appears things a switching to an active period IMO.

Yes, several competing areas now, like pre-Alex. Will take a few days to consolidate, but I think it'll be Danielle by Sunday or Monday.

[MiamiHurricanes10]

I think there is some confusion as to what this paper is saying. It appears that the author is discussing using the NAO values from October-January of the previous winter to predict landfalls 6 months into the future - the next hurricane season. He says that a weak NAO (negative) in the previous Oct-Jan could lead to high pressure across the western Atlantic basin (+NAO) and less recurving storms in the upcoming hurricane season. He's not saying a current -NAO results in more landfalls.

No, it is just a normal article that helps to forecast what would happen 6 months in advance, it has nothing to so with what is going to happen in the 2011 season.

Anyways, why would that negative NAO be any different to this one?

[gatorcane]

IMO, I think the northern leewards had better watch this extremely closely...

it seems that is the message nearly every time there is a system brewing in the Mean Development region. But no matter how far south it is or what time of year it is, throughs (i.e. weaknesses or holes in the subtropical ridge) can scoop them up, as was the case with Colin which started out at a very low lattitude and ended up comfortably missing the islands to the NE. In this case, the best models we have show this system missing to the NE and run-after-run they show this. Right now I wouldn't be that worried until I saw the GFS or ECMWF show something that gets close.

[KWT]

I suggest you read this...start on page 6.

http://mailer.fsu.edu/~jelsner/PDF/Research/LongLead.pdf

Not sure that paper really proves anything, all it suggests is the Oct-Jan NAO can lead to some sort of influence on the hurricane season in the future...thats nothing to do with the *current* NAO set-up and the tracks.

Look at this map and you'll see what I mean, note the troughing is stronger on the -ve NAO:

http://airmap.unh.edu/graphics/nao_fig_4.jpg
http://www.ncdc.noaa.gov/paleo/ctl/images/nao.jpg
http://www.sott.net/image/image/14891/full/NAO.jpg

Whilst thats for the winter, a strong summer -ve NAO will produce a similar result...

Think about it this way, the +ve NAO leads to one stronger subtropical high usually, esp by September/October time whilst a -ve NAO leads to more frequant troughing however its never quite that clear cut!

[MiamiHurricanes10]

KWT,

You're missing the point. Disregard what time it has, instead look at what a negative NAO entitles.

[cycloneye]

Aric, what do you think about this?

[cycloneye]

Very interesting ITCZ paragraph at 8 PM TWD.

http://www.nhc.noaa.gov/text/refresh/MI ... 2349.shtml?

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 13N38W 11N47W 13N55W. EAST OF THE
TROPICAL WAVE BETWEEN 33W-38W...A MONSOONAL TROUGH IS ANALYZED
AS A SURFACE TROUGH IN PLACE OF THE ITCZ FROM EASTERN MAURITANIA
NEAR 19N06W TO THE W AFRICA COAST NEAR 14N17W AND INTO THE E
ATLC TO 13N27W. THIS MONSOONAL TROUGH HAS PERSISTED OVER THE
PAST FEW DAYS WITH WESTERLY LOW-LEVEL FLOW OBSERVED S OF 13N. AN
EARLIER MORNING ASCAT PASS AROUND 19/1054 UTC INDICATED THE
BEGINNINGS OF A BROAD LOW-LEVEL CIRCULATION SW OF THE CAPE VERDE
ISLANDS NEAR 13N26W. SCATTERED MODERATE AND ISOLATED STRONG
CONVECTION REMAINS UNORGANIZED AND FOCUSED IN THE VICINITY OF
THIS MONSOONAL TROUGH FROM 08N-14N BETWEEN 16W-30W. ELSEWHERE...
SCATTERED MODERATE CONVECTION IS S OF THE ITCZ AXIS FROM 04N-11N
BETWEEN 30W-39W.

[SETXWXLADY]

KWT,

You're missing the point. Disregard what time it has, instead look at what a negative NAO entitles.

I wish I could help. Lol. The easiest way I've heard it put is "Don't confuse stronger ridging with more ridging."