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: 1094 - 1044

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

1094. IKE
That Crestview,FL. temp I posted of 101 is a record for the date.
Member Since: Posts: Comments:
1092. IKE
Quoting Levi32:
I feel so sorry for you guys....



Try going to town in a car with no AC working.

What's real fun is getting in the car AFTER stopping somewhere and the car has been on that hot asphalt.....it must be 120-130 in my car....

Member Since: Posts: Comments:
Quoting Levi32:


You're absolutely right though :)


YAY! I learneded something! ;)
Member Since: Posts: Comments:
1089. IKE
20 miles to my west>>>>

"Crestview, Florida (Airport)
Updated: 31 min 43 sec ago
Partly Cloudy
101 °F

Partly Cloudy
Humidity: 39%
Dew Point: 72 °F
Wind: 9 mph from the NNW
Pressure: 29.81 in (Falling)
Heat Index: 111 °F
Visibility: 8.0 miles
UV: 12 out of 16
Clouds:
Few 6000 ft
(Above Ground Level)
Elevation: 210 ft"
Member Since: Posts: Comments:
1088. Levi32
I feel so sorry for you guys....

Member Since: November 24, 2005 Posts: 635 Comments: 26647
1086. NEwxguy
I can't get over how many of you are breaking the triple digits,an amazing heatwave for so early in the season
Member Since: Posts: Comments:
WU is stating the heat index is now 118 by my work in zip 34996.
Member Since: Posts: Comments:
1084. NRAamy
My Local Weather:
John Wayne-Orange County, California
71 °F
Clear
Member Since: Posts: Comments:
1081. Levi32
Quoting extreme236:
H2009, looks like one trying to now:



Definitely forming an eye now. We'll see if the structure holds.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
1080. IKE
I've got 100.0 at my house......
Member Since: Posts: Comments:
1079. Levi32
Quoting jeffs713:

One of the people with the links can probably post more detail, but from what I understand right now, El Nino is still in its infant stages. It isn't fully established, but it is trending towards getting there. If it keeps on the current trend, it projects to be a moderate El Nino, but it likely won't impact the Atlantic hurricane season until the latter half of the season, if at all. There has been some lag in the past between El Nino forming and the ATL basin feeling it, and other years have not had much lag at all. I think the lag part depends mostly upon whether the atmosphere is reacting to the ocean, or vice versa. If the atmosphere leads, there isn't much lag. If the ocean leads, there is lag.

[edit: Levi beat me to the post. I wrote too much. hehe]


You're absolutely right though :)
Member Since: November 24, 2005 Posts: 635 Comments: 26647
H2009, looks like one trying to now:

Member Since: August 2, 2007 Posts: 19 Comments: 19234
1077. Levi32
Quoting hurricane2009:


So could it be summarized that the MJO could have a huge part in determing overall activity for this hurricane season?


I think it usually does. In El Nino the MJO naturally gets stuck in this position with upward motion focused over the east Pacific which contributes to the active seasons they have there during El Nino events. Once the pattern gets better-established we should see more downward motion develop over the tropical Atlantic.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
1076. IKE
My hometown....ah....nice & cool......

"WZEP AM 1460 DeFuniak Springs, FL, DeFuniak Springs, Florida (PWS)
Updated: 22 min 36 sec ago
Partly Cloudy
97.3 °F

Partly Cloudy
Humidity: 47%
Dew Point: 74 °F
Wind: 5.0 mph from the WNW
Wind Gust: 12.0 mph
Pressure: 29.75 in (Falling)
Heat Index: 108 °F
Visibility: 8.0 miles
UV: 12 out of 16
Clouds:
Few 6000 ft
(Above Ground Level)
Elevation: 174 ft"
Member Since: Posts: Comments:
We're still in a warm neutral baised btw guys, not an El Nino although we're getting closer to it.
Member Since: Posts: Comments:
The University of Tampa, Tampa, Florida (PWS)
Updated: 1 sec ago
96.2 °F
Clear
Humidity: 55%
Dew Point: 77 °F
Wind: 10.0 mphfrom the West
Wind Gust: 25.0 mph
Pressure: 29.74 in (Falling)
Heat Index: 112 °F


I hate Florida.
Member Since: Posts: Comments:
Quoting Chicklit:
2009 Hurricane Season
Act I
Begins with intense heating of waters...

I'd like to hear more about how strong the proposed El Nino will be.
Can you explain its current status/development in the style of "El Nino for Dummies?"

Thanks.

One of the people with the links can probably post more detail, but from what I understand right now, El Nino is still in its infant stages. It isn't fully established, but it is trending towards getting there. If it keeps on the current trend, it projects to be a moderate El Nino, but it likely won't impact the Atlantic hurricane season until the latter half of the season, if at all. There has been some lag in the past between El Nino forming and the ATL basin feeling it, and other years have not had much lag at all. I think the lag part depends mostly upon whether the atmosphere is reacting to the ocean, or vice versa. If the atmosphere leads, there isn't much lag. If the ocean leads, there is lag.

[edit: Levi beat me to the post. I wrote too much. hehe]
Member Since: Posts: Comments:
Thanks vortfix!
Member Since: Posts: Comments:
Heat index's are busting through the 105 to 110 forecast.

2 miles in from the Ocean.

Pennock Ln., Jupiter, Florida (PWS)
Updated: 1 sec ago
Scattered Clouds
98.0 °F
Scattered Clouds
Humidity: 53%
Dew Point: 78 °F
Wind: 0.7 mph from the WNW
Wind Gust: 4.6 mph
Pressure: 29.72 in (Falling)
Heat Index: 115 °F
Member Since: Posts: Comments:
1058, you are 100% correct the humidity is really low for us. I'm looking at the sky right now and see absolutely nothing that looks like rain is developing, scattered clouds and that's it. I think if & when they do pop up they'll likely be a few severe ones... but we'll see
Member Since: Posts: Comments:
The only interesting thing here in Charleston, Sizzolina, is exceptionally high Spring tides causing some flooding...
Member Since: Posts: Comments:
1065. Levi32
Quoting Chicklit:
2009 Hurricane Season
Act I
Begins with intense heating of waters...

I'd like to hear more about how strong the proposed El Nino will be.
Can you explain its current status/development in the style of "El Nino for Dummies?"

Thanks.


It's a reactive El Nino. This is how I explained it to someone a week ago:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The ENSO is an atmospheric-oceanic relationship. A reactive El Nino means that the ocean is reacting to what the atmosphere is doing. A perfect demonstration of this is happening right now. The MJO is starting to bring another round of downward motion into the West Pacific. All that sinking air spreads outward at the ocean surface, creating high pressure.

Similarly, the MJO upward motion pulse is now over the east Pacific, and all that rising air is creating low pressure at the surface. Since air naturally flows from high to low pressure, you get increased westerlies across the equatorial Pacific. This also lowers the SOI.

This is the classic atmospheric signature of El Nino, and the ocean reacts because the westerlies push warm water eastward usually in the form of Kelvin Waves and pile it up in the central/eastern Equatorial Pacific.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As for how strong it will get, that's the unpredictable part, but it will probably be a moderate event. I hope I made at least some sense lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting CybrTeddy:
Good view of both systems.


If it wasn't for the land mass beween them, someone on here would be talking about the Fujiwara effect already.....Lol
Member Since: Posts: Comments:
Wow ...101.1 F
Heat index ...119 F

Pensacola - http://www.wunderground.com/cgi-bin/findweather/getForecast?query=32505
Member Since: Posts: Comments:
2009 Hurricane Season
Act I
Begins with intense heating of waters...

I'd like to hear more about how strong the proposed El Nino will be.
Can you explain its current status/development in the style of "El Nino for Dummies?"

Thanks.
Member Since: July 11, 2006 Posts: 14 Comments: 11328
Quoting 954FtLCane:
I have never seen it this hot down here before & I'm a native so I had to share

Coral Ridge, Fort Lauderdale, Florida (PWS)
Updated: 3:07 PM EDT on June 22, 2009
Scattered Clouds
101.1 °F
Scattered Clouds
Humidity: 33%
Dew Point: 67 °F
Wind: 7.6 mph from the North
Wind Gust: 10.1 mph
Pressure: 29.71 in (Falling)
Heat Index: 106 °F
Visibility: 9.0 miles
UV: 11 out of 16
Clouds:
Scattered Clouds 4200 ft
(Above Ground Level)
Elevation: 6 ft

Egad. Be happy the humidity is only 33%.
Member Since: Posts: Comments:
I have never seen it this hot down here before & I'm a native so I had to share

Coral Ridge, Fort Lauderdale, Florida (PWS)
Updated: 3:07 PM EDT on June 22, 2009
Scattered Clouds
101.1 °F
Scattered Clouds
Humidity: 33%
Dew Point: 67 °F
Wind: 7.6 mph from the North
Wind Gust: 10.1 mph
Pressure: 29.71 in (Falling)
Heat Index: 106 °F
Visibility: 9.0 miles
UV: 11 out of 16
Clouds:
Scattered Clouds 4200 ft
(Above Ground Level)
Elevation: 6 ft
Member Since: Posts: Comments:
1055. Levi32
Quoting hurricane2009:


ok close enough lol, I see what you mean about that wrapping around, could see an eye pop out later tonight


Lol I hate developing CDOs....their waxing and waning of convective mass makes it hard to determine the real motion.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting Levi32:


As I understand it it's primarily based on the depth of the warm water. If you compare the TCHP map with the 26c isotherm-depth map, you can see they usually match up pretty well.

Per Link,
"The tropical cyclone heat potential (hereafter TCHP), is defined as a measure of the integrated vertical temperature from the sea surface to the depth of the 26°C isotherm. "

To translate, it is basically a function of how deep the 26C isotherm is (isotherm = boundary layer within water, generally by temperature), in combination with SST, and how quickly it cools going down. You could have a equally deep 26C isotherm and the same SST in two areas, but one may have more TCHP because the warmth goes deeper (the 28C isotherm is deeper in the one with higher TCHP, for example).

Generally, the warmer the water, and the higher the SST, the higher the TCHP goes. TCHP values above 80-100 kJ/cm^2 mean the water is ripe for rapid intensification, IF all other atmospheric factors line up. (those areas are generally highlighted in a black line, with red and pink inside)

The NOAA TCHP page is an excellent resource for learning more, and seeing some extreme examples with Katrina and Rita. You can also pull up some historical maps for further info.
Member Since: Posts: Comments:
1052. IKE
Quoting K8eCane:



and what you said sounded like an ignorant "ninny ninny boo boo" I hear that crap too much on here
its ignorant
nobody but YOU said anything at all about a low off the carolinas


You're gonna get banned talking like that.
Member Since: Posts: Comments:
I read earlier on the blog that Florida was going to get some nasty storms this afternoon.....I'm lookin at radar and there is nothing (so far)..I know they can pop up but can anyone post if they updated that? I don't know where to go to get that information you are posting. I usually receive emails with it but I don't know what happened because I do not get them anymore...

Thanks to anyone who can helop me with this..

Member Since: Posts: Comments:
Good view of both systems.
Member Since: Posts: Comments:
1048. Levi32
Quoting hurricane2009:
Is it me or did Andres take a jog back to the south?


6-hour motion appears to be near stationary or a very slow drift towards the WNW.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Incredible stuff for south florida standards...

Member Since: Posts: Comments:
Quoting Chicklit:

And which Carolina are you talking about?!
LMAO that would be South Pressolina....
Member Since: Posts: Comments:
1044. Levi32
Quoting hurricane2009:
Levi is the heat content the ability of a body of water to hold its temperature?


As I understand it it's primarily based on the depth of the warm water. If you compare the TCHP map with the 26c isotherm-depth map, you can see they usually match up pretty well.
Member Since: November 24, 2005 Posts: 635 Comments: 26647

Viewing: 1094 - 1044

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

Partly Cloudy
72 °F
Partly Cloudy