Four invests in the Atlantic; fair weather in Arctic to drive rapid sea ice loss

By: Dr. Jeff Masters , 3:38 PM GMT on August 12, 2011

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It's a busy day in the tropical Atlantic, with the National Hurricane Center tracking four areas of interest (Invests.) None of these systems is a danger to any land areas over the next three days. The disturbance of most concern is the one farthest from land, a tropical wave that emerged from the coast of Africa two days ago. This wave, (Invest 93L), is located about 500 miles southwest of the Cape Verde Islands, and is moving westward at 15 - 20 mph. Recent visible satellite loops show that 93L has lost some of its heavy thunderstorms since yesterday, and the system is poorly organized, though there is a good deal of spin to the system. There is dry air to its north that is interfering with development. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing high wind shear in excess 20 knots affecting 93L, which has undoubtedly contributed to the storm's loss of organization. Sea surface temperatures are 27.5°C, which is one degree above the 26.5°C threshold usually needed to support a tropical storm.


Figure 1. Morning satellite photo of the four Invests in the Atlantic today.

Forecast for 93L
High wind shear above 20 knots is predicted along 93L's path through Saturday afternoon, followed by a drop to the moderate range, 10 - 20 knots, for the succeeding four days. This should allow the storm to organize over the weekend. 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 40% chance of developing into a tropical depression by Sunday morning in their 8am outlook. Given 93L's recent struggles, I'd put these odds at 30%.

92L
An African wave midway between the northern Lesser Antilles Islands and the coast of Africa, near 18°N 45°W, is moving west-northwest at 20 mph. This system, (Invest 92L), is being given a 40% chance of development by NHC. Recent visible satellite loops show a modest amount of heavy thunderstorm activity, but no signs of a surface circulation. A Windsat pass from 8:04 am EDT this morning also showed no surface circulation, and noted top winds of around 35 mph. Water vapor satellite loops show that a large area of dry air surrounds 92L, and this dry air is causing problems for the storm. The SHIPS model and University of Wisconsin CIMSS wind shear analysis are showing moderate wind shear of 10 - 20 knots affecting 92L. Sea surface temperatures are 27 - 27.5°C, which is a degree above the 26.5°C threshold usually needed to support a tropical storm.

Forecast for 92L
Moderate wind shear of 10 - 20 knots is predicted along 92L's path over the coming five days, which should allow the storm to organize if it can handle the dry air surrounding it. 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 40% chance of developing into a tropical depression by Sunday morning in their 8am outlook. A steady west-northwest motion for 92L is predicted by all of the models, which should make the storm miss the Lesser Antilles by a comfortable margin. However, Bermuda may be at risk from 92L next week.

94L
A broad low pressure system about 700 miles northeast of the northern Lesser Antilles Islands has developed a small amount of heavy thunderstorm activity, and may be a threat to become a tropical depression early next week. This system, (Invest 94L), is currently headed west-southwest at 10 mph, but is expected to turn northwest later today. Recent visible satellite loops show some spin to the cloud pattern at middle levels of the atmosphere, but no signs of a surface circulation. This system is also battling dry air, which is keeping the its heavy thunderstorms relatively meager. The SHIPS model is showing moderate wind shear of 10 - 20 knots affecting 94L. Sea surface temperatures are 28°C.

Forecast for 94L
Moderate wind shear of 10 - 20 knots is predicted along 94L's path over the coming five days, which should allow slow development, if it can handle the dry air surrounding it. None of our reliable models for predicting tropical storm formation (GFS, ECMWF, NOGAPS, and UKMET) show no development of 94L, and NHC gave 94L just a 20% chance of developing into a tropical depression by Sunday morning in their 8am outlook. Bermuda is the only land area that needs to be concerned with 94L.

95L
The final invest out there is an area of disturbed weather along on old frontal boundary several hundred miles off the coast of North Carolina. This sytem, Invest 95L, is headed northeastwards out to sea, and is not a threat to any land areas.



Figure 2. Arctic sea ice extent on August 11, 2011, was the 2nd lowest on record for the date. The Northeast Passage and Northwest Passage (southern route) were both ice-free. Image credit: UIUC Cryosphere Today.

Arctic sea ice poised to undergo record decline in mid-August
A strong high pressure system with a central pressure of 1035 mb has developed over the Arctic north of Alaska, and will bring clear skies and warm southerly winds to northeast Siberia and the Arctic during the coming week, accelerating Arctic sea ice loss. Widespread areas of northeastern Siberia are expected to see air temperatures 4 - 12°C (7 - 22°F) above average during the coming week, and the clockwise flow of air around the high pressure system centered north of Alaska will pump this warm air into the Arctic. Arctic sea ice extent, currently slightly higher than the record low values set in 2007, should fall to to its lowest extent for the date by the third week of August as the clear skies and warm southerly winds melt ice and push it away from the coast of Siberia. This weather pattern, known as the Arctic Dipole, was also responsible for the record sea ice loss in 2007, but was stronger that year. The weather conditions that led to the 2007 record were quite extreme--one 2008 study led by Jennifer Kay of the National Center for Atmospheric Research showed that 2007's combination of high pressure and sunny skies in the Arctic occur, on average, only once every 10 - 20 years. The 2011 summer weather pattern in the Arctic has not been nearly as extreme as in 2007, but the total sea ice volume has declined significantly since 2007, leading to much loss of old, thick, multi-year ice, making it easier to set a new low extent record with less extreme weather conditions. The GFS model is predicting that the Arctic Dipole will weaken by 8 - 15 days from now, with cloudier weather and weaker high pressure over the Arctic. This should slow down the rate of Arctic sea ice loss to very near the record low values observed in 2007. It remains to be seen if 2011 Arctic sea ice extent will surpass the all-time low set in September 2007; it will be close, and will depend on the weather conditions of late August and early September, which are not predictable at this time. It is already possible to sail completely around the North Pole in ice-free waters through the Northeast Passage and Northwest Passage, according to sea ice maps maintained by the UIUC Cryosphere Today website. This marks the fourth consecutive year--and the fourth time in recorded history--both of these Arctic shipping routes have melted free. Mariners have been attempting to sail these passages since 1497. This year, the Northeast Passage along the north coast of Russia melted free several weeks earlier than its previous record early opening.

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Jeff Masters

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Quoting TORMENTOSO83:
Anyone thinks this could be a fishstorm season? Just a question!!!


It is a little too late for that - that ended when Arlene made landfall in Mexico.
Member Since: July 6, 2010 Posts: 113 Comments: 31430
Quoting presslord:


their's no excuse for this....you'rejust being mean
Just seizing the moment... nothing bad intended....
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Quoting TomTaylor:
Remnants of Emily/94L are in an interesting location at the moment. 94L is smushed right in between the high over Bermuda and the one over the Azores region. This is producing southeasterly to southerly winds on the east side of the storm and northeasterly or even northerly winds on the west side of the system, naturally favoring an inverted trough or cyclonic vorticity in the area.



Convection is decent and fairly consolidated over 94L, but it is not very intense. Shear is low at the moment and there's also a lot of moisture. Unfortunately for 94L, upper level winds be fairly strong around the deep layer high over Bermuda. This will prevent it from getting any ULAC aloft and is keeping upper divergence low.

Where it will go and whether or not it will develop still remain fairly uncertain. GFS has been consistently splitting the moisture field sending one piece out to the north around the Azores high and another piece around the Bermuda high (or Azores/Bermuda high since by that time they bridge together). So it will be interesting to see where the storm goes and whether or not it will develop.


To add on to this, the NAM has been consistently developing 94L after it is split in two by the two ridges joining together. I know the NAM is not the most reliable model and it definitely has trouble over the tropics. However, since the NAM has a higher resolution than the global models and has had a pretty good handle on a few of our other small systems so far, we can't rule out the possibility it is showing.

To show what I mean by consistency, here's a loop of the last four runs for August 15th at 12 UTC.




So that makes the last 4 runs in a row from the NAM now showing potential development from part of 94L.


Anyway, just something to keep in mind, not saying it will actually come to fruition.
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Quoting gulfbreeze:
Why is the Blog so Slow?


Maybe it has something to do with the moon.
Member Since: July 6, 2010 Posts: 113 Comments: 31430
Why is the Blog so Slow?
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Levi,do you see the CV season that is upon us having systems classified in the MDR west of 40W instead of having formations In the Eastern Atlantic near the CV islands because of the persistant monsoon trough?
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Levi, how active do you foresee the rest of August being?

Member Since: July 6, 2010 Posts: 113 Comments: 31430
1001. Levi32
Quoting Hurricanes12:
Levi, why are conditions in the Central Pacific generally hostile for tropical cyclones to form?


Mostly because of cold water, from a combination of the equatorial current coming from the east, and the California current coming from the northeast, both cold currents limiting 26C water to a thin sliver, especially in La Nina years.

The ITCZ is also not as active in the central Pacific. In fact, the central Pacific is often the place where the ITCZ is least active around the entire Earth. There is no monsoonal flow to aid development like in the western or eastern Pacific.

Here is a picture of the current SSTs, showing how cool the water is overall, with only a thin region of 28C temperatures.

Member Since: November 24, 2005 Posts: 635 Comments: 26547
Quoting KEEPEROFTHEGATE:
not long just taking a little nap you know those sleepers some can be heavy
LMAO!
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.
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Quoting stormpetrol:
Gotta a feelin 93L will be bloomin tomorrow!
I think so too.
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Storms of the day: TD 6
94L
Member Since: September 2, 2006 Posts: 110 Comments: 6874
Here in the N W Florida Panhandle Sept. & the First half of Oct. has always been our main season. If the high over Texas breaks down at the end of August look out!The season so far has just been a warm up for the real season to come!!!
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Quoting stormpetrol:
Gotta a feelin 93L will be bloomin tomorrow!


I agree. Wind shear will be dropping tomorrow.
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Quoting EYEStoSEA:


The "big picture".
Member Since: July 6, 2010 Posts: 113 Comments: 31430
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Will someone please post a graphic showing the ridge 93L will be humping?
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Gotta a feelin 93L will be bloomin tomorrow!
Member Since: April 29, 2007 Posts: 0 Comments: 7663
With so many active systems, full of heat, tracking north. Will this accelerate the melting of the Polar ice.
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Quoting Neapolitan:


Winds are down, pressure is up.


Yeah. Not looking good for 92L with SAL affecting the storm and wind shear expected to increase as we head into tomorrow.

Still hope for 93L and 94L.
Member Since: July 6, 2010 Posts: 113 Comments: 31430
Quoting TropicalAnalystwx13:
AL, 92, 2011081300, , BEST, 0, 191N, 487W, 25, 1013, DB, 34, NEQ, 0, 0, 0, 0, 1014, 150, 70, 0, 0, L, 0, , 0, 0, INVEST, M,


Winds are down, pressure is up.
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Invest 92L has weakened.

AL, 92, 2011081300, , BEST, 0, 191N, 487W, 25, 1013, DB, 34, NEQ, 0, 0, 0, 0, 1014, 150, 70, 0, 0, L, 0, , 0, 0, INVEST, M,
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Quoting WeatherNerdPR:

Lucky!
Well we get out late as well. So I guess it just depends on when you want to be in school.
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Levi, why are conditions in the Central Pacific generally hostile for tropical cyclones to form?
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Quoting trHUrrIXC5MMX:
Wouldn't the new Pacific Invest be a big thing to deal with for Hawaii later on...?



With that hell of a high pressure system blocking it and the colder SSTs near Hawaii, I don't think so.
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ATCF's 0000Z update for TD6:

AL, 06, 2011081300, , BEST, 0, 361N, 623W, 30, 1011, TD, 34, NEQ, 0, 0, 0, 0, 1014, 175, 30, 0, 0, L, 0, , 0, 0, SIX, M,
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Quoting trHUrrIXC5MMX:
Wouldn't the new Pacific Invest be a big thing to deal with for Hawaii later on...?




I haven't looked at it, but SSTs are below 26C most of the way to Hawaii, which is near 20N, 160W, not quite visible on this image.

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Quoting TomTaylor:
Dang forgot people were already starting school

I don't start again until a little ways into September

Lucky!
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Wouldn't the new Pacific Invest be a big thing to deal with for Hawaii later on...?


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977. ackee
THERE is a lot dry air near the windward ISLAND if 93L does not start bulid some conevnction soon the system may not devlop until it reach the westrn carrb gueess we see
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976. Relix
93L needs to gain strength soon or it will go into the Caribbean.
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975. ackee
I wonder how much storm we will have in AUG
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Quoting uptxcoast:
Houston hit 101 degrees today, extending its 100-degree-day streak to 12. Longest ever is 14 days, set in 1980. Records go back to 1895.

Hopefully the streak will end here as tomorrow it is forecast to be 99 degrees and a 20% chance of rain. That equals to an 80% chance of foul language.
Austins near 30 straight, their old record was 21, lots of clouds and 103 today. I am hearing the High Pressure may move out by end of August? Some computer models are giving hope. Lots of tropical activity coming up hopefully Texas gets a shot at rain by September. Was only 101 at my house today, one of coolest days in the last 60. Levi said a model is showing high pressure maybe out of Texas by September I believe? This could open up gulf and allow storms to move this way?
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ATCF's 0000Z 94L update:

AL, 94, 2011081300, , BEST, 0, 257N, 571W, 25, 1013, DB, 34, NEQ, 0, 0, 0, 0, 1015, 175, 70, 0, 0, L, 0, , 0, 0, INVEST, M,
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Just for old time sakes...Karl, Igor and Julia :)


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Fresh ASCAT pass of the west side of 93L shows very light winds in the region, bordered by ENE winds to the north and SW winds to the south, indicating that 93L is still embedded within the monsoon trough.

Member Since: November 24, 2005 Posts: 635 Comments: 26547
Quoting WeatherNerdPR:
This day is not normal...wish I hadn't gone to school today. LOL
Dang forgot people were already starting school

I don't start again until a little ways into September
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Quoting Levi32:
MIMIC-TPW imagery from CIMSS depicts nicely how 92L is getting blasted by dry Saharan air, and 93L is still doing pretty well, under the protection of the monsoon trough, despite the lack of convection.



And it has shear to contend with tomorrow.
Member Since: July 6, 2010 Posts: 113 Comments: 31430
MIMIC-TPW imagery from CIMSS depicts nicely how 92L is getting blasted by dry Saharan air, and 93L is still doing pretty well, under the protection of the monsoon trough, despite the lack of convection.

Member Since: November 24, 2005 Posts: 635 Comments: 26547
Remnants of Emily/94L are in an interesting location at the moment. 94L is smushed right in between the high over Bermuda and the one over the Azores region. This is producing southeasterly to southerly winds on the east side of the storm and northeasterly or even northerly winds on the west side of the system, naturally favoring an inverted trough or cyclonic vorticity in the area.



Convection is decent and fairly consolidated over 94L, but it is not very intense. Shear is low at the moment and there's also a lot of moisture. Unfortunately for 94L, upper level winds be fairly strong around the deep layer high over Bermuda. This will prevent it from getting any ULAC aloft and is keeping upper divergence low.

Where it will go and whether or not it will develop still remain fairly uncertain. GFS has been consistently splitting the moisture field sending one piece out to the north around the Azores high and another piece around the Bermuda high (or Azores/Bermuda high since by that time they bridge together). So it will be interesting to see where the storm goes and whether or not it will develop.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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