Massive African Dust Storm Cooling Atlantic Hurricane Odds for Early August

By: Dr. Jeff Masters , 3:10 PM GMT on July 31, 2013

Share this Blog
85
+

A massive dust storm that formed over the Sahara Desert early this week has now pushed out over the tropical Atlantic, and will sharply reduce the odds of tropical storm formation during the first week of August. The dust is accompanied by a large amount of dry air, which is making the Saharan Air Layer (SAL) much drier than usual this week. June and July are the peak months for dust storms in the Southwest Sahara, and this week's dust storm is a typical one for this time of year. Due in large part to all the dry and dusty air predicted to dominate the tropical Atlantic over the next seven days, none of the reliable computer models is predicting Atlantic tropical cyclone formation during the first week of August.


Figure 1. A massive dust storm moves off the coast of Africa in this MODIS image taken at 1:40 UTC July 30, 2013. Image credit: NASA.


Video 1. The predicted movement through August 3 of this week's Africam dust storm, using the NOAA NGAC aerosol model. Image credit: NOAA Visualization Laboratory.

How dust affects hurricanes
Saharan dust can affect hurricane activity in several ways:

1) 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) from the coast of Africa to the Caribbean, providing hurricanes with less energy to form and grow. Ocean temperatures in the MDR are currently 0.7°F above average, and this anomaly should cool this week as the dust blocks sunlight.

2) The Saharan Air Layer (SAL) is a 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.

3) Dust may also act to produce more clouds, but this effect needs much more study. If the dust particles are of the right size to serve as "condensation nuclei"--centers around which raindrops can form and grow--the dust can act to make more clouds. Thus, dust could potentially aid in the formation and intensification of hurricanes. However, if the dust acts to make more low-level clouds over the tropical Atlantic, this will reduce the amount of sunlight reaching the ocean, cooling the sea surface temperatures and discouraging hurricane formation (Kaufman et al., 2005.)


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.

Dust in Africa's Sahel region and Atlantic hurricane activity
The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18° - 22° N) and the northwestern Sahel (15° - 18° N) (Figure 3.) The dust from the Southwest Sahara stays relatively constant from year to year, but the dust from the Northwest Sahel varies significantly, so 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 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. In 2012 (Figure 3), precipitation across the northwestern Sahel was much above average, which should result in less dust than usual over the Atlantic this fall, increasing the odds of a busy 2013 hurricane season.


Figure 3. Rainfall over the Northwest Sahel region of Africa was about 200% of average during the 2012 rainy season. The heavy rains promoted vigorous vegetation growth in 2013, resulting in less bare ground capable of generating dust. Image credit: NOAA/Climate Prediction Center.

The future of African dust: highly uncertain
A September 2013 paper in the Bulletin of the American Meteorological Society by Joseph Prospero and Olga Mayol-Bracero, "Understanding the Transport and Impact of African Dust on the Caribbean Basin," discusses the large uncertainties on how African dust may change due to climate change. Over the past decade, there has been no clear relationship between African dust and climate indices such as rainfall in the Sahel or the El Niño/La Niña cycle, which "makes it difficult to predict how dust emissions and transport might change over the coming decades as climate changes. The problem is exacerbated by the inability of models (IPCC 2007) to agree on future rainfall trends over large areas of North Africa (including the Sahel) that are known to be major dust sources today and in the recent past."

Links
Saharan Air Layer Analysis from the University of Wisconsin

Atlantic dust forecast from the Tel-Aviv University Weather Research Center

The Saharan Air Layer (SAL) was first described in 1972, in this classic paper: Carlson, T. N., and J. M. Prospero (1972), The Large-Scale Movement of Saharan Air Outbreaks over the Northern Equatorial Atlantic, Journal of Applied Meteorology, 11(2), 283-297

Dr. Amato Evan published a study in Science magazine March 2009 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.

Kaufman, Y. J., I. Koren, L. A. Remer, D. Rosenfeld, and Y. Rudich, 2005a: The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean. Proc. Natl. Acad. Sci. USA, 102, 11 207–11 212.

Wang, Chunzai, Shenfu Dong, Amato T. Evan, Gregory R. Foltz, Sang-Ki Lee, 2012, Multidecadal Covariability of North Atlantic Sea Surface Temperature, African Dust, Sahel Rainfall, and Atlantic Hurricanes, J. Climate, 25, 5404–5415.
doi: http://dx.doi.org/10.1175/JCLI-D-11-00413.1

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: 176 - 126

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 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | 77Blog Index



XD
Member Since: Posts: Comments:
Quoting 171. tornadodude:


Maybe more spouts today
yes that could be..they are warning of possible severe storms tonight..we'll see..sure is hot and humid enough
Member Since: August 6, 2011 Posts: 4 Comments: 42262
Quoting 168. Naga5000:


And the U.S. is a very small landmass in the global scale. Obviously when it's abnormally cold in the U.S. it means the rest of the planet isn't warming...

And we have never seen a Main Blog post about excessive heat records in the US have we?

Couldn't be possible that the topics are handpicked for attention, could it?
Member Since: Posts: Comments:
OK, now that the chances of a hurricane forming in the Atlantic are, say, 25%? So, let's turn our attention to the EPAC till we get some storms in the Atlantic.
Member Since: Posts: Comments:
Get da Ham..

www.solarham.net


IRIS Mission First Light
Last week the Interface Region Imaging Spectrograph (IRIS) mission released its first light imagery. Attached is a fantastic image showing an active region in great detail. The NASA mission will study what is known as the interface region between the photosphere and corona.





Member Since: Posts: Comments:
Quoting 170. LargoFl:
west coast seabreeze if starting to form............


Maybe more spouts today
Member Since: Posts: Comments:
west coast seabreeze if starting to form............
Member Since: August 6, 2011 Posts: 4 Comments: 42262
169. Kumo
Quoting 125. stormchaser19:
Coronal Hole.


That's a good sign that we are still in solar max. Hopefully we'll get some good storms this fall. The second peak of last cycle put on a very good show.

http://spaceweather.com/archive.php?view=1&day=29 &month=10&year=2003
Member Since: Posts: Comments:
Quoting 160. seminolesfan:


I wonder if this will see any mentioning on the main blog with the SAL outbreak and a break in the tropical action? Oh yeah, only hot weather is climate; Cold weather is just weather...


And the U.S. is a very small landmass in the global scale. Obviously when it's abnormally cold in the U.S. it means the rest of the planet isn't warming...
Member Since: Posts: Comments:
Quoting 120. MisterPerfect:
the usual noon poof of xDorian



the trend will be a fierce blob again by tomorrow morning


Probably fiercer, too, he's got tons of energy to tap all to the S of him.
Member Since: Posts: Comments:
Quoting 160. seminolesfan:


I wonder if this will see any mentioning on the main blog with the SAL outbreak and a break in the tropical action? Oh yeah, only hot weather is climate; Cold weather is just weather...


Roger That! Seee post 156... ;)
Member Since: Posts: Comments:
A wandering Jet is what we see changing in the N Hemisphere.



Member Since: Posts: Comments:
Quoting 156. MechEngMet:


Should we start a blog about global cooling now??


NOPE! :P
Member Since: Posts: Comments:
Quoting 121. CybrTeddy:


The conditions in 2002 are totally different from now. A single SAL outbreak doesn't kill a hurricane season. Season so far reminds me of 2010 and 2007 in terms of pre-August conditions.


I wouldnt mind another 2010...that would mean another Igor, another Julia, and another Earl.
Member Since: Posts: Comments:
Quoting 152. TropicalAnalystwx13:

August promises to be cooler to much cooler than average across much of the East USA as well.


I wonder if this will see any mentioning on the main blog with the SAL outbreak and a break in the tropical action? Oh yeah, only hot weather is climate; Cold weather is just weather...
Member Since: Posts: Comments:
In June, note the Warm anomalies in the N Hemisphere, compared to cool ones.

July should be much the same.


Member Since: Posts: Comments:
Most weather stations here on Grand Cayman are showing West, WSW, SW winds.
Member Since: Posts: Comments:
Unmanned Flying Vehicle Detects Hot Tower in Hurricanes

Global Hawk takes High Altitude Imaging Wind and Rain Profiler(HIWRAP) data

Member Since: Posts: Comments:
Quoting 144. seminolesfan:



Lots of cold and minimum-max records this week...


Should we start a blog about global cooling now??
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting 129. stormchaser19:


Couple days ago the SAL was almost nothing, and now seems that the bust season has changed to the Dust season..lol


Because Saharin air outbreaks have never happened in previous seasons.
Member Since: Posts: Comments:
Quoting 135. aquak9:


Dat SHIRT!!


Water Puppy!!! Hi. Haven't seen you all season --yet. Or if you've been posting I must have missed it/them. Welcome, and hello from NOLA west.
Member Since: Posts: Comments:
Quoting 144. seminolesfan:



Lots of cold and minimum-max records this week...

August promises to be cooler to much cooler than average across much of the East USA as well.
Member Since: Posts: Comments:
151. beell
Thanks, Skye, Met, and doggie.
Peace reigns in Wunderland.

Ya'll have a great afternoon.
Member Since: September 11, 2007 Posts: 145 Comments: 16923
no comment
Member Since: Posts: Comments:
Thanks Taco for answering my questions this morning. I appreciate it & hope to see more updates from you in the days to come. Keeping one eye open all the time. Have a great day!
Member Since: Posts: Comments:
This just spells trouble...a tropical storm hitting Vietnam.

Member Since: Posts: Comments:
Quoting 131. Skyepony:

beell was referring to me. Originally his question was directed toward me & I'm a mod..wunderblog moderator (note the green mod next to my handle unless you are in classic). It's not unusual for me to linger in an old blog either. beell knew where I was going to wander back too.


Oh okay, I got ya both now. Thanks for clearing that up. That was specific to you, not a general statement. It all makes sense now.


I thought Beel was trying to be cute/humorous in the previous blog with that 'If you've already jumped...' piece: ...and I just wanted to find out.

That's all. I'll go back in my cell now.

Member Since: Posts: Comments:
146. Skyepony (Mod)
Blowout in Gulf still leaking? Scientists checking for pollution are not allowed within 5 miles of site %u2014 Sheen continues to be observed %u2014 Fire boats remain nearby %u2014 Gas could %u201Cimpact offshore ecosystems%u201D

There isn't alot of timely news about this..


Here's from today in italics..with my thoughts added.

Angelico said no gas is leaking and no sheen has been seen in the water. She said the blowout preventer has not yet been recovered.
yeah we already saw the video..totally false about no sheen or leaking..

The Walter blowout was the second incident in shallow water off Louisiana in less than a month. A crew on a production platform operated by Talos Energy lost control of a well July 9 while trying to plug it. The well leaked small amounts of gas and an oil-water mixture called condensate over three days, but did not suffer a blowout. There was no explosion. There was even less mention of this leaking well. Almost forgot about it.

BSEE had been studying possible changes to blowout preventer requirements before the latest well blowout, Watson said. Those comments have drawn congressional scrutiny. A July 12 letter signed by 11 Republican U.S. House members, including Louisiana%u2019s Steve Scalise, asked Watson about when new rules might be issued and whether they would require drillers to junk current blowout preventers. This is the meat of todays news...They maybe are thinking about doing something about all these faulty blowout preventers.

Quoting 124. MechEngMet:


?? I meant no offense. Who am I underestimating, and how??

No offense taken:P
Member Since: Posts: Comments:
Quoting 143. aquak9:


I withdraw my question, Your Honor!

(sits back down behind table, sighs)


Heya, Aqua. How've you been?
Member Since: Posts: Comments:



Lots of cold and minimum-max records this week...
Member Since: Posts: Comments:
Quoting 139. beell:


No offense meant here either. I took your post to be light-hearted and humorous. But if you saw it...

Anyway, a withdrawal of the question seemed to be in order. :)

That all I meant.


I withdraw my question, Your Honor!

(sits back down behind table, sighs)
Member Since: Posts: Comments:
.
Member Since: Posts: Comments:
Nuttin'

Member Since: Posts: Comments:
The ULL is moving quickly to the West in my opinion,and leaving behind the energy from Ex-Dorian.
Member Since: Posts: Comments:
139. beell
Quoting 124. MechEngMet:


?? I meant no offense. Who am I underestimating, and how??


No offense meant here either. I took your post to be light-hearted and humorous. But if you saw it...

Anyway, a withdrawal of the question seemed to be in order. :)

That all I meant.
Member Since: September 11, 2007 Posts: 145 Comments: 16923
138. VR46L
Quoting 120. MisterPerfect:
the usual noon poof of xDorian



the trend will be a fierce blob again by tomorrow morning


You can set your watch by him ... I think he will become one of those storms that constantly runs around the Globe ...
Member Since: Posts: Comments:
Quoting 116. calkevin77:

Yes. Most of the time it's just remnant moisture but then every now and again a crossover storm rears its head. The 1949 Texas cane for example. That one was a nasty. This is why I've always been curious about the oscillation effect. Obviously we don't have much data in that regards from decades ago but I think given the right conditions, these storms in the pacific can get caught and pulled up inland. So I guess now every year we collect a macro-level view of data the better we can forecast.


Can never link this right. But if you copy and paste it it should take you to the right place. It has some info on how the EPAC storms affect Texas and a lot more.

www.hpc.ncep.noaa.gov/research/txhur.pdf

Texas Hurricane History
David Roth
National Weather Service
Camp Springs, MD
Member Since: Posts: Comments:
You can see the dust!
Member Since: Posts: Comments:
Quoting 120. MisterPerfect:
the usual noon poof of xDorian



the trend will be a fierce blob again by tomorrow morning


Dat SHIRT!!
Member Since: Posts: Comments:
Quoting 43. washingtonian115:
This was a impressive storm..

This was his original forecast


Yep. Moving over that eddy of 80-82° waters of the gulf stream was what did it for Chris to strengthen.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
120. MisterPerfect....I think I see the dust in the dry air layer below Cuba, etc in your Sat pic! Nice shot!
Member Since: Posts: Comments:
131. Skyepony (Mod)
Quoting 127. SouthernIllinois:

That one I ain't gettin' either. At first I thought it read "Never underestimate the Blob".

beell was referring to me. Originally his question was directed toward me & I'm a mod..wunderblog moderator (note the green mod next to my handle unless you are in classic). It's not unusual for me to linger in an old blog either. beell knew where I was going to wander back too.
Member Since: Posts: Comments:
Quoting 120. MisterPerfect:
the usual noon poof of xDorian



the trend will be a fierce blob again by tomorrow morning
In all my years following Tropical Systems more than 25 years,I had never seen anything like this ex-Dorian thing,it looks great this morning,then looks bad this afternoon?,I just want to know what we should expect here in Miami?? for the weekend got some friends coming for a week staying in Miami Beach,I hope we don't get a last minute surprise!!,following this staburn!! systems that don't died easy,they are like a cat having 7 lives,I know nobody is expecting anything,but I will not be relax until all of this move into the Gulf of Mexico,the waters over the Bahamas are very hot!!! and the system is taking it's time to move west.Time will tell!!!.
Member Since: Posts: Comments:
Quoting 121. CybrTeddy:


The conditions in 2002 are totally different from now. A single SAL outbreak doesn't kill a hurricane season. Season so far reminds me of 2010 and 2007 in terms of pre-August conditions.


Couple days ago the SAL was almost nothing, and now seems that the bust season has changed to the Dust season..lol
Member Since: Posts: Comments:
I think our attention should turn to the Caribbean, once the ITCZ over South America moves northward, or wind shear dies down, I give it a week, and the GOM should have something near day 7
Member Since: Posts: Comments:
Cool to see the angle of the sun for these two days

Member Since: Posts: Comments:

Viewing: 176 - 126

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 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 | 76 | 77Blog 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
38 °F
Overcast

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron