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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last year someone gave us a link to a monthly sst data chart where you could see the average temps for any given month that went back several years...does anyone have the link???
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1493. KEEPEROFTHEGATE (Mod)
guess not

brb got to go again
Member Since: July 15, 2006 Posts: 163 Comments: 52248
Adrian, mail.
Member Since: June 9, 2007 Posts: 4 Comments: 15718
1490. KEEPEROFTHEGATE (Mod)
had to step out emer.in building
do we have a cane yet before i check
Member Since: July 15, 2006 Posts: 163 Comments: 52248
1489. Ossqss
Quoting vortfix:
WOW! Quick dinner!!


Yeah...he's just a kid!
His Mommy fed him again tonight!


And H23...please stop plagiarizing!



I hope your evening gets better .
Member Since: June 12, 2005 Posts: 6 Comments: 8183
As i stated earlier today It is that period from August 20th thru Sept. 2Oth. that is critical. If a ridge just happens to set up in the Western Atlantic at 500 mb during that period, there will likely be landfalls.
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1487. Levi32
Quoting stillwaiting:



part of the mjo pulse moving into the southern GOM????


Well we can't really attribute one small cluster of thunderstorms directly to a global-scale pattern like that. What we can attribute to the MJO is the large area of upward motion and heat build-up in the east Pacific that produced TS Andres.
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I do think the Nino will win out in SEPT or OCT/NOV timeframe , right after the peak of season, thus the 'shearing' increase in the Atlantic basin will NOT be impacted until late season.

hmmm....Interesting change of thought.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1485. vortfix
WOW! Quick dinner!!


Yeah...he's just a kid!
His Mommy fed him again tonight!


And H23...please stop plagiarizing!

1484. Levi32
Quoting StormW:


WOW! Quick dinner!!


Haha it was only a bowl of soup and everyone else had already eaten =)
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Quoting Levi32:


I'm not sure what you mean. The area of thunderstorms near the NW Yucatan are mainly initiating over land and are being enhanced by a divergent flow aloft. I don't see anything significant about it.



part of the mjo pulse moving into the southern GOM????
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Thought i'd repost this incase it was missed.

A few thoughts on steering and enso across the ATL.

I think the 09 ATL season will boil down to warming SST trends in the Atlantic, and the developing Nino ( 0.7 today), but tri monthly ONI is still near 0.0 or neutral.

I do think the Nino will win out in SEPT or OCT/NOV timeframe , right after the peak of season, thus the 'shearing' increase in the Atlantic basin will NOT be impacted until late season.

2 areas to watch - The Southern US ridge and the Bermuda ridge. The southern US ridge has been in place for the past 3-4 weeks and will oscillate between centered over TX/S. Plains and the Southeast or the SW US. When it is over TX, the GUlf will be closed for business and storms will deflect into MX or elsewhere (unless one forms under the ridge inth GOM which is very possible).

The 2nd area is the Bermuda ridge which is displaced farther to the EAST now, meaning 'recurve' potential is high for the next 6 weeks or so.

Eventually, it is the breakdown of the Southern ridge (aug/sep) as seasonal impacts begin to weaken the strength of the ridge, and the location of the mean AUG/SEP trough which I still think is Midwest/OValley...then that opens up the E GOM and the E coast for any tropical threats which won't be until AUG/SEP at earliest.

Have a great night. Adrian

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1480. Levi32
Quoting StormW:


Just curious...however I think the flow aloft may be more confluent now.


Ok lol. Well there's strong confluence to the north of it. I noticed that the upper-level flow associated with all these upper features are forming what almost looks like an inverted "v" trough of sorts oriented SE to NW from the western Caribbean up through the Yucatan and extending into the western Gulf of Mexico. That's setting up the convergence and divergence zones.

Alright I'm over-analyzing just trying to find out why you asked that lol.

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1479. Dr3w
Quoting Levi32:


Well there will be a couple things to watch later this week. First the trough split which will be occuring in the Gulf of Mexico and an area of low pressure forecasted to form over the north gulf coast that might get drawn SW over the gulf by the upper feature. The models aren't showing much but it's worth watching for mischief.

The 2nd area is the western Caribbean where the GFS is forecasting a surface trough to form in 3-5 days. After the TUTT (tropical upper tropospheric trough) splits over the Gulf of Mexico an upper ridge will build northwestward over the western Caribbean which will provide a more favorable upper-level environment. A tropical wave currently approaching the windward islands will also be moving into the SW Caribbean around that time.

So there's your "chances". We'll have to see how things evolve this week.


thanks for explaining that all to me levi =]
this is the surface area to watch for a possiblity of a invest over the next 24-36hrs as it drifts north then possibly NE,IMO
Member Since: October 5, 2007 Posts: 20 Comments: 4970
1476. Levi32
Quoting Dr3w:
Levi when do you think we will see a chance of something developing


Well there will be a couple things to watch later this week. First the trough split which will be occuring in the Gulf of Mexico and an area of low pressure forecasted to form over the north gulf coast that might get drawn SW over the gulf by the upper feature. The models aren't showing much but it's worth watching for mischief.

The 2nd area is the western Caribbean where the GFS is forecasting a surface trough to form in 3-5 days. After the TUTT (tropical upper tropospheric trough) splits over the Gulf of Mexico an upper ridge will build northwestward over the western Caribbean which will provide a more favorable upper-level environment. A tropical wave currently approaching the windward islands will also be moving into the SW Caribbean around that time.

So there's your "chances". We'll have to see how things evolve this week.
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We musta been right there on that blue frontal boundary...wow!
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Quoting hurricane2009:
BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE MELBOURNE FL
1025 PM EDT MON JUN 22 2009

THE NATIONAL WEATHER SERVICE IN MELBOURNE HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
NORTHEASTERN BREVARD COUNTY IN FLORIDA
SOUTHEASTERN VOLUSIA COUNTY IN FLORIDA


* UNTIL 1115 PM EDT.

* AT 1022 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN
EXCESS OF 58 MPH. THIS STORM WAS LOCATED NEAR BETHUNE BEACH...OR
ABOUT 5 MILES EAST OF EDGEWATER...AND MOVING SOUTHEAST AT 30 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE...BUT ARE NOT LIMITED TO...
ELDORA...APOLLO BEACH...OAK HILL...SCOTTSMOOR...HAULOVER CANAL...
KLONDIKE BEACH...MERRITT ISLAND WILDLIFE REFUGE...PLAYALINDA
BEACH...PORT CANAVERAL...MERRITT ISLAND...CAPE CANAVERAL...KENNEDY
SPACE CENTER AND COCOA BEACH.

I just rode my motorcycle home from dinner in that...it was preettty bad.
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Quoting hurricane2009:
Great thanks I am in the area of greatest severe threat



I am afraid to ask.. in weather terminology... what is the difference between "Severe Threat" and "Greater Severe Threat", that would sort of make one believe that there must be a "Lesser Severe Threat"
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just got slammed with this blob...

...now that was a wild motorcycle ride home.
And when I got here, poor Archie had to go out and pee in it!
Brave dog.
wow. that was a pretty strong cell that just moved through here.
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Thanks Adrian. Your insight is greatly appreciated
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1467. hahaguy
Great info Adrian.
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1466. vortfix



MESOSCALE DISCUSSION 1279
NWS STORM PREDICTION CENTER NORMAN OK
0932 PM CDT MON JUN 22 2009

AREAS AFFECTED...NRN AND CNTRL FL

CONCERNING...SEVERE THUNDERSTORM WATCH 493...

VALID 230232Z - 230330Z

CORRECTED FOR ATTN HEADER

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 493
CONTINUES.

THE THREAT FOR ISOLATED DAMAGING WIND AND HAIL CONTINUES PRIMARILY
ALONG THE ERN THIRD OF WW 493. CONFIDENCE IS NOT PARTICULARLY HIGH
THAT SUSTAINED...ROBUST STORMS WILL DEVELOP IN WRN PORTIONS OF WW.

A SWD MOVING CONVECTIVE OUTFLOW BOUNDARY EXTENDS FROM ABOUT 50 SM N
OF CAPE CANAVERAL NWWD TO ABOUT 50 SM EAST OF TALLAHASSEE. MODERATE
INSTABILITY PERSISTS SOUTH OF THIS BOUNDARY WITH MLCAPE FROM AROUND
1500 J/KG ALONG THE E-CNTRL FL COAST TO 2500 J/KG ALONG THE W CNTRL
COAST. PRIMARY THUNDERSTORM DEVELOPMENT REMAINS OVER THE E CNTRL
COAST WITHIN ZONE OF ENHANCED CONVERGENCE AND LIFT WHERE THE SWD
MOVING OUTFLOW BOUNDARY IS INTERSECTING THE SEA-BREEZE BOUNDARY. THE
OUTFLOW BOUNDARY REMAINS SKELETAL FARTHER WEST THROUGH THE REMAINDER
OF N CNTRL FL. THE 00Z RAOB FROM TAMPA INDICATES AN INVERSION BASED
AROUND 850 MB...AND AS THE BOUNDARY LAYER COOLS...SURFACE BASED
CONVECTIVE INHIBITION WILL LIKELY CONTINUE TO INCREASE. WRN END OF
OUTFLOW BOUNDARY IS NOT BEING REINFORCED BY ONGOING STORMS AND WILL
LIKELY WEAKEN. THIS IN CONJUNCTION WITH THE STABILIZING BOUNDARY
LAYER SUGGEST IT MAY BE DIFFICULT TO INITIATE ROBUST STORMS IN WRN
HALF OF WW 493.

..DIAL.. 06/23/2009

1465. HadesGodWyvern (Mod)


hmm...
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A few thoughts on steering and enso across the ATL.

I think the 09 ATL season will boil down to warming SST trends in the Atlantic, and the developing Nino ( 0.7 today), but tri monthly ONI is still near 0.0 or neutral.

I do think the Nino will win out in SEPT or OCT/NOV timeframe , right after the peak of season, thus the 'shearing' increase in the Atlantic basin will NOT be impacted until late season.

2 areas to watch - The Southern US ridge and the Bermuda ridge. The southern US ridge has been in place for the past 3-4 weeks and will oscillate between centered over TX/S. Plains and the Southeast or the SW US. When it is over TX, the GUlf will be closed for business and storms will deflect into MX or elsewhere (unless one forms under the ridge inth GOM which is very possible).

The 2nd area is the Bermuda ridge which is displaced farther to the EAST now, meaning 'recurve' potential is high for the next 6 weeks or so.

Eventually, it is the breakdown of the Southern ridge (aug/sep) as seasonal impacts begin to weaken the strength of the ridge, and the location of the mean AUG/SEP trough which I still think is Midwest/OValley...then that opens up the E GOM and the E coast for any tropical threats which won't be until AUG/SEP at earliest.

Adrian
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1462. vortfix
One more time!



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.


1461. Dr3w
Levi when do you think we will see a chance of something developing
1459. Levi32
Back after dinner.
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1458. vortfix



It is not happening!


AOI #1

AOI #2
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Super Hi-res image of Andres
Member Since: June 9, 2007 Posts: 4 Comments: 15718
1455. bappit
Here's something to consider in your hurricane preparations. Haven't seen it mentioned on this blog ever.

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Quoting Ossqss:
Looks like its gettin impacted
Looks like it is getting sandwiched between southwest and northeast winds.
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1452. Levi32
Quoting StormW:


Levi,
What do you think about just coming off the NW Yucatan Peninsula? Just wanted to hear your thought.


I'm not sure what you mean. The area of thunderstorms near the NW Yucatan are mainly initiating over land and are being enhanced by a divergent flow aloft. I don't see anything significant about it.
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Quoting stillwaiting:
there seems to be a good amount of instability moving from the atlantic westward accross the coastline and eventually into the GOM,my home barometer is at 1008mb,pressures have been lowering and rainfall over most of the peninsula from now thru tommorow afternoon seems iminent,IMO....lots of lighning w/these storms overnight into the morning..
I'm right on the Atlantic Coast and there is a good amount of lightning and occasional grumbling in the distance. We had a pretty good T-storm with a special marine warning issued for that cell but that's about it.
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1450. Ossqss
Looks like its gettin impacted
Member Since: June 12, 2005 Posts: 6 Comments: 8183
1449. HadesGodWyvern (Mod)
Joint Typhoon Warning Center
Tropical Cyclone Formation Alert
01:30 AM UTC June 23 2009
====================================

An area of convection (93A) located at 19.3N 71.4E or 85 NM west-northwest of Mumbai, India. Animated enhanced infrared imagery and a 1611z ASCAT pass indicates that a low level circulation center has continued to develop over the past 12 hours with deep convection moving over the low level circulation center. Upper level analysis shows a dual channel outflow beginning to setup over the low level circulation center, enhanced by a mid-latitude upper level trough over the Pakistan/India border. This will allow for an increase in intensity over the next 12-24 hours, Additionally it is in low vertical wind shear however if the system continues to track toward the coast, land influences could hamper the inflow to the low level circulation center. Sea surface temperature are favorable for development throughout the region. Intensity estimates are based on Dvorak estimates from PGTW an KNES.

Maximum sustained winds near the center is 27-32 knots with a minimum sea level pressure of 1001 MB. Due to increased consolidation and organization over the past 6 hours, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is UPGRADED TO GOOD
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1448. vortfix
Climatologically speaking the BOC is a favored area for development in June.

But this is not it!

1447. vortfix
Is this what y'all think might develop??






there seems to be a good amount of instability moving from the atlantic westward accross the coastline and eventually into the GOM,my home barometer is at 1008mb,pressures have been lowering and rainfall over most of the peninsula from now thru tommorow afternoon seems iminent,IMO....lots of lighning w/these storms overnight into the morning..
Member Since: October 5, 2007 Posts: 20 Comments: 4970
1445. WAHA
Quoting hurricane2009:
maybe the remnants of Karen care help the BOC area flare up LOL

Too late; Noel did that in 2007, and I seriously doubt that Karen would take a toll on this system.
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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.

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