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: 894 - 844

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

894. futuremet
4:34 PM GMT on June 22, 2009
Quoting hurricane2009:
vorticity is actually better over mainland Mexico than the BOC, that should tell you something right there



That was 200MB vorticity
Member Since: July 19, 2008 Posts: 43 Comments: 4051
893. Orcasystems
4:34 PM GMT on June 22, 2009
Member Since: October 1, 2007 Posts: 81 Comments: 26493
892. reedzone
4:33 PM GMT on June 22, 2009
Wasn't looking at that one.. I was looking at this one.
http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8vor4.html
Member Since: July 1, 2008 Posts: 13 Comments: 7334
891. vortfix
4:33 PM GMT on June 22, 2009
Here we go all you Florida peeps!



Photobucket


MESOSCALE DISCUSSION 1272
NWS STORM PREDICTION CENTER NORMAN OK
1125 AM CDT MON JUN 22 2009

AREAS AFFECTED...CNTRL AND SRN FL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 221625Z - 221830Z

SCATTERED THUNDERSTORMS ARE EXPECTED TO FORM ALONG THE E FL COAST
LATER THIS AFTERNOON WITH A THREAT OF DAMAGING WIND GUSTS. SOME HAIL
MAY OCCUR AS WELL.

MORNING SOUNDINGS SHOWED A VERY MOIST AND UNSTABLE AIR MASS ACROSS
FL WITH MID TO UPPER 70S F DEWPOINTS IN THE BOUNDARY LAYER. AT THE
SAME TIME...SOME RELATIVELY DRY AIR WAS IN PLACE IN THE MID LEVELS.
THIS CAN ALSO BE SEEN ON THE WATER VAPOR IMAGERY. THIS LAYER OF DRY
AIR IS EXPECTED TO HAMPER DEVELOPMENT UNTIL LATE AFTERNOON...WHEN
BOTH MAX HEATING IS ACHIEVED AND A MID LEVEL MOIST PLUME ARRIVES OUT
OF THE N...HELPING TO CONDITION THE ENVIRONMENT. GIVEN NWLY SFC
WINDS ACROSS THE PENINSULA...ACTIVITY IS LIKELY TO DEVELOP ALONG THE
E COAST. LARGE DOWNDRAFT CAPE WILL DEVELOP THIS AFTERNOON WITH STEEP
LOW LEVEL LAPSE RATES. MODERATE NWLY WINDS OF 30-40 KT EXIST IN THE
MID LEVELS. THUS...ONCE STORMS INITIATE...THEY WILL LIKELY
DRIFT/PROPAGATE S TO SW...WITH A DAMAGING WIND THREAT. SOME SMALL
HAIL WOULD BE LIKELY AS WELL WITH THE STRONGEST CORES...ALTHOUGH NOT
THE PRIMARY THREAT.

..JEWELL.. 06/22/2009
890. Cavin Rawlins
4:33 PM GMT on June 22, 2009
Quoting hurricane2009:
vorticity is actually better over mainland Mexico than the BOC, that should tell you something right there



???

Member Since: July 24, 2005 Posts: 407 Comments: 19076
889. Cavin Rawlins
4:31 PM GMT on June 22, 2009
Also, Andres Update

Member Since: July 24, 2005 Posts: 407 Comments: 19076
887. Orcasystems
4:29 PM GMT on June 22, 2009
Quoting reedzone:


In my eyes, it is, has good vorcity, circulation, convection sustained, and in marginally favorable conditions.. It's an invest to me.



200mb Vorticity - North Atlantic - Latest Available - Large Scale

Member Since: October 1, 2007 Posts: 81 Comments: 26493
886. futuremet
4:27 PM GMT on June 22, 2009
Quoting WxLogic:


Hehe... indeed.


Looking at the 12Z models, it seems that they have a hard time initializing this.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
885. KEEPEROFTHEGATE (Mod)
4:26 PM GMT on June 22, 2009
Quoting Orcasystems:


ROFL, smarta**
Has the garbage started to stack up yet.. did they go on strike?
yeah there on strike but garbage is pick up here at the building by a private company only effect is the wait getting in to offload at the city run transfer stations
Member Since: July 15, 2006 Posts: 163 Comments: 52173
884. Unfriendly
4:23 PM GMT on June 22, 2009
Quoting Orcasystems:


I knew who you were talking about.. the two Lefties :)


two lefties make a right, right?
Member Since: July 21, 2008 Posts: 0 Comments: 291
883. reedzone
4:23 PM GMT on June 22, 2009
Quoting hurricane2009:


It is not an invest, lets not pretend it is lol


In my eyes, it is, has good vorcity, circulation, convection sustained, and in marginally favorable conditions.. It's an invest to me.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
881. WxLogic
4:20 PM GMT on June 22, 2009
Quoting futuremet:
The 00z and 06z GFS are expecting the A/B high weaker compared to the previous runs. This would induce cause more moisture to advect northward. This also in consensus with what the NOGAPS has been indicating. It will interesting to see how the 12z GFS handles this.


Hehe... indeed.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
880. Orcasystems
4:19 PM GMT on June 22, 2009
Quoting KEEPEROFTHEGATE:
if ya really want to contact the NHC here's email address

For general questions, comments, or feedback on tropical cyclones and the NHC contact our Public Relations Officer at
nhc.public.affairs@noaa.gov

just tell em orca sent ya


ROFL, smarta**
Has the garbage started to stack up yet.. did they go on strike?
Member Since: October 1, 2007 Posts: 81 Comments: 26493
879. reedzone
4:19 PM GMT on June 22, 2009
Actually wow, if you look at it from a far point, it looks like a TD, interesting, but no low level circulation yet, very impressive INVEST area.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
878. Cavin Rawlins
4:18 PM GMT on June 22, 2009
Good Afternoon;

Tropical Update
Member Since: July 24, 2005 Posts: 407 Comments: 19076
877. IKE
4:16 PM GMT on June 22, 2009
Quoting gulfcoastdweller:


not fair!!! you have a tiny breeze lol!


I don't live there....I'm in Defuniak Springs,FL......

Member Since: June 9, 2005 Posts: 23 Comments: 37858
875. AussieStorm
4:13 PM GMT on June 22, 2009
Current SAL

Member Since: September 30, 2007 Posts: 9 Comments: 15742
874. RitaEvac
4:13 PM GMT on June 22, 2009
Quoting Orcasystems:


Tagged an invest based on?
The requirements to be designated an Invest are grey at best. Since you agree it has no possibility at this time of ever getting rated higher then an invest.. why name it?



Think reason they wont call it invest is because its going to be on land shortly, so it doesnt warrant any potential development beyond 24-48 hrs. It is an invest but it wont exist in 24-48 hrs so.... think thats their criteria.
Member Since: July 14, 2008 Posts: 1 Comments: 9625
872. KEEPEROFTHEGATE (Mod)
4:11 PM GMT on June 22, 2009
if ya really want to contact the NHC here's email address

For general questions, comments, or feedback on tropical cyclones and the NHC contact our Public Relations Officer at
nhc.public.affairs@noaa.gov

just tell em orca sent ya
Member Since: July 15, 2006 Posts: 163 Comments: 52173
871. Orcasystems
4:10 PM GMT on June 22, 2009
Quoting reedzone:
It's not a matter of knowledge, heck even Levi believes that there being way too conservative this year. Of course there smarter then me, I'm only 20 years old, they have degrees and experience. Though that area in the BOC should at least be tagged an invest, but JUST an invest, it should make landfall before anything else happens.


Tagged an invest based on?
The requirements to be designated an Invest are grey at best. Since you agree it has no possibility at this time of ever getting rated higher then an invest.. why name it?

Member Since: October 1, 2007 Posts: 81 Comments: 26493
870. futuremet
4:08 PM GMT on June 22, 2009
The 00z and 06z GFS are expecting the A/B high weaker compared to the previous runs. This would induce cause more moisture to advect northward. This also in consensus with what the NOGAPS has been indicating. It will interesting to see how the 12z GFS handles this.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
869. reedzone
4:06 PM GMT on June 22, 2009
It's not a matter of knowledge, heck even Levi believes that there being way too conservative this year. Of course there smarter then me, I'm only 20 years old, they have degrees and experience. Though that area in the BOC should at least be tagged an invest, but JUST an invest, it should make landfall before anything else happens.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
868. msphar
4:04 PM GMT on June 22, 2009
Blob approaching Barbados remains my concern after a little shuteye this AM. That blob keeping chugging forward in strong shear. Barbados and Trinidad should be wet tonight.
Member Since: August 20, 2006 Posts: 0 Comments: 289
866. Orcasystems
4:01 PM GMT on June 22, 2009
Quoting reedzone:
I know this won't develop but the area in the BOC should at least be worthy of an Invest. The NHC needs to stop the constant nonsense now.


That appears to be part of the problem, the NHC is not as smart as you. You might want to give them a call and offer your assistance.

Member Since: October 1, 2007 Posts: 81 Comments: 26493
865. reedzone
3:59 PM GMT on June 22, 2009
I know this won't develop but the area in the BOC should at least be worthy of an Invest. The NHC needs to stop the constant nonsense now.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
864. Orcasystems
3:57 PM GMT on June 22, 2009
Quoting hurricane2009:
I was talking about Phil, I like Mike Weir too though


I knew who you were talking about.. the two Lefties :)
Member Since: October 1, 2007 Posts: 81 Comments: 26493
863. IKE
3:57 PM GMT on June 22, 2009
City about 100 miles NNW of Andres....

"Ixtapa Zihuatanejo, MX (Airport)
Updated: 1 hr 8 min 54 sec ago
Rain
81 °F
Rain
Humidity: 84%
Dew Point: 75 °F
Wind: 7 mph from the South
Pressure: 29.63 in (Rising)
Heat Index: 86 °F
Visibility: 3.0 miles
UV: 1 out of 16
Clouds:
Mostly Cloudy 1000 ft
Overcast 8000 ft
(Above Ground Level)
Elevation: 20 ft"
Member Since: June 9, 2005 Posts: 23 Comments: 37858
861. Orcasystems
3:54 PM GMT on June 22, 2009
Quoting leftovers:
the canadian cant buy a putt. nickle got it in the bag.


I don't know... he is known for chocking in this Open.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
859. F1or1d1an
3:52 PM GMT on June 22, 2009
No better over here in NOLA, Ike. Felt like I had to change shirts after I walked 3 blocks from the parking lot to the office.
858. Orcasystems
3:51 PM GMT on June 22, 2009
Quoting hurricane2009:
Lefty just hit an eagle on 13 to tie for the lead


Hmm and my lefty is missing Birdie putts left right and centre (well maybe not centre or it would be in).... sheesh.
Member Since: October 1, 2007 Posts: 81 Comments: 26493
857. CycloneOz
3:49 PM GMT on June 22, 2009
Quoting hurricane2009:
Lefty just hit an eagle on 13 to tie for the lead


That's going to make the Canadians here very happy that Mike's got it goin'...

Unless the "lefty" you're talkin' about is Phil baby...

That would make me very happy! :)
Member Since: August 26, 2006 Posts: 10 Comments: 3420
855. jeffs713
3:40 PM GMT on June 22, 2009
Thanks for the links StormW and BoynSea!

Looking at both of those, *IF* the BOC blob does develop into anything (keep in mind its under marginal shear of 10-20 kts), it will be steered right into the northern Mexico or southern Texas coasts pretty quick. IMO, that is a good thing, since both of those areas desparately need the rain. (especially south Texas... they are in "exceptional drought" conditions)
Member Since: August 3, 2008 Posts: 16 Comments: 5792
854. Orcasystems
3:38 PM GMT on June 22, 2009
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: 26493
851. sporteguy03
3:35 PM GMT on June 22, 2009
Quoting IKE:


Drink plenty of water!

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE MELBOURNE FL
252 AM EDT MON JUN 22 2009

...HOT TEMPERATURES AND HIGH HEAT INDICES EXPECTED AGAIN MONDAY...


Ike, yes I am drinking 4-5 gallons a day it seems, my location 102 degrees 38% humidity.
Member Since: July 7, 2005 Posts: 0 Comments: 5120
850. IKE
I've got 95.0 and sunny.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
849. IKE
""""NATIONAL WEATHER SERVICE TALLAHASSEE FL
935 AM EDT MON JUN 22 2009

...HEAT ADVISORY IN EFFECT FOR SOUTHEAST ALABAMA...AND THE FLORIDA
PANHANDLE THIS AFTERNOON...

.UPDATE...THE MORNING WATER VAPOR IMAGERY DEPICTS THE MEAN MID/UPPER
LEVEL RIDGE CENTERED OVER THE LOWER MS VALLEY...WITH TROUGHS OVER
THE PACIFIC NW AND OFF THE ERN SEABOARD. A STATIONARY FRONT WAS
ORIENTED NW-SE FROM THE IN/IL BORDER THRU CNTRL KY/TN TO ERN GA. A
SMALL MCS WAS MOVING SEWD FROM SRN IN INTO NRN KY...WITH SCATTERED
CONVECTION FROM SRN KY INTO ERN TN.

THE 12Z TAE SOUNDING REVEALED A PRECIP WATER VALUE OF 1.25"...LI -7
AND CAPE OF 5200 J/KG. MODIFYING THE SOUNDING FOR AN AFTN SURFACE
PARCEL OF 101/67 YIELDS MLCAPE 800 J/KG...SBCAPE 2060 J/KG...LI -3.5
AND PRECIP WATER 1.19". THESE MODIFIED VALUES ARE ACTUALLY A LITTLE
LOWER THAN YESTERDAY. THE 22/00Z LOCAL WRF MODEL PRECIP FCST
DEVELOPS CONVECTION OVER AREAS EAST OF A LINE FROM ALBANY TO
THOMASVILLE GA...AND OVER THE SUWANNEE VALLEY DURING THE MID-LATE
AFTN. RUC CORFIDI VECTORS BRING SMALL MCS S-SE INTO OUR GA/BIG BEND
ZONES DURING THE EVENING. THE MEAN 1000-700 MB SYNOPTIC FLOW TODAY
IS A 9 OR N-NW GREATER THAN 10 KT. WITH MODIFIED CAPE AND PRECIP
WATER VALUES FOR THIS REGIME A STANDARD DEVIATION BELOW CLIMO...HAVE
LOWERED TODAY/S POPS SLIGHTLY...FROM SILENT 10S SE AL/FL PANHANDLE
TO 30 PERCENT S/CNTRL GA/ERN FL BIG BEND. WILL HAVE TO MONITOR
ACTIVITY UPSTREAM OVER THE TN VALLEY TODAY AS IT MOVES INTO NRN GA
THIS AFTN WHERE SPC HAS HIGHLIGHTED WITH A SLIGHT RISK FOR SEVERE
WEATHER.

IT WILL BE ANOTHER HOT AND HUMID DAY...WITH TLH LIKELY TO EXTEND ITS
STRING OF 100+ DEGREE DAYS TO SEVEN. WITH THE RIDGE SLIGHTLY WEST OF
YESTERDAY/S POSITION...OUR WRN ZONES WILL BE EXPERIENCING THE MORE
DANGEROUS HEAT INDICES UP TO NEAR 110 THIS AFTN.
RAISED MAX TEMPS A
DEGREE OR TWO FOR ALL EXCEPT ERN ZONES.""""..........


Pitiful.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Jeff:

Try this.

BoynSea

Link
Member Since: Posts: Comments:
846. IKE
Quoting sporteguy03:


if it keeps moving great slows down and dumps heavy rain no good!


Drink plenty of water!

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE MELBOURNE FL
252 AM EDT MON JUN 22 2009

...HOT TEMPERATURES AND HIGH HEAT INDICES EXPECTED AGAIN MONDAY...
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Taiwan threatened...again...

Member Since: Posts: Comments:
844. IKE
Quoting KEEPEROFTHEGATE:
thats a go my friend and you shall be replaced with empty space just like whats in your head


LOL!
Member Since: June 9, 2005 Posts: 23 Comments: 37858

Viewing: 894 - 844

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 JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.