Two African waves, 92L and 93L, worth watching

By: Dr. Jeff Masters , 2:59 PM GMT on August 11, 2011

Share this Blog
16
+

An African wave is near 13°N 35°W, about 700 miles west-southwest of the Cape Verde Islands. This system, (Invest 92L), is moving west to west-northwest at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands early next week. Recent visible satellite loops show that 92L has less heavy thunderstorm activity near where it is trying to develop its circulation center than yesterday. Water vapor satellite loops that a large area of dry air lies just to the west of 92L, but the atmosphere in the immediate vicinity of 92L is moist. Even so, the decline of heavy thunderstorm activity since yesterday implies that dry air is probably working its way into 92L. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 15 knots affecting 92L. Sea surface temperatures are 26.5° - 27°C, which is very close to the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Morning satellite photo of Invest 92L and Invest 93L.

Forecast for 92L
Low to moderate wind shear of 5 - 15 knots is predicted along 92L's path over the coming three days, which should allow the storm to organize, assuming it can shut out any incursions of dry air that might intrude. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show weak development or no development of 92L, and NHC gave 92L a 30% chance of developing into a tropical depression by Saturday morning in their 8am outlook. A steady west to west-northwest motion for 92L is predicted by all of the models, which would put the storm in the vicinity of the northern Lesser Antilles Islands by Sunday. On Saturday and Sunday, 92L is expected to enter a region where an upper-level low pressure system will bring high wind shear of 20 knots to the storm, which should slow development. This upper-level low is also expected to turn 92L more to the northwest, so the storm is likely to pass north of the Lesser Antilles, though may pass close enough to give heavy rains to the northernmost islands. It is too early to know if 92L will recurve out to sea and potentially threaten Bermuda, or continue to the northwest towards the U.S. East Coast.

93L
An African wave that emerged off the coast of Africa is near 10°N 22°W, a few hundred miles south of the Cape Verde Islands. This system, (Invest 93L), is also moving west at 10 - 15 mph, and has the potential to develop into a tropical depression or tropical storm before arriving near the northern Lesser Antilles Islands near the middle of next week. Recent visible satellite loops show that 93L has a decent amount of heavy thunderstorms, but this activity is not well organized. There is not much spin associated with 93L yet. 93L is fairly well-protected from dry air to its north and west. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 20 knots affecting 93L. Sea surface temperatures are 27.5°C, which is one degree above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 93L
Moderate wind shear below 20 knots is predicted along 93L's path over the coming five days, which should allow the storm to steadily organize. 93L is about 600 miles east of 92L, which is close enough that the two systems may interfere with each others' organization. The latest 00Z and 06Z model runs of the four best models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET), have only one model, the GFS, that is indicating significant development of 93L. This model brings 93L near the northern Lesser Antilles Islands by Wednesday. NHC gave 93L a 20% chance of developing into a tropical depression by Saturday morning in their 8am outlook. Due to moister air, the potential for less wind shear, and a more southerly track, 93L is probably a greater threat to the Lesser Antilles than 92L.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 609 - 559

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39Blog Index

Invest 93L is better organized than Invest 92L right now, but it will be interesting to see if it is vice-versa after 92L separates from the ITCZ and begins to sustain itself.

It will be a very close call to see which one becomes a tropical depression, if one or both of them even become a TD.

Member Since: Posts: Comments:
Quoting Levi32:


Yeah it's gone on this run.


and 93L looks poised to follow a similar route

Member Since: Posts: Comments:
Quoting FLWxChaser:


Agreed. Interesting flip flops in days ahead I'm sure.


Yep... if you don't like a run... just wait for the next one. ;-)
Member Since: Posts: Comments:
Quoting USAFwxguy:
Without building high to the north, 92L should just track the periphery of the Bermuda high to its east, likely to spare CONUS on this run. Unless we see that high come over top in future frames.



Agreed. Interesting flip flops in days ahead I'm sure.
Member Since: Posts: Comments:
.
Member Since: Posts: Comments:
Complete Update

Hey Boys & Girls... can you say Choo Choo train

TS BUSTED FORECAST ALIBI






Member Since: Posts: Comments:
Quoting BahaHurican:
Geez. I wonder what they'd do to a customer who asks for it then doesn't drink it....


The waiter probably gulps it down quick to avoid the $500 fine
Member Since: Posts: Comments:
Quoting USAFwxguy:
Without building high to the north, 92L should just track the periphery of the Bermuda high to its east, likely to spare CONUS on this run. Unless we see that high come over top in future frames.



Yeah it's gone on this run.
Member Since: Posts: Comments:
Quoting BahaHurican:
For a minute there I thought I was the only one saw that....

These model runs are not looking for Central America and the Yucatan, folks. I'd say anybody from Barbados [well, a bit low] north to Nova Scotia needs to have whatever hurricane plan in place. Sure not the year to not have stuff ready.... Looks like we're going to have some interesting trough action, enough to have a wide range of possible influences on track.

That's really what I'm taking away from the "interesting" variations in long-range model tracks...


I would say as far north as Newfoundland. They took a bad hit last year from Ivan, worse than Nova Scotia got from Earl.
Member Since: Posts: Comments:
my money is on our local weather people here in florida and they just said again at 6pm 92 and 93 will go out to sea if not fizzle out
Member Since: Posts: Comments:
598. beell
Get your bets down soon. Only 40 or 50 model runs remaining!
Member Since: Posts: Comments:
Quoting BahaHurican:
For a minute there I thought I was the only one saw that....

These model runs are not looking for Central America and the Yucatan, folks. I'd say anybody from Barbados [well, a bit low] north to Nova Scotia needs to have whatever hurricane plan in place. Sure not the year to not have stuff ready.... Looks like we're going to have some interesting trough action, enough to have a wide range of possible influences on track.

That's really what I'm taking away from the "interesting" variations in long-range model tracks...


LOL...what you call variations I call torture...these early model runs annoy me...LOL
Member Since: Posts: Comments:
fail


Member Since: Posts: Comments:
Quoting reedzone:


Excellent analysis :)



Thanks. I can't post graphics anymore because I had to leave for dinner
Member Since: June 7, 2007 Posts: 4 Comments: 962
Quoting bluenosedave:


Direct hit on Cape Breton. Yuck. Earl volume II.
For a minute there I thought I was the only one saw that....

These model runs are not looking for Central America and the Yucatan, folks. I'd say anybody from Barbados [well, a bit low] north to Nova Scotia needs to have whatever hurricane plan in place. Sure not the year to not have stuff ready.... Looks like we're going to have some interesting trough action, enough to have a wide range of possible influences on track.

That's really what I'm taking away from the "interesting" variations in long-range model tracks...
Member Since: Posts: Comments:
Quoting NCHurricane2009:


Is is true the enhanced precipitation over Sahel and eastern Atlantic is because the waves get stronger from such a pattern? Do cooler Guneia SSTs promote a stronger African Easterly Jet at the mid-levels, hence enhancing the tropical waves?


I'm not Levi, but

First question, not necessarily. More rain over the Sahel usually implies a stronger pressure gradient between the Saharan heat low and the relatively higher pressures over the Gulf of Guinea to the south. This draws the monsoon trough further north. A stronger pressure gradient does tend to produce a stronger AEJ and monsoon trough, which in turn would strengthen the waves coming off Africa...so more rain over the Sahel can imply stronger waves over Africa, however, it isn't necessarily the result of stronger waves.

Second question, yes.
Member Since: Posts: Comments:
Great Lakes low may allow for 92L to gain some latitude

Member Since: Posts: Comments:
To Comment 583...

Neat...thanks for the tips...I'll have to try looking at 93L on satellite imagery...for now I have the crummy E Atlantic views on the NHC webpage that update every few hours instead of minutes.
Member Since: Posts: Comments:
92L should stay below that 1016 isobar, roughly, so this run may take it to FL coast, perhaps SC.

Member Since: Posts: Comments:
Quoting Twinkster:
18z



12z




93L and 92L reversed strengths because of orientation of high and also trough lifting out much more quickly this run


Excellent analysis :)
Member Since: Posts: Comments:



talk about high pressure
Member Since: June 7, 2007 Posts: 4 Comments: 962



not looking good for east coast
Member Since: June 7, 2007 Posts: 4 Comments: 962
Quoting brazocane:
This is an example of how dry it is here in League City Texas:

7. All restaurants are prohibited from serving water to patrons except upon request of the patron


FORT WORTH, TEXAS—In parched Texas, it's often easier to drill for oil than to find new sources of water.

So after years of diminishing water supplies made even worse by the second-most severe drought in state history, some communities are resorting to a plan that might have seemed absurd a generation ago: turning sewage into drinking water.

Construction recently began on a $13 million water-reclamation plant believed to be the first in Texas. And officials have worked to dispel any fears that people will be drinking their neighbours' urine, promising the system will yield clean, safe water. Some residents are prepared to put aside any squeamishness if it means having an abundant water supply.

"Any water is good water, as far as I'm concerned," said Gary Fuqua, city manager in Big Spring, which will join the cities of Midland, Odesa and Stanton in using the water.

When the water finally reaches the tap, Fuqua said, its origin is "something I wouldn't think about at all."

Similar plants have been operating for years in Arizona, parts of California and in other countries. Water experts predict other American cities will follow suit as they confront growing populations, drought and other issues.

"It's happening all over the world," said Wade Miller, executive director of the WateReuse Association based outside Washington. "In some places . . . resources are down to very low levels, and this is one of the few resources available."

The Colorado River Municipal Water District in West Texas began considering a wastewater recycling plant back in 2000 and broke ground last month on the facility in Big Spring, about 160 kilometres southeast of Lubbock. When finished late next year, it should supply 7.5 million litres of water a day.

The timing couldn't be better. This year's drought has made a bone-dry region even drier, causing crops to wither and animals and fish to die off by the thousands.

At least one of the three reservoirs in West Texas may dry up if the drought persists through next year, as climatologists have predicted could happen. That means the district's water supply could be reduced from 246 million litres a day to 170 million litres, said John Grant, the water district's general manager.

"We have limited water supplies in Texas, and you have to turn to other sources of water," Grant said.

The new system could actually improve the taste of the region's water by removing the minerals and salt that give it a distinctive briny flavour, he added.

The idea to recycle sewage isn't new. Fort Worth and other cities across the nation have long used treated wastewater to water grass and trees and irrigate crops.

Astronauts aboard the International Space Station have been drinking recycled urine and sweat since 2009 — and consistently given the water good reviews.

For years, NASA had been working on equipment that would enable astronauts to recycle their wastewater for drinking, cooking and bathing. The system was launched to the space station in late 2008, and it took several months to conduct enough tests — in orbit and on the ground — to ensure the water was safe to consume.

Since the space-shuttle fleet was retired last month, the space-station's recycling system is needed more than ever. Shuttles can't deliver fresh water, and the agency says astronauts will need such recycling systems on future missions to an asteroid and Mars.

Still, the slightest suggestion of urine in drinking water can make people uneasy.

In June, officials in Portland, Ore., sent 30 million litres of treated drinking water down the drain after a man was caught on a security camera urinating into a reservoir. City leaders said they didn't want to distribute water laced, however infinitesimally, with urine.

The wastewater-recycling process is long and complex. The first steps remove salt and impurities, such as viruses and even traces of medicine. Then the wastewater is channelled into a lake or reservoir, where it's blended with fresh water and eventually gets pumped into a water-treatment facility. There, it undergoes several more rounds of cleaning, disinfection and testing before finally reaching home faucets.

When the project was presented several years ago, there were no major protests during public hearings, Grant said. Most people don't mind the idea once they understand that the treated water is safe to drink, he said.

"Folks out here have accepted it because they understand what the value of water is," Grant said.

In California, the West Basin Municipal Water District in southwest Los Angeles County started treating wastewater in the 1990s because it had been importing 80 per cent of its water. Using recycled water has not only cut down on importing costs but also helped the environment by eliminating the need to dump sewage in the ocean, officials said.

In Orange County, Calif., a similar project started several years ago now provides 265 million litres a day, water that is considered nearly as pure as distilled, Miller said.

Member Since: Posts: Comments:
18z



12z




93L and 92L reversed strengths because of orientation of high and also trough lifting out much more quickly this run
Member Since: June 7, 2007 Posts: 4 Comments: 962
Quoting NCHurricane2009:


How can you tell if a system is integrated into the ITCZ versus not? Aren't tropical waves low pressure areas already seperate from the ITCZ at their inception?



No, not necessarily. Often their signature on satellite imagery over the eastern Atlantic is a "buckle" in the ITCZ itself. It takes some experience with satellite imagery to tell for sure if something is integrated into the ITCZ or not, but it actually isn't that hard. The ITCZ is usually fairly visible as a line of thunderstorms, and if you see a buckle in it without much going on north of that buckle, then it's a good bet that the wave is literally a wave in the ITCZ. If pronounced low-level turning exists, with or without convection, well to the north of the ITCZ boundary, then the wave may be partially or fully separated. Typically they do not fully dissociate until they get west of 40W.

With 93L, the blob associated with it is clearly along the monsoon trough boundary of thunderstorms and converging surface winds trailing both west and east of it. Thus, it is not a separated entity yet. This is bad for it because the ITCZ is a broad boundary of convergence, making it hard for 93L to "hog" the convergence for itself, which is what it wants to develop. If it separates, that task becomes easier, as long as dry air doesn't immediately surround it after it leaves the shelter of the moist ITCZ.
Member Since: Posts: Comments:
Quoting Levi32:


Yes. It will have an effect on something no matter what. The typical signals of its presence seem to be showing up, with above-normal precipitation in the western Sahel and eastern Atlantic, and below-normal precipitation just to the south along the African coastdue to the cooler water promoting subsidence, pushing the monsoon trough farther northward than normal.



Thank you and NChurricane2009 for the explanation. It looks like many long nights of model watching from where I am.
Member Since: April 29, 2009 Posts: 75 Comments: 14549
Looks as if trough to recurve 92L may be lifting out a bit quicker on 18z

12Z


18Z


92L may make it a bit further west with this run, compared to last.

The 1010 isobar over the east coast is a good frame of reference.
Member Since: Posts: Comments:
Quoting Levi32:


Yes. It will have an effect on something no matter what. The typical signals of its presence seem to be showing up, with above-normal precipitation in the western Sahel and eastern Atlantic, and below-normal precipitation just to the south along the African coastdue to the cooler water promoting subsidence, pushing the monsoon trough farther northward than normal.



Is is true the enhanced precipitation over Sahel and eastern Atlantic is because the waves get stronger from such a pattern? Do cooler Guneia SSTs promote a stronger African Easterly Jet at the mid-levels, hence enhancing the tropical waves?
Member Since: Posts: Comments:



trough already lifting out
Member Since: June 7, 2007 Posts: 4 Comments: 962
1 month to the maybe happiest anniversary to the 9/11 attacks, because Ding dong Bin Laden's dead!
Member Since: Posts: Comments:
Quoting beell:
Regardless of your views on a warming planet, your gas and electric companies are making long-ranges plans to restructure their rate programs to stabilize revenue.

A quick off-topic look at "decoupling". Where rates are dependant on customer base-not product sold or how efficient they operate and in part, a way to make up for conservation gains and energy efficiency.

How ironic. This ain't AGW, this is bizness.

Pew Center Overview - "Decoupling"


So are the oil and coal companies, They are spreading this propaganda merely to keep their profits up for as
possible. I grew up in Eastern Kentucky. They wrecked a natural paradise and left behind a population of meth heads watching Fox.
Member Since: Posts: Comments:
Quoting Twinkster:



trough weaker and further north in 18z run


Notice it's well south of Bermuda at that time.. Probably a scare for the East Coast on this run.
Member Since: Posts: Comments:
574. MTWX
Update on TX drought.


Link
Member Since: Posts: Comments:
Quoting BahaHurican:
!!! Was that a Canada hit I saw at the end of that run???


Direct hit on Cape Breton. Yuck. Earl volume II.
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:


yep gates are opening



Nice.

Ship it!
Member Since: Posts: Comments:
Quoting BahaHurican:
Geez. I wonder what they'd do to a customer who asks for it then doesn't drink it....


In the casinos in Vegas, when you ask for water, they bring you one of those dinky half-size bottles!!! Talk about conservation!
Member Since: Posts: Comments:
Quoting brazocane:
This is an example of how dry it is here in League City Texas:

7. All restaurants are prohibited from serving water to patrons except upon request of the patron


All the places I've dined this has been the norm for a number of years.
Member Since: Posts: Comments:



trough weaker and further north in 18z run
Member Since: June 7, 2007 Posts: 4 Comments: 962
im still holding on to my prediction and that neither 92 nor 93 will amount to much or just plain out stay out to sea we will see i will admit my prediction got some help from the local weather channles here in florida who are all saying they shouldnt be a concern for the east coast with the front dropping down by the end of next week and should keep everything away
Member Since: Posts: Comments:
Quoting Tropicsweatherpr:
Levi, has the cooling of the Gulf of Guinea having already an effect in what is going on in the Eastern Atlantic?



Yes. It will have an effect on something no matter what. The typical signals of its presence seem to be showing up, with above-normal precipitation in the western Sahel and eastern Atlantic, and below-normal precipitation just to the south along the African coastdue to the cooler water promoting subsidence, pushing the monsoon trough farther northward than normal.

Member Since: Posts: Comments:
Quoting FLdewey:
Two oranges and a yeller... interesting.


yep gates are opening

Member Since: Posts: Comments:
Quoting brazocane:
This is an example of how dry it is here in League City Texas:

7. All restaurants are prohibited from serving water to patrons except upon request of the patron
Geez. I wonder what they'd do to a customer who asks for it then doesn't drink it....
Member Since: Posts: Comments:
Quoting Tropicsweatherpr:
Levi, has the cooling of the Gulf of Guinea having already an effect in what is going on in the Eastern Atlantic?



Surface temperature contrasts lead to upper-level wind jets. If the Gulf of Guniea is cooler, there is more temp contrast at the low-levels relative to the hotter Saharan Africa to the north. This enhances the African Easterly Jet, which is responsible for the genesis of tropical waves.

I think Levi could probably answer this better than I can, that's why you asked him :)

Member Since: Posts: Comments:
Afternoon everyone, just stopping by for a little. I see we still have 92L and 93L. These two will probably be with us for the next week and a half as they take their time crossing the Atlantic.

92L Current Analysis and Forecasted Environmental Conditions

92L isn't looking all that impressive at the moment. Some scattered convection, but it remains far removed from the broad, weak low level circulation (which may be closed, but if it is, it's a very weak closure). Dry air, subsidence to the west and north (in response to the ridge and TUTT), marginal SST temps, the broad nature of the wave, and dmin are the biggest factors I can think of as far as explaining the lack of convection over the LLC. As a result of the lack of convection, the LLC remains weak, possibly open, and there is minimal surface convergence occurring. No mid level circulation is present over 92L, either. Both of these are a result of a lack of convection, but they also feedback and allow convection to continue. So it goes to show that convection over the center is not very favorable right now. As 92L heads west, dry air and subsidence from the ridge to the NW and the TUTT will remain an issue for the next 3/4 days. Upper convergence and shear will also kick up over the weekend as 92L passes the TUTT axis. After that, by next week, shear will drop some and upper convergence will as well as 92L passes the TUTT and is ventilated by the trough off the east coast. As a result, I wouldn't be surprised if this doesn't develop over the next few days. As it passes north of the Caribbean by next week it will have a more favorable environment, but development is still no guarantee.

93L Current Analysis and Forecasted Environmental Conditions

It's hard to know what is going on at the surface of 93L, but according to CIMSS analysis, there is a lot more low level convergence occurring with 93L (as opposed to 92L). This is supported by the stronger and more focused convection. Also seeing a stronger, more centralized vort signature (you can't see 93L on the CIMSS 850 mb vort analysis, this observation was based off model intializations), and there is a much stronger mid level circulation over the system as opposed to 92L. This system also has lighter trades, warmer SSTs, and no ridge to the NW producing subsidence and dry air out in front of it like 92L has. Over the next several days, 93L will have a nice moist environment ahead of it thanks to 92L clearing the way. However, this does not necessarily mean that 92L will intensify. Shear and upper divergence will become pretty unfavorable from Sat-Tue in response to the TUTT and potential outflow from 92L. As a result, no significant development should occur with 93L over the next few days. By the middle of next week, however, shear and upper divergence are expected to become much more favorable for development as 93L passes the TUTT.

Track

Looking ahead with these two, re-curvature looks to be quite likely for 92L, after it continues its WNW track north of the Caribbean. Bermuda, the northern eastern Caribbean islands, and the East Coast of the US and Canada should still keep there eyes on this one before writing it off. 93L's track is a lot more uncertain at the moment, because it is still a long ways out. This system will be with us for about the next week and a half, so there is no need to get too worried about track forecast at the moment. NE Caribbean islands should watch it for now, but as far as continental US, Bahamas, and Bermuda, I wouldn't get too into the track forecasts at the moment. It's a very long ways out (beyond a week).


MJO

At the moment the Madden-Jullian Oscillation is very weak and isn't really centered over any specific basin. However, according to the model consensus, the MJO should be heading our way


GFS Ensembles Biased Corrected




ECMWF Ensembles




UKMET Ensembles




Pretty strong consensus among the global models that the MJO will be returning to our basin right as we head toward the most active part of the season.
Member Since: Posts: Comments:
Quoting brazocane:
This is an example of how dry it is here in League City Texas:

7. All restaurants are prohibited from serving water to patrons except upon request of the patron


Seems this should be policy EVERYWHERE!
Member Since: Posts: Comments:
Quoting depstein:
I'm not that up on meteorology but I know some of you are. Do you think that if invests 92 and 93 develop, we could see the Fujiwara effect?
If not why?
If so, how might this affect the track?
Doubt it, because they're a little far apart each other but.... 93L is moving faster that 92L and they move in the same direction which may happen to form a genetic mutation called.........

FRANKENCANE!
Member Since: Posts: Comments:
560. beell
Regardless of your views on a warming planet, your gas and electric companies are making long-ranges plans to restructure their rate programs to stabilize revenue.

A quick off-topic look at "decoupling". Where rates are dependant on customer base-not product sold or how efficient they operate and in part, a way to make up for conservation gains and energy efficiency.

How ironic. This ain't AGW, this is bizness.

Pew Center Overview - "Decoupling"
Member Since: Posts: Comments:
This is an example of how dry it is here in League City Texas:

7. All restaurants are prohibited from serving water to patrons except upon request of the patron
Member Since: Posts: Comments:

Viewing: 609 - 559

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
47 °F
Overcast