Tropical Wave (Pouch 12L) E Atlantic - (Is Invest 98L)

[MiamiensisWx]

Note: I am starting this thread separate from the models thread because the time frame and suspected system are rather concrete. I am looking at a possible cyclone developing in the 24-26 July time frame.

This is rather in the long range, but the agreement among the "reputable" models is surprisingly solid. The ECMWF, the GFS, and the GEFS (GFS ensembles?) all agree that the MJO will retrograde toward Phases 1/2 within the next week, with the reliable ECMWF leaning toward Phase 2. This causes enhanced environmental vorticity to develop as the African monsoonal jet (day eight and beyond) begins to expand west into the eastern Atlantic. In this time frame (probably 24-26 July, as the GFS is usually too fast with this kind of pattern shift), the ECMWF develops a split flow over Greenland and begins to hint at an MJO-induced pattern change, with the +NAO that has persisted for three months finally shifting into a neutral and then a likely -NAO regime heading into early August. This would tend to allow lower pressures and weaker trades in the MDR as the whole mid-level pattern retrogrades west: first the Bermuda High shifts west (retrogrades) toward the Southeast, then the trough over the East Coast moves inland into the Upper Midwest yet again. This not only means better conditions for Cape Verde development--reduced trades = weaker low-level shear, less stable air (=less of an inversion) in the mid-troposphere--but also signals an increased risk of landfalls with any Cape Verde system that does not recurve immediately. In fact, as early as 22 July, the GFS continues to indicate development with a tropical wave that moves off the African coast. Until today, the GFS had been showing this feature on an on-again, off-again basis, usually only to shunt the prospects back into the misty long range, but this time it has moved the time frame a bit closer; and while it is probably too rapid with development, its general idea is close in time frame to that of the more-reliable ECMWF, which shows a similar situation emerging. The general idea is that there is a chance that one of the tropical waves coming off W Africa may attempt to form in the 24-26 July time scale, when the pattern shift kicks in. I think this is worth watching because the long-range GFS has continuously brought this proposed system very far to the west, reaching the Caribbean in about two weeks. The upcoming pattern will support a westward track with any feature that develops in the MDR circa 24-26 July. This definitely bears watching as this potential system would impact the Caribbean by the first week of August, when seasonal conditions start to become more favorable than in July.

ECMWF long range

GFS day six

ECMWF MJO forecast
GEFS MJO forecast

[cycloneye]

Here is the wave in East Africa at 18:00 UTC.

[Gustywind]

Nice sat pic showing nicely the twave. Good job as... usual Cycloneye

[Cyclenall]

What a disappointment this July has been, and no responses of "its July" please.

In conjunction with MiamiensisWx's post, I was wondering how closely linked the NAO and Bermuda High is together. What has confused me a bit is how there is great ridging in the western Atlantic for storms to move westwards (Bermuda High) but yet too overbearing for good TC formation (Chantal) because of fast movement and dry air. The opposite would be weaker Bermuda High and more favorable conditions but then they wouldn't always go westwards and might move north. How do you get that combo of westwards into the SE US and very favorable? The answer would be MiamiensisWx's last part of the NAO shifting but because I don't know how it actually causes those favorable effects, I always think of the Bermuda High causing that. Does the NAO control the BH or is it something else (eg. 500 mb pattern, temperature, etc.)?

[JonathanBelles]

What a disappointment this July has been, and no responses of "its July" please.

In conjunction with MiamiensisWx's post, I was wondering how closely linked the NAO and Bermuda High is together. What has confused me a bit is how there is great ridging in the western Atlantic for storms to move westwards (Bermuda High) but yet too overbearing for good TC formation (Chantal) because of fast movement and dry air. The opposite would be weaker Bermuda High and more favorable conditions but then they wouldn't always go westwards and might move north. How do you get that combo of westwards into the SE US and very favorable? The answer would be MiamiensisWx's last part of the NAO shifting but because I don't know how it actually causes those favorable effects, I always think of the Bermuda High causing that. Does the NAO control the BH or is it something else (eg. 500 mb pattern, temperature, etc.)?

So, it's been a disappointing July because nothing has hit the SE US? I'll take a dead Chantal or a bunch of fish any day of the year over a hurricane on my doorstep. Keep up the unfavorability through November and i'd be happy.

[Hurricane Alexis]

What a disappointment this July has been, and no responses of "its July" please.

In conjunction with MiamiensisWx's post, I was wondering how closely linked the NAO and Bermuda High is together. What has confused me a bit is how there is great ridging in the western Atlantic for storms to move westwards (Bermuda High) but yet too overbearing for good TC formation (Chantal) because of fast movement and dry air. The opposite would be weaker Bermuda High and more favorable conditions but then they wouldn't always go westwards and might move north. How do you get that combo of westwards into the SE US and very favorable? The answer would be MiamiensisWx's last part of the NAO shifting but because I don't know how it actually causes those favorable effects, I always think of the Bermuda High causing that. Does the NAO control the BH or is it something else (eg. 500 mb pattern, temperature, etc.)?

The "it's July" responses are correct. Climatology says the Atlantic only sees 1 storm in July, so far that's what we've had. I don't know what your expectations for July are, cause mine aren't high.

[Cyclenall]

The "it's July" responses are correct. Climatology says the Atlantic only sees 1 storm in July, so far that's what we've had. I don't know what your expectations for July are, cause mine aren't high.

My expectations were high for this July, I predicted a busy mid-July period. Ask me the same during 2012, I would be standing right next to you and others.

[SouthFloridawx]

Miami, we will see if your hypothesis works out. Keep us updated as time goes on. Awesome research by the way!

[Hurricaneman]

The 12zGFS shows development by 228hrs in the same area so at least it seems to be consistent in that, but after that is a guess depending on the trade winds and how the ridge\troughs are oriented

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products

[RL3AO]

You know its slow when we're tracking waves closer to the Indian Ocean than the Atlantic.

[Blown Away]

12z develops brings our "bear" to PR again and 06z recurved it in central Atlantic.

[Blown Away]

Tracks of all storms that reached hurricane strength in July (52):


Tracks of all storms that reached hurricane strength in August (224):


Whether we like it or not, the switch almost always flips in August and boom!

[CalmBeforeStorm]

Whether we like it or not, the switch almost always flips in August and boom!

And I would bet the large majority of those storms in July were in the later portions of the month. Early and mid July are usually dead. Chantal was very much the exception to the rule. Also, July activity has very little to do with whether the August/September season is active or not.

[Hurricaneman]

Whether we like it or not, the switch almost always flips in August and boom!

And I would bet the large majority of those storms in July were in the later portions of the month. Early and mid July are usually dead. Chantal was very much the exception to the rule. Also, July activity has very little to do with whether the August/September season is active or not.

I looked at the map for July and did anyone notice that the eastern most 2 are both named Bertha one from 1996 and the other from 2008

On topic: the wave that the models develop is looking pretty healthy as it moves towards central Africa so I guess they're expecting the wave to gain organization as it tracks west

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products

[blp]

Euro looks to be showing the low that the GFS has been developing off and on. I really miss the higher resolution Euro pics from Huffman's site

[MiamiensisWx]

And I would bet the large majority of those storms in July were in the later portions of the month. Early and mid July are usually dead. Chantal was very much the exception to the rule.

Indeed, you are correct. Since 1851, four storms in July have formed within 530 miles of the Cape Verde islands: Anna 1969, César 1990, Alex 1998, and Bertha 2008. The first three of these, 75%, formed on or after 25 July. Of all July storms (113) basin-wide, 28 (24.8%), or nearly one-fourth, of them formed on or after 25 July. That is a very hefty proportion of all known July cyclones, further providing evidence that the month usually features, on average, one or two storms--a tiny number compared to that in August, September, or October. Usually, July is also the earliest month to see the first named storm (1966-present); see the NHC climatology page. So far, we have already seen three named storms as of 08 July 2013, so we are more than 2:1 above average.

Storms that formed on or after 25 July:


As for the possible system, the fact that the ECMWF shows development south of the Cape Verde islands beginning on 26 July is significant. Usually, the ECMWF is more conservative in regard to development, so the GFS--which, as usual, has been showing this development consistently for more than a week--while usually the first model to hint at development, is usually too fast with the timing. The ECMWF tends to reflect the timing better; and once it and the GFS align (as the 12Z GFS does by delaying development until 26 July, when the ECMWF now starts to show development), the plausibility of development increases substantially. Coupled with the expected pattern shift, the signal for TC formation off W Africa beginning on 26 July is increasing.

[cycloneye]

Another GFS run (18z) continues with it but look at it

[MiamiensisWx]

Another GFS run (18z) continues with it but look at it

Where can I find that full-resolution graphic showing the surface pressure? I looked at Levi's Web site but cannot find the graphic which you posted.

[cycloneye]

Another GFS run (18z) continues with it but look at it

http://oi40.tinypic.com/w2fz9i.jpg

Where can I find that full-resolution graphic showing the surface pressure? I looked at Levi's Web site but cannot find the graphic which you posted.

Here it is. Go to surface pressure & 10M Wind Speed.

http://www.tropicaltidbits.com/analysis ... 013071718/

[SouthFloridawx]

Hey Miami, I think you should check this out.

CFS (Climate Forecast System); 1.0°×1.0° forecast grid
500mb GPH Anomaly (5-day Averages)

http://www.tropicaltidbits.com/analysis/models/cfs-avg/2013071706/cfs-avg_z500a5d_atl.html

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