FLHurricane.com: Large Wave East of Caribbean Looking Better this Morning

7:00AM EDT Update 01 August 2011
The first of August has arrived, and most attention in the Atlantic is on the wave east of the Caribbean, that did a split yesterday, but is now coming together. The eastern area from yesterday started to get its act together overnight, and now seems ready for a development run.

Because of the relatively large size of the wave, any development is expected to continue to be slow, but probably steady. Those in the Leeward islands will probably get Tropical Storm force winds and watches/warnings put up when the system gets classified (probably after recon, or by 11AM if the system continues to look good) Barbados would be the first to get the worst of it (the leading rain it got yesterday has disappeared to go back toward the main system)

The wave has a large shield from dry air in the near term, and shear is relatively light, so a steady increase of strength is expected, but not a fast increase because of the size of the area, at least in the near term.

The track gets a bit hairy, I think the models will continue shifting toward the west, at least today, and settle in over a western Hispaniola crossover, which could destroy the system (And probably brings floods Haiti if it does). Once it gets across, as a much weaker system, it will likley stay in the Bahamas, and the game of "when will it turn north" commences. (The most famous case of it for Central Florida was probably Hurricane Floyd). This system (91l)t will likely recurve, but it's too early to say when. Two wildcards are it misses the mountains of Hispaniola, or stays weak and continues further west toward Central America (The longer it does not develop the more the Central America case becomes likely). For more speculation, see the forecast lounge. For the real forecast see the National Hurricane Center when the first advisory comes out, likely today at 11 or later if the storm does not form. Recon is almost in the system right now.

Either way those in the Leewards will need to prepare for a Tropical Storm (if it can get organized enough for it before it reaches there), and the Virgin Islands and Puerto Rico will want to watch local officials/media for what may occur there. And beyond is still really too soon to tell, it all depends on how far west the system is. It has not developed yet, so the models, position, and moment are all to be taken with a grain of salt at the moment. In short really the entire Caribbean from the Leewards up and West, Bahamas, Florida to North Carolina should keep tabs just to see what is going on with the system. It's becoming less of a mess, but it still is just a wave so beware the hype.

5:30PM EDT Update 31 July 2011
The wave 91L is very elongated, and borderline two separate systems. Recon went in the system this afternoon but was unable to find a definite circulation center. It also had communications issues which limited the data coming back.

The National Hurricane Center issued a special Tropical Weather Outlook which includes the entire elongated area (including an oval shaped graphic)

Those in the northern windward and leeward islands should be watching this closely and treating it as a Tropical Storm.

Beyond this it gets very complicated because of the dual vortices, it really depends on where the eventual storm center forms. Models are close to useless in this scenario (pick between the west or east area, the results will be different either way.) While the system remains weak, it is likely to continue due west into the Caribbean.

In short anywhere west of this system needs to check back to see when (and if) this system (or systems) consolidate. This is a pretty unique situation and the models are showing trends if it were to organize (assuming the eastern most).

7AM EDT Update 31 July 2011
The wave east of the Caribbean, referred to as invest 91L, has been slowly organizing since yesterday and the NHC now has it as a 100% chance for development over the next 48 hours (Well as of 2AM). As of 7 AM, it still has not formed. It is likely when recon aircraft enters the area this afternoon it will be upgraded.

This wave is very large, and if it were a bit more spread out may have even been considered two areas, but since they were in close proximity, it's been a slow progression of organization. Those in parts of the Lesser Antilles may expect some sort of Tropical Storm Watch/Warning to be issued today. The system also has a slight bit of dry air intrusion, which will limit how fast strengthening could occur, at least in the next day or two.

Barbados is getting the first part of the rain this morning from the western edge of this broad area.

Model guidance has not been handling this large area well, with initializations (starting positions, and movement) not being very accurate as a generally westward motion has occurred since yesterday. This morning even though multiple guidance has been in fairly good agreement with each other through the first 2 days, it's been consistently off also, on initialization. You have to verify with real observations what the models are and are not doing, especially with weak, broad and large (or very small) systems. The models tend to do best with fairly well organized systems with a solid core (not titled, or sheared). This system is borderline two areas (which is why for Example the Euro/EWMCF model basically splits it), and very broad, and not a good candidate for early model tracking.

What this does is open up a great deal of possibilities once the storm enters the Caribbean, and puts Puerto Rico, Hispaniola, and the Virgin islands needing to watch this (Although it is possible for the system to stay south and enter deeper into the Caribbean, it is not currently the most likely scenario..) We're awaiting official advisories to comment more about this directly, in the meantime check out the Forecast Lounge for more speculation on what may happen, or post if you would like to take a shot at what may occur.

It is very possible because of the split nature of the system, that it may take longer to develop than was anticipated, or keep it from occurring. The "split" nature of this system is very interesting, will one element take over the other, will they literally split into two systems (ala Euro), or will it just keep the whole area weak. Right now, the western 'system' has the better convection but the eastern 'system' has the better circulation, but not a definite low level circulation center yet. Which likely means a generally westward motion for now.

Martinique Radar Recording 91L Approach (flhurricane)

Long term recording of 91L Floater Water Vapor Imagery (flhurricane)

Barbados Brohav Weather Fax

Elsewhere, the cape verde season seems to be starting to get going, as a rather well define wave has exited the African Coastline.

Original Update
Tropical Storm Don, or what little was left of it, made landfall around 9:30 last night, and in the process completely fell apart. Very little rain made it to South Texas, unfortunately.

For those in the northern Leeward islands of the Caribbean, the wave east of you, 91L, looks very likely to develop late today or tomorrow, and overall has a 70% chance for development within a 48 hour period. It appears Tropical Depression 5 or Emily may form later today. Current models are surprisingly aligned, which means the Leewards, Virgin Islands, and Puerto Rico will want to start thinking about preparations if needed.

What may keep it from organizing today is the fast forward motion, but either way the 70% chance for 48 hours seems quite reasonable.

Beyond this, they start to diverge in if it will collide with Hispaniola or miss to the north or south.

Since most speculation on storms before they develop is prone to hype we leave it off the main page, see the Forecast Lounge for more speculation on what may happen, or post if you would like to take a shot at what may occur.

Beyond this, as we enter August we start to enter the busier part of Hurricane season, especially late August. Things may be shaping up for a busy August, but unsure on where the pattern will take most of the systems.

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