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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244. IKE
I've got 83.8 degrees at 9:50 pm in Defuniak Springs,FL.
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85*F right now in srq w/humidity at 83%,dew point is a steamy 79*F
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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!!!
i remember when i was a boy back in 79 after david pass along newfounland offshore waters the upwelling dragged up some strange stuff from the ocean deeps i seen a viper fish and wolf fish caught in our nets also some type of jelly fish that burned your skin all over the place i was a boy of 14 at the time out fishing with my grandfather on the grand banks on a longliner i remember my grandfathers hands having blisters all over them from whatever it was we were dragging up the wolf fish was scary it was trashing around almost making a barking sound we had to use a grapping hook to get it off the boat i will never forget that as long as i live from there on out i have been interested in storms since
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Station SBPT2 - 8770570 - Sabine Pass North, TX

Conditions at SBPT2 as of
(9:06 pm CDT on 06/20/2009)
0206 GMT on 06/21/2009:

Air Temperature (ATMP): 82.9 °F
Water Temperature (WTMP): 87.8 °F

Good warm evening everyone.
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Quoting Drakoen:
The waters are ripe for tracks near the eastern seaboard.


only place I see thats significantly warmer than 05'is the GS and part of the west atlantic ,the waters in the bahamas and the eastern GOM looks a bit cooler than 05',IMO
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239. IKE
High pressure heat dome finally moving on the 00Z NAM model run.
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at 545 gmt or 2 hrs 17 mins it will be official start of summer and the suns maximum point north will be acheived and slowly starts its southern run back towards the equator tomorow will be the longest daylight of the year for northern hemisphere
Member Since: July 15, 2006 Posts: 168 Comments: 53285
237. 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!!!
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Enough heat already! High, high go away please come back another day. LOL
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235. 7544
well with epac heating up its only a matter of time the gom and carb will be next usally follows the trend saty tuned
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The waters are ripe for tracks near the eastern seaboard.
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Quoting CybrTeddy:

Well I guess the GOMEX is the place to look this season.


The southeastern Atlantic seaboard needs to be careful as well. The Gulfstream has been significantly cooler than normal the past few years, but now it looks like it is warming back up to normal levels. A hot, deep Gulfstream can make a system bomb like nothing else, as storms like Andrew or Hugo can show.
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231. Bonz
Quoting KEEPEROFTHEGATE:
now iam doing the heat dance

lol


OK, you can stop now. Days of 92-95 degree heat gets old real quickly!
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Quoting SavannahStorm:




The Bahamas, Gulfstream, and Eastern GOM are definitely warmer than 2005.

Well I guess the GOMEX is the place to look this season.
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The Bahamas, Gulfstream, and Eastern GOM are definitely warmer than 2005.
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Quoting WeatherStudent:


Really, 456? That's very dangerous, ain't it?
its good if ya want a powerhouse storm a little later down the road hopefully that don't happen but nobody knows for sure we got 164 days to find out
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Quoting WeatherStudent:


Really, 456? That's very dangerous, ain't it?


They are pretty high (near Bahamas/Eastern GOM) but I don't know if they will cool or continue to warm. SSts are dynamic and they can get cooler in 2 weeks time, but with rather cloud free skies, only wind stress could cool those waters.

Also notice the SSTs in the Central Caribbean are relatively cooler (not related to the 2005 map) and that was due to the week-2 weeks long period of convection earlier back.

The MDR is still cooler in 2009 though but troubling in that that is not where we are expecting much development this year. Rather closer to home.



Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting KEEPEROFTHEGATE:
now iam doing the heat dance

lol


You appear to be doing a H*ll of a job :)
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Quoting Orcasystems:
KOG & I spent all winter doing the snow dance for Florida.. we came sooooo close.
now iam doing the heat dance

lol
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Seems to be a wall between the Epac and the GOM/BOC
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KOG & I spent all winter doing the snow dance for Florida.. we came sooooo close.
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hurricane2009,

lol, I actually don't take sides, but at that time, I was commenting on article I was reading.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Swells22:
Thanks for your post, Dr. Masters. Can I ask a stupid question though?

"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."

I thought that an inversion was where you have some warmer air aloft?
sam


Under certain conditions, the normal vertical temperature gradient is inverted such that the air is colder near the surface of the Earth. This can occur when, for example, a warmer, less dense air mass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warm fronts, and also in areas of oceanic upwelling such as along the California coast. With sufficient humidity in the cooler layer, fog is typically present below the inversion cap. An inversion is also produced whenever radiation from the surface of the earth exceeds the amount of radiation received from the sun, which commonly occurs at night, or during the winter when the angle of the sun is very low in the sky. This effect is virtually confined to land regions as the ocean retains heat far longer. In the polar regions during winter, inversions are nearly always present over land.

A warmer air mass moving over a cooler one can "shut off" any convection which may be present in the cooler air mass. This is known as a capping inversion. However, if this cap is broken, either by extreme convection overcoming the cap, or by the lifting effect of a front or a mountain range, the sudden release of bottled-up convective energy — like the bursting of a balloon — can result in severe thunderstorms. Such capping inversions typically precede the development of tornadoes in the midwestern United States. In this instance, the "cooler" layer is actually quite warm, but is still denser and usually cooler than the lower part of the inversion layer capping it.
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Orcasystems,

well probably during the winter of 2007-2008, many palces across the global receive chillin conditions, porbably snow in Iraq is the most striking. Some scientist said La Nina had cooled the global that winter.

Afghanistan's coldest winter kills over 900

And one my favorite blog posts, lol

January Highlights Feb 1 08

Happy February to all!

Lets get down to the nitty gritty. You say Global Warming, I say Global Cooling. January saw much cold winter weather, not just in the United States, but also around the Northern Hemisphere. Parts of the Middle East saw their first snow in history. I witness my first cold front in living memory, and I live in the Caribbean. A cold front was analyzed near 11N in the Tropical Atlantic. Snow flurries were detected on radar just offshore Southeast Florida, just as 08 began. Again, some say Global warming, I say Global cooling.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Thanks for your post, Dr. Masters. Can I ask a stupid question though?

"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."

I thought that an inversion was where you have some warmer air aloft?
sam
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up state ny is just as bad if not worse for winter weather 456 summer can be just as hot or hotter than the tropics come july and august the warmest temp i have ever seen in toronto was aug 2005 when we hit 37c with a heat index of 44c or 110f
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Quoting Weather456:
I wanted to go to Canada in November but not sure. And frankly, the only reason I chose to go school in the Caribbean becuz I cant tolerate cold weather. My other choice was a school in up state New York. Despite this, I would like to see snow

The coldest nights I porbably could of remembered was 2007-2008 and 19C is cold for us.


OK, after that last remark... you deserve Toronto in January. 19C cold... sheesh.

I don't like snow... Victoria is a Weather Anomaly, due to its unique location. We seldom get snow, and when we do it normally gone in a day or two.... last couple years due to ummm GW.. we have been getting some wicked winters??

Normally we can golf year round.
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Quoting Weather456:
I wanted to go to Canada in November but not sure. And frankly, the only reason I chose to go school in the Caribbean becuz I cant tolerate cold weather. My other choice was a school in up state New York. Despite this, I would like to see snow


Finally someone that hates cold weather lol

Most people here enjoy it more than warm weather.
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I wanted to go to Canada in November but not sure. And frankly, the only reason I chose to go school in the Caribbean becuz I cant tolerate cold weather. My other choice was a school in up state New York. Despite this, I would like to see snow

The coldest nights I porbably could of remembered was the winter 2007-2008 and 19C is cold for us.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting KEEPEROFTHEGATE:
you should visit toronto canada in january 456 that would be an experience you will never forget
-20 windchill with 6 ft of snow on the ground ever seen snow up close before 456


Now what did he ever do to deserve that kind of invitation... be nice :)
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AOI #1

AOI #2
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you should visit toronto canada in january 456 that would be an experience you will never forget
-20 windchill with 6 ft of snow on the ground ever seen snow up close before 456
Member Since: July 15, 2006 Posts: 168 Comments: 53285
You would not believe warmer than June 17 2005.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
The Gulf and especially the Bahamian waters are really hot!
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When I travel, I like compare countries. neva been 2 the United States :(. But the first thing on my list when I do go, if possible, is to visit the NHC.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
sounds like it was very informative 456 glad ya had a good trip are ya home now or still there
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Quoting KEEPEROFTHEGATE:
evening 456 did you enjoy your little trip


Barbados is great. I notice it is a highly developed island, have alot of churches, almost all their parishes have church origins, I think. But the Cricket Kensington Oval and downtowm Bridgetown was best sites of all.

Probably one of the biggest difference is topography. Barbados is relatively flat causing it to be dry and hot. While here in SK we are mountainous and thus more likely to receive relief rainfall and sometimes a cooler rainshadow.

Becuz of this they have much more landuse available. The center of our island is unpopulated just a few farmers on the hillsides.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
evening 456 did you enjoy your little trip
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Member Since: July 24, 2005 Posts: 407 Comments: 19076


latest surface as of 2300
Member Since: July 15, 2006 Posts: 168 Comments: 53285
all so 94W is on its way to being the next TD
Member Since: May 21, 2006 Posts: 5091 Comments: 114653
CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION INVEST 93E



INITIAL TIME 18Z JUN 20



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 14.6 98.9 255./ 5.0

6 15.1 99.4 318./ 7.0

12 15.8 100.1 312./ 9.1

18 15.8 100.3 273./ 2.1

24 15.8 101.2 272./ 8.3

30 15.9 101.6 286./ 4.5

36 16.1 101.9 292./ 3.3

42 16.2 102.0 333./ 1.1

48 16.4 102.6 286./ 6.5

54 16.5 102.7 323./ 1.5

60 16.6 102.7 349./ 1.5

66 17.0 102.8 345./ 3.4

72 17.8 103.8 310./12.0

78 18.2 104.2 312./ 6.1

84 18.8 105.0 309./ 9.2

90 20.4 106.2 323./20.6

96 21.5 106.5 348./10.4

102 22.0 106.9 317./ 6.8

108 22.1 107.3 285./ 3.2

114 22.1 107.2 56./ .3

120 22.1 107.2 153./ .2



STORM DISSIPATED AT 120 HRS AT THE ABOVE PSN.
Member Since: July 15, 2006 Posts: 168 Comments: 53285
yeah i know petrol its gettin better organized as we type and it may well be a TD. by daylight tomorrow morning if things keep tighting up within the system
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188. KEEPEROFTHEGATE

KOTG, quite a few post back , I stated I thought 93E was TD already.
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Quoting PELLSPROG:
This CAN'T be right , anyone ????

Coral Ridge, Fort Lauderdale, FL
Visit Website, Add to My Blog, Set as Default Current Conditions, Historical Data & Charts 101.5 °F 69 °F 34% South at 4.0 mph
29.83 in 0.00 in / hr 109 °F 6 ft 0 sec ago Rapid Fire


Sure felt that hot today in Miami... A nice afternoon thunderstorm cooled things down.
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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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