Dust forecast for the 2009 Atlantic hurricane season

By: Dr. Jeff Masters , 6:58 PM GMT on June 20, 2009

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There will be less African dust than usual over the tropical Atlantic during this year's hurricane season, according to a new experimental dust forecast issued by Dr. Amato Evan of the University of Wisconsin. Dr. Evan used a statistical model that correlated levels of dust activity in past years with rainfall over the Sahel region of Africa and a natural regional wind pattern known as the North Atlantic Oscillation (NAO). He forecasts that dust levels over the Main Development Region (MDR, 8 - 20°N & 15 - 65°W) for Atlantic hurricanes during this year's hurricane season will be similar to last year's below-average levels, thanks in large part to plentiful rains over the Sahel region of Africa during the 2008 rainy season (Figure 1). However, the dust levels expected this year do not approach the record lows seen in 1994 and 2005. Dust forecasts made in May or June are skillful going out five months, with a skill 11 - 16% better than a "no-skill" forecast using climatology.


Figure 1. Rainfall over the Sahel region of Africa was generally 50 - 100 mm (2 - 4 inches) above average during the 2008 rainy season (about 20 - 80% above average). The heavy rains promoted vigorous vegetation growth in 2009, resulting in less bare ground capable of generating dust. Image credit: NOAA/Climate Prediction Center.

The Sahara and the Sahel: significant sources of dust
The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18° - 22° N) and the northwestern Sahel (15° - 18° N) (Figure 2). The dust that originates in the Southwest Sahara stays relatively constant from year to year. However, the dust from the northwestern Sahel varies significantly from year to year, and understanding this variation may be a key factor in improving our forecasts of seasonal hurricane activity in the Atlantic. The amount of dust that gets transported over the Atlantic depends on a mix of three main factors: the large scale and local scale weather patterns (windy weather transports more dust), how wet the current rainy season is (wet weather will wash out dust before it gets transported over the Atlantic), and how dry and drought-damaged the soil is. The level of drought experienced in the northwestern Sahel during the previous year's rainy season (June - October) is the key factor of the three in determining how much dust gets transported over the Atlantic during hurricane season, according to a January 2004 study published in Geophysical Research Letters published by C. Moulin and I. Chiapello. A dry rainy season the previous year will make an expanded area of loose soil which can create dust. It is also possible that the corresponding changes in vegetation can alter the regional weather patterns, causing more dust production.


Figure 2. Map of the mean summer dust optical thickness derived from satellite measurements between 1979 and 2000. Maximum dust amounts originate in the northern Sahel (15° to 18° N) and the Sahara (18° to 22° N). The Bodele depression in Chad is also an active dust source. Image credit: Evidence of the control of summer atmospheric transport of African dust over the Atlantic by Sahel sources from TOMS satellites (1979-2000) by C. Moulin and I. Chiapello, published in January 2004 in Geophysical Research Letters.

How dust suppresses hurricanes
Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) off the coast of Africa, providing hurricanes with less energy to form and grow. Dust also affects the Saharan Air Layer (SAL), an layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane. The dust may also act to interfere with the formation of cloud drops and rain drops that these thunderstorms need to grow, but little is known about such effects. It is possible that dust may act to help hurricanes by serving as "condensation nuclei"--centers around which raindrops can form and grow.

For additional reading
Dr. Evan published a study in Science magazine this March showing that 69% of the increase in Atlantic sea surface temperatures over the past 26 years could be attributed to decreases in the amount of dust in the atmosphere.

Jeff Masters

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1044. Levi32
Quoting hurricane2009:
Levi is the heat content the ability of a body of water to hold its temperature?


As I understand it it's primarily based on the depth of the warm water. If you compare the TCHP map with the 26c isotherm-depth map, you can see they usually match up pretty well.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
True Vort, its a wait and see situation.
We'll have to see if the 8 PM TWO mentions it. Then we'll have 2 area's of interest.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
Quoting Levi32:


Well....only higher in the loop current. The gulf has really been cooking since that high moved in though. The heat content is moving upwards rapidly.

Yep, but it is still unusual. I also noticed the warmer area near the TX coast, that is already above 60 on the TCHP map.

This just makes me hope that much more for a season like 2006, where nearly everything recurves way out in the Atlantic. If anything gets into the GOM, its off to the races... and there isn't a "good" place for a storm to go, once it is in the Gulf. Anywhere it turns, its going to spread some destruction.
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Quoting presslord:
Ha! It's too dadgummed hot here in the Carolinas to breath in and out...

And which Carolina are you talking about?!
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1039. Levi32
Quoting jeffs713:
How wierd is it that the GOM was higher TCHP than the EPac?


Well....only higher in the loop current. In general the EPAC still has bigger areas of higher TCHP. The gulf has really been cooking since that high moved in though. The heat content is moving upwards rapidly.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
1038. K8eCane
Quoting CybrTeddy:
Don't quote K8, flag, report, ignore, repeat.


Cyber
that works both ways ya know
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Quoting Levi32:
Andres is not in an area of particularly high ocean heat content. The warm water is fairly shallow where Andres' center is right now. I'm thinking that due to this, proximity to Mexico, and less than perfect upper-level conditions, Andres will not be able to intensify to more than a Cat 1 hurricane.

How wierd is it that the GOM was higher TCHP than the EPac?
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1036. vortfix
MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
300 PM EDT MON JUN 22 2009

MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA
AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W.

SW N ATLC...
VERY LITTLE CHANGE IN REASONING FROM THE PREVIOUS DISCUSSION
BASED ON THE LATEST MODEL GUIDANCE. THE MAIN FCST ISSUE REMAINS
THE EVOLUTION OF THE EXPECTED SWATH OF STRONG SLY WINDS OVER THE
FAR NE PORTIONS OF THE ZONE FOR TUE INTO WED. ALL MODELS LATCH
UNTO A STRONG VORT MAX CURRENTLY OVER THE EASTERN MID ATLC
STATES WHICH IS FCST TO DIVE SWD ON THE W SIDE OF THE
ANOMALOUSLY DEEP TROUGH JUST OFF THE E COAST. A SFC LOW IS
EXPECTED TO DEVELOP OVERNIGHT TONIGHT ALONG AN EXISTING COLD
FRONT OVER THE N CENTRAL PORTION OF THE ZONE AND MOVES ACROSS
31N BETWEEN 68W AND 70W...DEPENDING ON THE MODEL OF CHOICE.
THERE IS CONTINUED CONFIDENCE THAT THERE WILL NOT BE SUSTAINED
GALE FORCE WINDS OVER FORECAST WATERS IN THE ZONE ON TUE GIVEN
THE OUTPUT FROM THE 12Z MODELS. THE 12Z GFS BRIEFLY SHOWS WINDS
TO 35 KT ON THE EASTERN SIDE OF THE DEVELOPING SURFACE LOW
OVERNIGHT...BUT THERE IS LITTLE SUPPORT FROM THE ENSEMBLES WITH
THE SREF CURRENTLY SHOWING LESS THAN A 5 PERCENT CHANCE OF
GALES. IN ADDITION...THE 12Z GFS GENERATES OVER 5.50 INCHES OF
RAIN WITH THE DEVELOPING LOW AROUND THE SAME TIME...A LIKELY
SIGN OF GRID-SCALE FEEDBACK. THUS WILL FCST 20-30 KT WINDS WITH
HIGHER GUSTS THIS PACKAGE. IN ADDITION...THE MODELS DEVELOP
ANOTHER WAVE DEVELOPING FURTHER S ALONG THE TROUGH ON WED WITH A
ANOTHER SURGE OF WINDS. DETAILS OF THE ULTIMATE EVOLUTION OF THE
WIND FIELD ARE HIGHLY RELIANT UPON THE SPEED...INTENSITY...AND
TRACK OF THE SHORTWAVE ENERGY DROPPING SOUTH ALONG THE BACKSIDE
OF THIS AMPLIFIED TROUGH THROUGH THE EASTERN U.S...SOMETHING THE
MODELS RARELY HANDLE WELL...BUT THE CURRENT TREND WOULD SUPPORT
A BROADENED TROUGH WITH MOVING MULTIPLE SHORTWAVE SYSTEMS
PASSING QUICKLY THROUGH THE BASE OF THE TROUGH...MAKING ANY
SIGNIFICANT SURFACE DEVELOPMENT LESS LIKELY...AND HENCE ANY
SUSTAINED GALE FORCE WINDS.



This is what I said earlier.
It is extremely difficult to know for sure what might evolve in baroclinic situations.

Have a nice day all.


Member Since: October 29, 2007 Posts: 135 Comments: 46068
1035. Levi32
Quoting jcpoulard:
Make a look between 50W-60W and 8N to 15N.
Would like to know if it's a Tropical Wave or and area of sparse thunderstorm.

Did this thing need to be watch for further development, or if is just nothing.

Appreciate if some specialist could give me some idea.... because here in Haiti every rain maker give us troubles by tons.

Thanks.


Yes it is a tropical wave. Right now it's not a threat because there is extremely strong shear across the entire Caribbean due to the TUTT. In 4-5 days it may need to be watched in the western Caribbean as shear lessens under a building upper high, but until then it's not an issue.

As for rainfall it looks like the wave will pass far enough south not to cause problems for you in Hispaniola.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
1034. NEwxguy
Afternoon,all,not much going on out there,except for our nor'easter up here making our weather dismal,dismal,dismal.
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Make a look between 50W-60W and 8N to 15N.
Would like to know if it's a Tropical Wave or and area of sparse thunderstorm.

Did this thing need to be watch for further development, or if is just nothing.

Appreciate if some specialist could give me some idea.... because here in Haiti every rain maker give us troubles by tons.

Thanks.
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Don't quote K8, flag, report, ignore, repeat.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
Quoting K8eCane:



and what you said sounded like an ignorant "ninny ninny boo boo" I hear that crap too much on here
its ignorant
nobody but YOU said anything at all about a low off the carolinas
THAT WASNT ME, BUT NICE COMMENT ANYWAY. Now try to send it to the right person.
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1030. vortfix
MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
300 PM EDT MON JUN 22 2009


GULF OF MEXICO...
LOW PRES TROUGH IN THE SW GULF IN BRINGING SE FLOW ABOVE 20 KT
ON ITS EASTERN SIDE...WITH WINDS AND SEAS HIGHER WITHIN THE
SCATTERED TSTMS W OF 93W S OF 24N. THE TROUGH WILL DISSIPATE ON
WED AS IT DRIFTS W.
SURFACE HIGH PRES OVER THE N CENTRAL GULF
WILL DRIFT WESTWARD THROUGH THE WEEK. AS THE HIGH DRIFTS
WEST...WINDS WILL BECOME NW AT 15 TO 20 KT TUE AND WED IN
RESPONSE TO THE DEEPENING LAYER LOW IN THE WESTERN N ATLC. RIDGE
BUILDS WWD OVER THE GULF ALONG 25N THU AND FRI.
Member Since: October 29, 2007 Posts: 135 Comments: 46068
Ok, children, to your corners until you can behave and get along! :)
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1027. boyzNme
Quoting 69Viking:


98 with a heat index of 108 down here along the coast! So much for the GOM waters keep us cooler than places inland!


95 & with 113 heat index - 3 miles from the atlantic in Boca. I had to come in from painting - you just can't even breath out there.
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1026. Ossqss
It is a new moon today, that explains everything. A new Moon and heat index over 100 does not mix well, obviously !

Link
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Stormjunkie is spending the week out at Folly Beach with his family...

He makes me sick...
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1024. Levi32
Andres is not in an area of particularly high ocean heat content. The warm water is fairly shallow where Andres' center is right now. I'm thinking that due to this, proximity to Mexico, and less than perfect upper-level conditions, Andres will not be able to intensify to more than a Cat 1 hurricane.

Member Since: November 24, 2005 Posts: 635 Comments: 26547
1023. gator23
Good Afternoon all!
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1022. fire635
Quoting 69Viking:


I can't remember it being this hot in June! Thankfully the A/C at the job is working great!


Wow.... if the Jacksonville temp on your link is right, than thats some major heat. Florida at 104.5 Thats hot!

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1021. KEEPEROFTHEGATE (Mod)
better cool down soon heat going to a few heads
Member Since: July 15, 2006 Posts: 169 Comments: 53296
1018. Levi32
Andres is already attempting to start the process of forming an eye. Convective banding is wrapping tight around the center which you can see in visible imagery.
Member Since: November 24, 2005 Posts: 635 Comments: 26547
I've been on weather underground since 2001. way before the blog. I've used diffrent email accounts and screenames.
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Laungage is being used! Flag, ignore, repeat.
When using Dr. Masters' blog, please refrain from posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself. Please do not engage in personal attacks or bickering. Material not conforming to these standards should be flagged with the button and ignored.
Rules of the Road — How to ignore a blogger

During active periods of hurricane season, these rules will be strictly enforced. Violations will be met with a minimum 24 hour ban.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
1014. Ossqss
Quoting presslord:
Ha! It's too dadgummed hot here in the Carolinas to breath in and out...


Where is that place ?
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LOL! I feel you Press, look at Ike he's in the triple digets! Nice day to work on that ladies tan.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
Anyways, off that.
The BOC Blob 'Possible-93L' regarding it, we will have to wait to the QuickSAT (can't wait till they launch one off on a Delta IV in a few years, just in time for the 2013 Atlantic Hurricane season)
Member Since: July 8, 2005 Posts: 259 Comments: 23564
Uhh...my 8 Ball does not agree with that!
ROFL

See you kiddies later...I'm more concerned with the severe potential this afternoon regarding Central/South Florida.

Y'all can visit my blog for all the developments on that.



What severe weather potential in florida are you referring to? From what i have seen, the whole state is gonna be bone dry today with very few if any storms. The forecast for severe storms was way overexagerated.
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Ha! It's too dadgummed hot here in the Carolinas to breath in and out...
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Quoting RMM34667:
I know it is HOT. But it can't be that hot??

Sea Ranch, Hudson, Florida (PWS)
Updated: 2 sec ago
95.1 F
Clear
Humidity: 100%
Dew Point: 95 F
Wind: 4.0 mphfrom the NNW
Wind Gust: 11.0 mph
Pressure: 19.99 in (Falling)
Heat Index: 162 F
Visibility: 10.0 miles
UV: 15 out of 16
Clouds: Clear -
(Above Ground Level)
Elevation: 6 ft



And thats a PWS station... cant have dewpoint in the 90s. They need to remove all PWS stations installed and get new ones because they all suck across the country from what Im seeing
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But you didn't start blogging to like, 2007-08ish because I remember you from last year only. And funny thing is, the blog's weren't created till '05. Lol.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
1004. Levi32
Quoting hurricane2009:
A little tidbit for you folks, if you look at the Western Atlantic Visible, you can see both Andres and the area in the BOC, if you zoom in between the two areas you can get a nice closeup of both, that way you dont have to use 2 separate tabs to watch them both


Like this
Member Since: November 24, 2005 Posts: 635 Comments: 26547
Someones a little hostile this afternoon...
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1002. beell
Hello, folks,
Please send the BOC thing to the BOTX.

Pretty stong pressure gradient setting up in the W ATL.

850mb
12Z GFS
Valid Tue, 18Z

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1001. K8eCane
Hi Press!

Ahhh...since i've only been on here since about 2004. maybe i shouldnt say hi
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Quoting presslord:


Gggggrrrrrr!!!!!


Uhoh! Press breath in and out LOL.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
I know it is HOT. But it can't be that hot??

Sea Ranch, Hudson, Florida (PWS)
Updated: 2 sec ago
95.1 °F
Clear
Humidity: 100%
Dew Point: 95 °F
Wind: 4.0 mphfrom the NNW
Wind Gust: 11.0 mph
Pressure: 19.99 in (Falling)
Heat Index: 162 °F
Visibility: 10.0 miles
UV: 15 out of 16
Clouds: Clear -
(Above Ground Level)
Elevation: 6 ft

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Quoting K8eCane:



and what you said sounded like an ignorant "ninny ninny boo boo" I hear that crap too much on here
its ignorant
nobody but YOU said anything at all about a low off the carolinas


Gggggrrrrrr!!!!!
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Quoting K8eCane:



here we go wit the IDIOTS trying to make a war out of this


Really? Last time I checked I've been on this blog longer than you and I've never been called such. I personally think Both blobs have chance of development. I was only ridiculing his choice of words about Levi's comments, both have a good cance of development in my opinion. But the Bahama's blob has high wind shear over it and is a cold core system. It needs to be persistant.
Member Since: July 8, 2005 Posts: 259 Comments: 23564
And my crystal ball says all your crystal balls are suffering from convective feedback lol


Uhh...my 8 Ball does not agree with that!
ROFL

See you kiddies later...I'm more concerned with the severe potential this afternoon regarding Central/South Florida.

Y'all can visit my blog for all the developments on that.

Member Since: October 29, 2007 Posts: 135 Comments: 46068
Quoting vortfix:
Baroclinic low pressure centers are extremely difficult to classify either way "before" they actually develop Levi.
None of the models are even close to accurate in that regard.

After all my years dealing with the tropics I have found that possible baroclinic features need to be monitored closely as it is never a sure bet either way.

That BOC Blob should be history by 36 hours from what I see.





See?!?!?!?!?! Straight forward, easy to follow, uses common English words in a simple enough fashion that even I can follow it....

That's what I'm talkin' 'bout!!!!!!!!!!
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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.