Dust forecast for the 2009 Atlantic hurricane season

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

Share this Blog
5
+

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

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: 94 - 44

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 | 35Blog Index

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
328 PM CDT SAT JUN 20 2009

...HOT DRY CONDITIONS TO PERSIST FOR THE NEXT 7 DAYS...

.DISCUSSION...ONE WORD...PERSISTENCE. LATEST SFC ANALYSIS SHOWS
HIGH PRESSURE CENTERED OVER THE LOWER MISSISSIPPI VALLEY PROVIDING
THE FORECAST AREA WITH A LIGHT SRLY LOW-LEVEL FLOW. MEANWHILE
WATER VAPOR IMAGERY SHOWS BLOCKING RIDGE IN PLACE FROM THE SERN
CONUS UP THE PLAINS STATES TO THE CANADIAN PRAIRIES. RESULT IS YET
ANOTHER IN WHAT`S BECOME A LONG LINE OF HOT DRY DAYS OVER THE
REGION WITH JUST SCT HIGH-BASED CU SHOWING UP ON VISIBLE IMAGERY
AND SFC OBSERVATIONS.

NO BIG...IF ANY...CHANGES TO INHERITED FORECASTS. MID/UPPER-LEVEL
RIDGE REMAINS THE PRIMARY PLAYER IN THE REGIONAL WEATHER GAME
THROUGH THE PERIOD. RIDGE AXIS IS PROGGED TO DRIFT WWD WHILE
FLATTENING SOMEWHAT...HOWEVER SUFFICIENT WARM AIR ALOFT IS PROGGED
TO LINGER ENOUGH TO SQUASH ANY CONVECTIVE DEVELOPMENT THROUGH THE
COMING WEEK. AT THE SFC A WEAK FRONTAL BOUNDARY IS SHOWN DRIFTING
SWD INTO THE FORECAST AREA BY MID-WEEK BUT THIS FEATURE CERTAINLY
DOES NOT LOOK STRONG ENOUGH TO OVERCOME THE CAPPING. TEMPERATURES
WILL REMAIN WELL ABOVE NORMAL WITH AFTERNOON MAXES PUSHING THE
CENTURY MARK BY EARLY IN THE WEEK. HEAT INDEX VALUES ARE FORECAST
TO BE IN THE MID 100S...

ETC. ETC. ETC. Sigh. :)
Member Since: Posts: Comments:
Quoting plywoodstatenative:
Gator, how many lives are you willing to put money towards your prediction?


I was being sarcastic. clearly you failed to click the link. I am saying how can we call this season over when it is slow during a slow month its ludicrous.
Member Since: Posts: Comments:


good thing Linfa is not classified as a large cyclone on the JMA scale.
Member Since: Posts: Comments:
Quoting Vortex95:
shear is dominating? no no no it's the tunnels :P.


RitaEvac will tell you its the media doing it...
Member Since: Posts: Comments:
no nothing petrol go on vacation sell your hurricane supplies tell fema to shut down we wont need em as per 23 and any one else that claims the season is over nothing there shear will be high for rest of the year till christmas



Go Keep!
Yeah buddy...LMAO!!!!!

Member Since: Posts: Comments:
Gator, how many lives are you willing to put money towards your prediction?
Member Since: Posts: Comments:
Something is bugging me about this season, its almost like the first two almost tropical systems were a teaser for us. I think the season is building up for a shock come August. My prediction will never be on the amount of storms or their seriousness. However it is on when we could see a ramp up of activity: Gut feeling on this is around the first week of August for a ramp up of activity.
Member Since: Posts: Comments:
c'mon guys its so obvious this season is O-V-E-R over. I mean its June and no development. lol get real, here read this and learn.

(SOUTH FLORIDA JUNE TROPICAL CYCLONE CLIMATOLOGY)

Link
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
no nothing petrol go on vacation sell your hurricane supplies tell fema to shut down we wont need em as per 23 and any one else that claims the season is over nothing there shear will be high for rest of the year till christmas

lol


KOTG , LMAO!
Member Since: Posts: Comments:
Fort Lauderdale / Hollywood Intl Airport
Lat: 26.07 Lon: -80.15 Elev: 8
Last Update on Jun 20, 4:53 pm EDT

Partly Cloudy

90 °F
(32 °C)
Humidity: 62 %
Wind Speed: SE 16 MPH
Barometer: 29.88" (1011.6 mb)
Dewpoint: 75 °F (24 °C)
Heat Index: 101 °F (38 °C)
Visibility: 10.00 mi.
Member Since: Posts: Comments:
Quoting stormpetrol:
I think the Atlantic/Caribbean has at least a 30% chance of a named TS before the end of June.Of course that is just my unprofessional opinion
no nothing petrol go on vacation sell your hurricane supplies tell fema to shut down we wont need em as per 23 and any one else that claims the season is over nothing there shear will be high for rest of the year till christmas

lol
Member Since: July 15, 2006 Posts: 169 Comments: 53296
And (which Im surprised no one has mentioned) But the ITCZ is active for this time of year, we saw near-waves in April that looked like what we would see in August.
Member Since: Posts: Comments:
75 you just never know when one of those models is going to through a cell phone at you... and wake you up to see invest 93, or better yet a ts or hurricane... oh well
(the cell phone comment is about naomi cambell's problems with her help and how she assualts them by throwing cell phones at them)
Member Since: Posts: Comments:
78. Dr3w
Quoting CybrTeddy:


I already did, end of June folks were calling 2008 'average'. Its a bad mistake to underestimate a season. People claim 2006 was a bust, 2006 was exactly average. If Ernesto didn't change track and went into the GOMEX like it was forecasted too as a Category 3 2006 would be remembered as a really bad season.


OR if Chris followed track and didn't get ripped apart.


Or if Alberto became a Category 1 Hurricane.



I remember in 2007 how Andrea and Barry formed before the season started and everybody said it would be a really active year and then when it got quiet for a month and a half how they all labled it a bust until Dean and Felix became cat 5's and every one was on the bandwagon again.

lets just let mother nature run its course and pray for a safe year
Member Since: Posts: Comments:
Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2
Member Since: October 1, 2007 Posts: 81 Comments: 26511
I never remember anyone calling 2008 an average season in June. We all knew that 14-17 was the prediction.
Member Since: Posts: Comments:
post 71.
I always wondered why the models were muddles. Well now I know. Thanks for that.
Member Since: Posts: Comments:
Besides the shear is lessening throughout the Caribbean. You can't call a season 'year of shear' by what you see in Mid June.
I looked back at 2005 posts and blogs, 'Shear rules!' 'year of shear'
Member Since: Posts: Comments:
I think the Atlantic/Caribbean has at least a 30% chance of a named TS before the end of June.Of course that is just my unprofessional opinion
Member Since: Posts: Comments:
Shoot in 2007 people were calling it a bust too.
Infact I remember people calling Dean the next Chris.
Member Since: Posts: Comments:
most models are calling high wind sheer to affect formation for the rest of hurricane season.... and those models would be the Claudia Shiffer, Kate Moss and Naomi Campbell.

Thank you , thank you , thank you very much I'll be here all of June and into early July
Member Since: Posts: Comments:
Quoting IKE:


It's always been this way. Go back to last year on this same date on Dr. Master's blog and I'll guarantee you'll see similar posts.


I already did, end of June folks were calling 2008 'average'. Its a bad mistake to underestimate a season. People claim 2006 was a bust, 2006 was exactly average. If Ernesto didn't change track and went into the GOMEX like it was forecasted too as a Category 3 2006 would be remembered as a really bad season.


OR if Chris followed track and didn't get ripped apart.


Or if Alberto became a Category 1 Hurricane.

Member Since: Posts: Comments:
I'm no scientist, weather expert, but i'm sticking with my earlier prediction of 14/7/4 for 2009.
Member Since: Posts: Comments:
Quoting IKE:


It's always been this way. Go back to last year on this same date on Dr. Master's blog and I'll guarantee you'll see similar posts.


yessir I remember last year as well and the year before and so on... I just wish people would realize this... I'm no rocket scientist and I figured it out...

ok I'm off my soap box and back to chilling
Member Since: Posts: Comments:
Shears !

Member Since: Posts: Comments:
51. Floodman

Hey Flood, nice to see you, how"s things?
Member Since: Posts: Comments:
64. IKE
Quoting SomeRandomTexan:


I know and its a crying shame... from hype to downcasting the roller coaster ride can be very stomach turning...

I remember last month when 90L and all was going on everyone was saying how this was going to be a busy year... sigh..


It's always been this way. Go back to last year on this same date on Dr. Master's blog and I'll guarantee you'll see similar posts.
Member Since: Posts: Comments:
Quoting CybrTeddy:


Mother nature decides it, not shear models.


Exactly!!! my point!
Member Since: Posts: Comments:
62. Dr3w
Quoting KEEPEROFTHEGATE:
iam going to laugh at 23 with that egg on his face come later in the season no one not even 23 knows what will happen how it happens why it happens


good point
Member Since: Posts: Comments:
Quoting Vortex95:
Is really the only limiting factor of storms forming at this moment lets say in the Western Carribean, shear?


yes.
Member Since: Posts: Comments:
Quoting IKE:


And this blog will always be this way.


I know and its a crying shame... from hype to downcasting the roller coaster ride can be very stomach turning...

I remember last month when 90L and all was going on everyone was saying how this was going to be a busy year... sigh..
Member Since: Posts: Comments:
Quoting hurricane23:


Dude i dont need you to explain to me what happens in june and what not.There are plenty of other factors lining up that spell (very slow season).


Mother nature decides it, not shear models. 2008 had dust, shear, so did 2004. 2008 didn't see a single storm in June, only Aurthur that crossed over into June. We've had 1, almost 2 systems before season started even. TD-1 and 90L. To call this season 'very slow' a few days into it, is a bad mistake. People were calling 2006 'very active' during this time.
Shoot 2004 didn't even see its first system till July 31st. And look what happened.
Member Since: Posts: Comments:
57. IKE
Quoting SomeRandomTexan:
if we had a storm form tomorrow then this blog would go from "bust season" to "biggest season on record" it's the nature of the beast


And this blog will always be this way.
Member Since: Posts: Comments:
if we had a storm form tomorrow then this blog would go from "bust season" to "biggest season on record" it's the nature of the beast
Member Since: Posts: Comments:
we may not see anything till mid august but then have one right after another till mid september
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Hey Floodman, how are ya?
Member Since: Posts: Comments:
Wow! some people do get carried away in there predictions... I'm not saying anything except 2 of the main factors are favorable and 1 isn't... when shear relaxes some like it will do then you have a really good chance for a seed to take off... its ashame that we think we know so much when the pros can't even come close to getting it right...
Member Since: Posts: Comments:
Howdy, folks
Member Since: Posts: Comments:
Quoting Vortex95:
I'm begining to wonder if nothing forms by mid July if even 9 storms is generous.


Just because nothing has formed yet does not mean the season is a bust. May I remind you of 2004.
Member Since: Posts: Comments:
to all y'all tomorrow will bring another model that'll have everyone predicting something that unpredictable thus far. Geeesss... I remember 1992.. when there were no storms until......hmmmmmm.... whether there are 3 storms or 23 storms this season it's all about who gets hit, how hard it is & where you are at that time.
Peace.. and stop squabbling all the time y'all
Member Since: Posts: Comments:
The forecast is looking good for a cool-down and wetter period for the state of Florida next week!



QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
427 PM EDT SAT JUN 20 2009

DAYS 2/3...

...FL PENINSULA...

WHILE THEIR HEAVIER AMTS MAY BE OVER-EXAGGERATED DUE TO FEEDBACK
CONTAMINATION...THE NAM/GFS AGREE THAT PERSIST NWLY FLOW BETWEEN
THE AFOREMENTIONED RIDGE OVER THE S CTRL U.S. AND THE LOW OFF OF
THE NORTHEAST COAST WILL DRAW AN ABUNDANCE OF MOISTURE ACROSS THE
PENINSULA...WHERE PWS EXCEEDING 2 INCHES ARE SHOWN AS THIS
MOISTURE POOLS ALONG A BNDRY DROPPING THRU THE STATE. COUPLED
WITH THE WEAK SHRTWV ENERGY EMBEDDED WITHIN THIS FLOW AS
WELL...SPURRING THE DEVELOPMENT OF WEAK SFC WAVES...WHICH WOULD IN
TURN FURTHER ENHANCE THE LOW LVL MOISTURE CONVERGENCE ACROSS THE
REGION...HVY RAINS...PRODUCING AREAL AVGS OF OVER 2 INCHES APPEAR
QUITE PROBABLE AT THIS POINT FOR PORTIONS OF THE SRN PENINSULA ON
DAY 3.

Member Since: Posts: Comments:
iam going to laugh at 23 with that egg on his face come later in the season no one not even 23 knows what will happen how it happens why it happens
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Shear, shear and more shear. Correlates well with the CFS:
Member Since: Posts: Comments:

Viewing: 94 - 44

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 | 35Blog 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

Scattered Clouds
78 °F
Scattered Clouds