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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CHGE77

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

1222 UTC SUN JUN 21 2009



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



EAST PACIFIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (EP932009) 20090621 1200 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

090621 1200 090622 0000 090622 1200 090623 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 14.7N 100.3W 15.0N 100.7W 15.6N 101.2W 16.3N 101.7W

BAMD 14.7N 100.3W 14.9N 101.0W 15.4N 101.8W 16.2N 102.6W

BAMM 14.7N 100.3W 15.1N 100.9W 15.6N 101.5W 16.4N 102.2W

LBAR 14.7N 100.3W 15.2N 101.3W 15.8N 102.6W 16.9N 104.2W

SHIP 25KTS 30KTS 38KTS 47KTS

DSHP 25KTS 30KTS 38KTS 47KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

090623 1200 090624 1200 090625 1200 090626 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 17.1N 102.5W 18.7N 104.8W 19.0N 107.5W 19.5N 111.3W

BAMD 17.2N 103.9W 18.9N 107.5W 19.5N 112.1W 19.8N 117.4W

BAMM 17.3N 103.3W 19.0N 106.4W 19.3N 110.4W 19.5N 115.4W

LBAR 18.2N 106.0W 21.7N 109.7W 24.9N 112.7W 27.5N 114.2W

SHIP 56KTS 64KTS 59KTS 53KTS

DSHP 56KTS 64KTS 59KTS 53KTS
Member Since: July 15, 2006 Posts: 176 Comments: 55517


Click to enlarge
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Quoting Ossqss:
Bradenton FL

90.9 °F
Scattered Clouds
Humidity: 25%
Dew Point: 50 °F

The Humidity was 82% yesterday. Not sure what happened, but I like the lower number much more.

At what times of the day were the different humidity readings taken ? Dewpoint of 50 seems a little low for yesterday's weather conditions. Current Florida dewpoints are in the upper 70s to low 80s with 60s reaching up to the mid-atlantic.
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typo:I ment a TS by tommorow morning,its a TD now,110%,it'll be posted in the 2pm,IMO
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Member Since: September 30, 2007 Posts: 9 Comments: 15962
Quoting stillwaiting:




looking out about96-144hrs for possible significant development,IMO,maybe a TD by tommorow morning...
Have you looked at it recently ? I think sometime today. Sure hope it doesn't pull an Alma on us.
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338. IKE
That 1008 mb low is parked about right over me....I don't spell relief R O L A I D S....I spell it L O W.

:)

NAM @ 72 hours...
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Good morning everyone it looks like another very hot day in FL today.
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Quoting stormwatcherCI:
It actually looks very healthy compared to some of the "almost"TS so far.




looking out about96-144hrs for possible significant development(hurricane),IMO,maybe a TS by tommorow morning...
Member Since: October 5, 2007 Posts: 20 Comments: 4970
335. IKE
Quoting sporteguy03:
Ike
You are under a red flag warning too


LOL.

The only thing on fire outside is that egg I dropped on the cement bringing groceries in.

I'll alert the neighbors though....thanks....
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Tropical Update

Member Since: July 24, 2005 Posts: 407 Comments: 19076
East End,Grand Cayman/ Temp 93 Humidity 76% Heat index 103.
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Ike
You are under a red flag warning too
Member Since: July 7, 2005 Posts: 0 Comments: 5417
Milton Fl 94 degrees = 102 degrees heat index @ 10:18 am
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Quoting stillwaiting:



this could very well be the first hurricane of the 2009 season for either basin,IMO
It actually looks very healthy compared to some of the "almost"TS so far.
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Bradenton FL

90.9 °F
Scattered Clouds
Humidity: 25%
Dew Point: 50 °F

The Humidity was 82% yesterday. Not sure what happened, but I like the lower number much more.
Member Since: June 12, 2005 Posts: 6 Comments: 8188
Quoting stormwatcherCI:
FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

SPECIAL OUTLOOK ISSUED TO UPDATE DISCUSSION OF LOW PRESSURE AREA
SOUTH OF ACAPULCO MEXICO.

UPDATED...SATELLITE IMAGES INDICATE THAT SHOWERS AND THUNDERSTORMS
ASSOCIATED WITH THE AREA OF LOW PRESSURE CENTERED ABOUT 150 MILES
SOUTHWEST OF ACAPULCO MEXICO CONTINUE TO BECOME BETTER ORGANIZED...
BUT THE LOW-LEVEL CENTER OF CIRCULATION IS NOT YET WELL-DEFINED.
ONLY A SLIGHT INCREASE IN THE ORGANIZATION OF THIS SYSTEM WOULD
RESULT IN THE FORMATION OF A TROPICAL DEPRESSION...AND ADVISORIES
COULD BE INITIATED LATER TODAY. THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS. HEAVY RAINS COULD AFFECT PORTIONS OF THE
SOUTHERN AND SOUTHWESTERN COAST OF MEXICO DURING THE NEXT DAY OR
TWO...AND INTERESTS IN THIS REGION SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.



this could very well be the first hurricane of the 2009 season for either basin,IMO
Member Since: October 5, 2007 Posts: 20 Comments: 4970
327. IKE
Help is on the way.....12Z NAM @ 60 hours....

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326. IKE
PWS about 6 miles from where I sit....at 10:13 in the morning.

"WZEP AM 1460 DeFuniak Springs, FL, DeFuniak Springs, Florida (PWS)
Updated: 3 sec ago
Clear
92.9 °F

Clear
Humidity: 57%
Dew Point: 75 °F
Wind: 0.0 mph
Wind Gust: 4.0 mph
Pressure: 29.86 in (Falling)
Heat Index: 105 °F
Visibility: 10.0 miles
UV: 8 out of 16
Clouds:
Clear -
(Above Ground Level)
Elevation: 174 ft"
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325. IKE
Looks like the heat dome of high pressure in the NE GOM is starting to retreat to the west. You can see on visible satellite how the trough coming down is beginning to force the high west.

My thermometer says 94.8 right now...outside my window....
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GOM continues to warm.

Member Since: Posts: Comments:
FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

SPECIAL OUTLOOK ISSUED TO UPDATE DISCUSSION OF LOW PRESSURE AREA
SOUTH OF ACAPULCO MEXICO.

UPDATED...SATELLITE IMAGES INDICATE THAT SHOWERS AND THUNDERSTORMS
ASSOCIATED WITH THE AREA OF LOW PRESSURE CENTERED ABOUT 150 MILES
SOUTHWEST OF ACAPULCO MEXICO CONTINUE TO BECOME BETTER ORGANIZED...
BUT THE LOW-LEVEL CENTER OF CIRCULATION IS NOT YET WELL-DEFINED.
ONLY A SLIGHT INCREASE IN THE ORGANIZATION OF THIS SYSTEM WOULD
RESULT IN THE FORMATION OF A TROPICAL DEPRESSION...AND ADVISORIES
COULD BE INITIATED LATER TODAY. THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS. HEAVY RAINS COULD AFFECT PORTIONS OF THE
SOUTHERN AND SOUTHWESTERN COAST OF MEXICO DURING THE NEXT DAY OR
TWO...AND INTERESTS IN THIS REGION SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.
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One hell of a pulse on the GFS.

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Quoting IKE:


I had a good one too...use to take me to sporting events a lot...PGA...Juco basketball...Astrodome....

25 years is a l-o-n-g time........


I can't remember how many MLB games my Dad took us kids too.....WOW! Did we have a blast. The fishing trips were unreal...Dad watched every High School Event i played in....Didn't miss a single thing. When i played College Baseball he drove miles just to watch me play.....He was an amazing Father that i miss!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Happy Fathers Day !

No anonymous cards this year ! Pheew :)
Member Since: June 12, 2005 Posts: 6 Comments: 8188
319. IKE
Quoting TampaSpin:


Ya i hear ya IKE....My Dad died December 4, 2006! Never gave him enough HUGS! I wish i had!


I had a good one too...use to take me to sporting events a lot...PGA...Juco basketball...Astrodome....

25 years is a l-o-n-g time........
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Quoting IKE:


My dad has been dead for nearly 25 years. If he were alive today, he would be in his late 90's.



Ya i hear ya IKE....My Dad died December 4, 2006! Never gave him enough HUGS! I wish i had!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
317. IKE
Quoting TampaSpin:
If you have a Father. Make sure you treat him with a HUG and Just a Little Love! Amazing what a Little Does! HAPPY FATHERS DAY!


My dad has been dead for nearly 25 years. If he were alive today, he would be in his late 90's.

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If you have a Father. Make sure you treat him with a HUG and Just a Little Love! Amazing what a Little Does! HAPPY FATHERS DAY!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Barrow Alaska,

Length Of Visible Light: 24h 00m
Length of Day 24h 00m
Tomorrow will be 0m 0s shorter.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
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313. IKE
Barrow/Wiley Post 05:53 Light Snow Fog/Mist 30 E 18


Snow and 30 w/a gusty wind at Barrow.

Good morning northern slope!
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Quoting futuremet:
Starting tomorrow, darkness will start overpowering light.



tell that to the people of siberia and alaska,lol...still plenty of sunny days up there,lol:)
Member Since: October 5, 2007 Posts: 20 Comments: 4970
311. ackee
DO u guys notice that most of the major models has been wrong so far with there tropical development for june
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Starting tomorrow, darkness will start overpowering light.
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It is really early in the season.... I hope people don't let their guard down. Even if only 5 or 6 storms were to form, the SST in the GOM will supply a lot of fuel for those storms that make it into the region. The longer the High pressure system stays in place, the "Hotter" the water will get. JMO
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Quoting msphar:
Summer soltice in the NH and not much going on in the Atlantic MDR yet. Sweet.


there's a lag between TC development/higher sst's and the earths tilt(summer solstice),resulting in a higher # of TC's in august and september as the equinox arrives....in other words the sun is at its highest point North in the northern hemsiphere,but the sun continues to warm the waters for another 2 months as the earth tilts slowly back towards equinox...the game is just begining and this is not a slow start to the season,either average or what I believe:above average,we've already had a td and a un-named TS,IMO...
Member Since: October 5, 2007 Posts: 20 Comments: 4970
307. IKE
Quoting presslord:


Oh no, sir...I've told you...this is bikini weather...


LOL.
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Hmmm... less dust... interesting.

Well, June 20th and still no named storm. I wonder when we'll get Ana already.

I think maybe by July 5th or so, we'll have something.

But this dust thing is interesting... I never thought that could be a reason why there are more hurricanes.
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Good morning.

Tropical Update June 21 2009

Visit my blog for more



Video will be IN HD, once finished processing by youtube.
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Quoting IKE:


Will you be there in your hot dress?


Oh no, sir...I've told you...this is bikini weather...
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good morning and happy father's day to all the dad's on the blog
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Whoever the cartographer was who created the "Dust Optical Thickness" map that Dr. Masters used in his post has misspelled Libya. (O the shame! I'm so embarrassed for my profession.)
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Summer soltice in the NH and not much going on in the Atlantic MDR yet. Sweet.
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good morning everyone!!!,welcome to the first day of summer 2009!!!!,although for us in the south its felt like summer for over a month now.....
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting Rodek:
Anyone ever see strange things get carried in by Hurricanes? While living in Ft Walton Beach a short while ago, we saw birds that were carried in by some storms!!!


After the passing of Hurricane Floyd, I found a coconut on the beach of the Jersey Shore!
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Quoting HIEXPRESS:
GM, Happy day to the Fathers(time shifting that holiday here) workin' & lurkin.

I've heard it said that tropical cyclones transport a lot of heat poleward. Don't they just put it right back into the ocean (friction, waves, mixing)? Except for the poleward outflow, and what warm air/vapor is dragged along in the storm, how much heat is actually transported? It seems the ocean currents, and straight line winds do most of the transporting, and can relieve that built up TCHP without all of the drama. Anyone got a link to a page/document with concise #s on ocean vs atmospheric heat transport?


Tropical cyclone help to balance the Earth's heat budget by enhancing the Hadley Circulation. It is not the tropical cyclone itself but the role it plays in the Hadley circulation, where heat store in the tropics, eventually rises and is expelled poleward. Recurving TCs that leave the Hadley circulation do this by a different but less effective process, ie, baroclinic.

The majority of the heat is transported by ocean currents while contribution by tropical cyclones are unquantified.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Happy Father's day to all the WU Dads! Too many to list but thank you!
Member Since: July 7, 2005 Posts: 0 Comments: 5417
Link

Ike check it out!
Looks like an artic blast went through Kissimmee, FL as the low was 33 degrees in the State Extremes in Florida. Kissimmee you mind sharing some of that with the rest of the state, lol.
Member Since: July 7, 2005 Posts: 0 Comments: 5417
GM, Happy day to the Fathers(time shifting that holiday here) workin' & lurkin.

I've heard it said that tropical cyclones transport a lot of heat poleward. Don't they just put it right back into the ocean (friction, waves, mixing)? Except for the poleward outflow, and what warm air/vapor is dragged along in the storm, how much heat is actually transported? It seems the ocean currents, and straight line winds do most of the transporting, and can relieve that built up TCHP without all of the drama. Anyone got a link to a page/document with concise #s on ocean vs atmospheric heat transport?
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294. IKE
Quoting presslord:
Portlight Party and Performance in Houston today...lottsa WU folks there...we'vve sorta come full circle...good times and great fellowship, I'm sure...


Will you be there in your hot dress?
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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.

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