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African Tropical Waves 90L and 91L Pose Little Threat

By: Jeff Masters 3:26 PM GMT on September 07, 2014

Two tropical waves spinning off the coast of Africa are worth watching for development, but neither poses a foreseeable threat to any land areas. A tropical wave (90L) located about 700 hundred miles west of the Cape Verde Islands at 10 am EDT on Sunday is headed west to west-northwest at about 10 - 15 mph. Satellite images show 90L has plenty of spin, but heavy thunderstorm activity is limited. The disturbance is embedded in a very dry air mass, has marginal Sea Surface Temperatures (SSTs) of 26.5°C (80°F) beneath it, and is experiencing moderate wind shear. None of our three reliable computer models for predicting tropical storm formation predicts development of 90L over the next five days. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 10%. The wave should pass a few hundred miles northeast of the northern Lesser Antilles Islands on Thursday.


Figure 1. MODIS satellite image of tropical waves 90L and 91L off the coast of Africa at approximately 8 am EDT Sunday September 7, 2014. Image credit: NASA/GSFC.

New African Tropical Wave 91L
A tropical wave (91L) that emerged from the coast of Africa on Sunday is headed west to west-northwest at about 15 mph. Satellite images show 91L has a moderate amount of spin and heavy thunderstorm activity. The disturbance is embedded in a moist air mass, has moderately warm (SSTs) of 27.5°C (82°F) beneath it, and is experiencing moderate wind shear. Two of our three reliable computer models for predicting tropical storm formation predict development of 91L over the next five days. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 30% and 60%, respectively. The wave should take a more northwesterly track by mid-week, and does not appear to be a long-range threat to the Lesser Antilles Islands.

Norbert rapidly weakening
In the Eastern Pacific, Hurricane Norbert weakened to a tropical storm Sunday morning as it moved over cool waters of 25°C (77°F.) Satellite loops on Sunday morning showed that Norbert had lost almost all of its heavy thunderstorms. The current weakening trend should accelerate until Norbert dissipates by Monday. The counter-clockwise flow of air around the hurricane is pulling moisture from the remnants of Tropical Storm Dolly and from the tropical Eastern Pacific northwards into Northern Mexico and the Southern Arizona, and this moisture will be capable of causing flooding rains in those regions.

Jeff Masters

Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

tomorrow the aussie mets will issue their latest ENSO discussion......will be interesting to see if things are trending faster than a winter declaration or on pace as forecast
503. VR46L
Quoting 498. sar2401:


Given the history of African wave invests this season, it seems like the major challenge is getting it past 50W in one piece before any other scenario matters much. :-)


LOL !!! Thats a good point ... I think it will but will head NE shortly after
Quoting 471. wunderkidcayman:

Hey stormwatcher

What's with the "Not WKC"?

LOL. He directed the question to you but I answered and let him know although I am not WKC I answered anyhow.
Quoting 392. ncstorm:

00z CMC never without something to talk about..shows a storm hitting florida and riding up the east coast..the Navgem was showing this scenario a couple of days ago as they both hinted at the area near PR developing as it comes to the SE coast





last frame for the CMC

GOM



Atlantic



Is it trying to develop the upper level low or is this something down the road?

My knowledge of computers is pretty low compared to most of my 80s-90s born peers but what makes the GFS the superior model (most discussions especially on twc and etc may mention the euro but the GFS is the principal one), compared to some of these models showing the Carolinas in the cross-hairs every other week this season?
Quoting 503. VR46L:



LOL !!! Thats a good point ... I think it will but will head NE shortly after


Ok. That is technically two.

Tread lightly.
Quoting 496. HaoleboySurfEC:

I got another fast 1"+ this morning in about 20 minutes. 4AM ish. More to come for the Flo/Dar metropolis (lol). You're up today.

May have to drain some pool water tonight (again). Risky business...hypothermia. Pool temps are dropping below 80F. Here, hold my beer...





I know Darlington/Hartsville/Florence very well..my family is from there..Mothers day is awful in Darlington with the nascar race they have there..we have to detour to get to Hartsville..
Major Flooding being reported in Phoenix, AZ this morning.

I-10 and I-17 both closed in parts due to flooding. Cocorahs.org early reports with 2 to 3 inches overnight for most of the city, and up to 5 in a few areas - still raining too.
Quoting 505. win1gamegiantsplease:



Is it trying to develop the upper level low or is this something down the road?

My knowledge of computers is pretty low compared to most of my 80s-90s born peers but what makes the GFS the superior model (most discussions especially on twc and etc may mention the euro but the GFS is the principal one), compared to some of these models showing the Carolinas in the cross-hairs every other week this season?


The CMC always tries to wipe the Carolinas off the map..every year it tries but fails..it has some type of bias for the east coast, Im thinking because it leads to Canada...one day it may just get it right..
Quoting stoormfury:
WKC I have my reservation about the future track of 91L . looking at the steering currents and a somewhat strengthening of the BH I just cannot see 91L going out to see. my thoughts differ with the GFS and I can foresee a possible threat to the central Antilles.


Yeah but either way too early to speculate at this time right now let's just track it and predict it bit by bit can't go wrong with that so ok for now let's just do between 20W to 30W or 35W
When it reaches that point then we go on to between 30W or 30W to 40W or 45W etc
Quoting stormwatcherCI:
LOL. He directed the question to you but I answered and let him know although I am not WKC I answered anyhow.


Lol ok stormwatcher aka WKC dos . oh (2.0)
I think they're back to two NASCAR races per year starting next April/May and Labor Day weekend. Good for the local businesses. We just stay close to the house or head to the beach. It is quite the spectacle...

Quoting 507. ncstorm:



I know Darlington/Hartsville/Florence very well..my family is from there..Mothers day is awful in Darlington with the nascar race they have there..we have to detour to get to Hartsville..
Quoting 506. FBMinFL:



Ok. That is technically two.

Tread lightly.
give it up dj the FBM OF FLA
Quoting 514. KEEPEROFTHEGATE:

give it up dj the FBM OF FLA


For the life of me I can't figure out what you mean when you talk about this. It is very intriguing, however. I will figure it out eventually. I like a good mystery, but I am at a loss on this one.

It is like I missed an inside joke somewhere.
Bermuda is "Out to Sea"??
Some of you guys don't realize that Bermuda has people as well. 91L is something to watch for Bermuda and the East Coast as reliable models show strong ridging as the system moves west, maybe even dip southwestward in time.
By my definition, if 91L brings sustained gale force winds to Bermuda, it is not a "fish storm", although I guess saying OTS is ok, and that implies missing Caribbean and North America.

People live on Bermuda. GFS says a miss safely East, but GFS seems to often have a slight Northerly (which turns Easterly) bias. Euro is a bit farther West.
Quoting 519. reedzone:

Bermuda is "Out to Sea"??
Some of you guys don't realize that Bermuda has people as well. 91L is something to watch for Bermuda and the East Coast as reliable models show strong ridging as the system moves west, maybe even dip southwestward in time.


Deja vu. Or something. You hit enter a minute before I did...
I think maybe I will just leave for a bit good luck with the blog have fun
Quoting 519. reedzone:

Bermuda is "Out to Sea"??
Some of you guys don't realize that Bermuda has people as well. 91L is something to watch for Bermuda and the East Coast as reliable models show strong ridging as the system moves west, maybe even dip southwestward in time.


Bermuda is out in the sea that the system may go out to. It's a matter of unfortunate geography ... and The Pattern, of course.
Quoting 521. EdMahmoud:



Deja vu. Or something. You hit enter a minute before I did...


I just noticed that!
For all that don't know DR. Rick Knabb is coming down here to see us in Grand Cayman I think he arrives tomorrow

Come to spend time with us as we have our 10 yr anniversary of Hurricane Ivan
Quoting 485. K8eCane:




Wow. Certainly is dark here near the airport


Looked like we were going to have the sun for a little while around 7-8 but nature had other ideas. Worst part of raining off and on at night is the chorus of tree frogs right outside my window when it stops.
The fact that models are not pushing 91L northwest already is a sign that we will be watching this one for a while.
Quoting 529. reedzone:

The fact that models are not pushing 91L northwest already is a sign that we will be watching this one for a while.


I concur. Maybe an East Coast scraper.
Agreed. And by saying this I'm implying that, yes, I believe it will survive it's trek across to the islands.

Quoting 529. reedzone:

The fact that models are not pushing 91L northwest already is a sign that we will be watching this one for a while.
The all-time daily rainfall record in Phoenix, Arizona is 2.91" set in 1933. So far today, they've picked up 2.83", and it's still raining (and will continue to throughout tonight. According to an NWS meteorologist in SoCal, this is a 1-in-200 year rainfall event. In Tuscon, precipitable water value is 2.02", an all-time record, or 206% above average.


@NWSPhoenix
IT'S A RECORD!!! Phoenix Sky Harbor 2.96 in. of rain breaks the all-time calendar day record total previously 2.91/1933. #flood #azwx
It's actually been raining most of this morning. Only enough to get the roads wet, but still - proof that rain can still fall in CA.
Quoting 529. reedzone:

The fact that models are not pushing 91L northwest already is a sign that we will be watching this one for a while.
I still believe that the east coast is about done for any tropical threat.Captain Trough Save the U.S has done it's job well all season long.I don't have any doubt it'll fail now this late in hurricane season..
Wilmington, NC. 74 degrees, feels like 71 degrees. Where was this when it was 90+?
we should be safe unless we get one up our gut. (out of the s carib.) nevertheless heavy rains continue for florida & carolinas
Maricopa County, AZ (Phoenix) - Cocorahs observation network shows that the rain blanketed the entire city and many areas have gotten recordings like the record setting one.

Quoting win1gamegiantsplease:


Is it trying to develop the upper level low or is this something down the road?

My knowledge of computers is pretty low compared to most of my 80s-90s born peers but what makes the GFS the superior model (most discussions especially on twc and etc may mention the euro but the GFS is the principal one), compared to some of these models showing the Carolinas in the cross-hairs every other week this season?
Dr. Masters had a good explanation of the models on Read" target="_blank">his blog last month. The NHC has a review of the the models they use in their FAQ. You can get a basic understanding of the models from these two pages. What it comes down to an individual storm, that's different however. Any of the top four models (GFS, UKMET, ECMWF, and CMC) can do an excellent job on one storm and completely blow it an another. Models also come and go. The NAVGEM, for example is a replacement for the NOGAPS that went operational last year. We don't yet know how well the NAVGEM is going to perform, but the NOGAPS was one of the worst performing dynamical models, so the NAVGEM should be taken with a grain of salt until we have at least three years worth of verification. Even though you see the NAM model being used here, it is not used operationally by the NHC for tropical storms.

The bottom line is that what any individual model predicts more than five days out is virtually meaningless for track. It's completely meaningless for intensity. The average errors are so large that you can flip a coin and be about as accurate. Closer that five days, the ensemble versions of the major models get more accurate but individual models can still be far off. We saw this with the flip-flopping model tracks and Cristobal. It's when the models start to come into agreement that we can get some confidence in their forecasts. Even then, there will still an outlier. In general, the outlier is always wrong, especially when a storm is three days or less from landfall. The most accurate track model is still the NHC official (OFCL) forecast. You won't go far wrong by paying attention to that and ignoring individual models at three days or less out. Model runs for storms 10 days out are strictly for entertainment value.
Although it's only September 8th, winter will be here before you know it, as it appears to have already started it's slow & punctuated push southeastward through North America with snow currently falling in & around Edmonton, Alberta...
Quoting TropicalAnalystwx13:
@NWSPhoenix
IT'S A RECORD!!! Phoenix Sky Harbor 2.96 in. of rain breaks the all-time calendar day record total previously 2.91/1933. #flood #azwx
Phoenix is going to be a wreck. None of their storm systems are set up to handle this much rain, and parts of Phoenix have been built directly in historical washes and arroyos. A normal monsoon type thunderstorm dropping an inch or so of rain causes problems. This is going to be a big deal.
91L is tracking along nicely and is showing signs of slow organisation
Technically any storm that forms and eventually heads out into the Atlantic Ocean is considered out to sea although term should really be "Out To Ocean"

For example 2005

Hurricane Wilma out to sea

TS Franklin out to sea

Hurricane Ophelia out to sea

TS Alpha out to sea

These storms are all out to sea but they still had land impacts

Now fish storms on the other hand

Fish Storm: (Noun) a Tropical Cyclone that forms, develops, peaks, weakens, and dissipates without affecting any land masses at any point, whether direct or indirect. The only effects is on marine areas and ships.

Whatever does form will definately head OTS by the looks of this weekend's trough!
San Diego is up to 58 storm reports now. Most are flooding in Riverside.

There has been a few MESONET reports of more than 1 1/2" of rain in less than an hour this morning. Moisture still streaming up on radar from Norbert's influence..
Quoting 537. washingtonian115:

I still believe that the east coast is about done for any tropical threat.Captain Trough Save the U.S has done it's job well all season long.I don't have any doubt it'll fail now this late in hurricane season..


A second and much more threatening trough effect is to steer any tropical cyclone ahead of it rapidly northward. Hazel is an example of this. A fast moving storm will not have time to lose much intensity before reaching the DC area and that's the easiest way to get true hurricane conditions over the DC area. A deep moderate length trough of the sort that's very common in late September through October, could do this. A short wave within the trough could also enhance TC deepening for a few hours.

I always hope "not this year". Sooner or later my hopes will be dashed.




This is just my opinion. I just really don't think where gonna see much this year. From all the reading I do on here everyday there is something going on out there in the ATL just not letting these tropical waves get there act together. It's been SAL and Shear, dry air. I hate to say it but I really think the season is over with the hostile atmosphere and all. I mean I love tracking them and they head out to sea that is all great. We just have another Hurricane Season with out damage, death, destruction. And I think that is just wonderful.

Sheri
This is the area to watch above PR. These homegrown systems spin up quickly. I was posting this last night, but no takers.


It's depressing



Here's reports from Tally (about GA)..

Storm reports out of JAX covers the homes flooding in Lake City, parts of I-10 are closed.. Over 10" has been recorded as fallen in Lake City..
Those negative tilt troughs of October can capture something from the Caribbean and drag it up the East Coast.

And I mentioned 1985 and November's Hurricane Kate in November.

Sure the season is lame, but one major hurricane that produces quality YouTubes hitting Florida, the Carolinas or Northeast can still make it a season to remember. Even in October. Or November. A high end Cat 2 that does damage in Florida's capitol? That'd be huge.


Nearer term, 15 day Euro ensemble control- comes pretty close to Bermuda. No big signal for any US activity next two weeks on Euro ensembles.


Mid level moisture pushed in by Norbert has reached up to the central Sierra where showers are breaking out this morning. The edge of the deeper moisture registering at the surface is still south and east. Upper level situation is somewhat positive for widespread rains over the Sierra watershed with a jet parked right across California aligned just about with I-80.
JeffMasters has created a new entry.
Quoting VR46L:
I don't get what is so wrong with saying its a fish ... I really dont



Looks like its OTS on the spagetti models




HWRF OTS





GFS says only one that should have concerns is Moi or other Western Europeans ...



Euro OTS


Looking like a fish storm to me but I guess everyone wants a cat5 Threatener


... because it's annoying? Because the possibility of having our first Cape Verde major hurricane since Hurricane Ophelia in 2011 (if the GFS is right, which I doubt it will be) people are proclaiming "Captain Trough saves the US again!" over a storm that's 10-15 days out that hasn't even developed? Personally, I find storms like Earl, Katia, Opehlia, Danielle, all equally as interesting to track.
Quoting Skyepony:
San Diego is up to 58 storm reports now. Most are flooding in Riverside.

There has been a few MESONET reports of more than 1 1/2" of rain in less than an hour this morning. Moisture still streaming up on radar from Norbert's influence..
The reports in western Riverside County appear to be from yesterday. Today's reports are all out in the Thousand Palms/Palm Springs area in east central Riverside County. Riverside County is huge, 7300 square miles, from Orange County in the west to the Arizona border in the east. The eastern area of the county is where the moisture stream is increasing today. It's all desert, with average yearly rainfall less than 10 inches and, as you get further east, less than 4 inches. If they get 2-3 inches in a day, it's a massive flood for them.
sorry Levi but this is important if it verifies......................................
Pedley how is your weather?