Dust forecast for the 2009 Atlantic hurricane season

By: Dr. Jeff Masters , 20. kesäkuuta 2009 klo 18:58 (GMT)

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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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1744. Unfriendly
23. kesäkuuta 2009 klo 16:15 (GMT)
Quoting CycloneOz:
The XtremeTeam from XtremeHurricanes.com will not be hunting Andres.

Why? (besides the time crunch of getting down there...)

Would you bring $10K worth of equipment into Mexico these days? ;)


Isnt the W coast of Mexico closer to you then florida anyway? Though can't say I blame you for the monetary (and safety) risk... not exactly stable down there.
Member Since: 21.07.2008 Posts: 0 Comments: 291
1743. AussieStorm
23. kesäkuuta 2009 klo 16:09 (GMT)
Quoting hurricane2009:


If they declared every defined surface circulation there would be over 200 invests every season, convection is very disorganized and has shown no signs of it getting better organized. Also due to the fact it wont have much more time over water, it is kind of pointless.

Look at this. Link
Member Since: 30.09.2007 Posts: 9 Comments: 15742
1742. IKE
23. kesäkuuta 2009 klo 16:09 (GMT)
NEW BLOG!
Member Since: 9.06.2005 Posts: 23 Comments: 37858
1741. Fla55Native
23. kesäkuuta 2009 klo 16:05 (GMT)
Quoting AussieStorm:

Link to that image Link


Thanks. Nice loop.
Member Since: 25.08.2008 Posts: 0 Comments: 63
1739. AussieStorm
23. kesäkuuta 2009 klo 16:01 (GMT)
132 Hrs time


Look whats coming off the coast of Africa
Member Since: 30.09.2007 Posts: 9 Comments: 15742
1738. AussieStorm
23. kesäkuuta 2009 klo 15:58 (GMT)
Quoting Fla55Native:


Just wondering where you found that particularimage. I'm out here on Bee Ridge Rd. 2 miles from I-75, due east of Siesta Key.

Link to that image Link
Member Since: 30.09.2007 Posts: 9 Comments: 15742
1737. CycloneOz
23. kesäkuuta 2009 klo 15:54 (GMT)
The XtremeTeam from XtremeHurricanes.com will not be hunting Andres.

Why? (besides the time crunch of getting down there...)

Would you bring $10K worth of equipment into Mexico these days? ;)
Member Since: 26.08.2006 Posts: 10 Comments: 3420
1736. Fla55Native
23. kesäkuuta 2009 klo 15:52 (GMT)
Quoting stillwaiting:
still alot of UL energy up the road for the FL area,as the area highlighted moves over the region,a severe thunderstorm watch is no doubt warranted for this afternoon:


Just wondering where you found that particularimage. I'm out here on Bee Ridge Rd. 2 miles from I-75, due east of Siesta Key.
Member Since: 25.08.2008 Posts: 0 Comments: 63
1735. stillwaiting
23. kesäkuuta 2009 klo 15:51 (GMT)
the area in the BOC should be a invest,it has a defined surface circulation,IMO
Member Since: 5.10.2007 Posts: 20 Comments: 4970
1734. GOLSUTIGERS
23. kesäkuuta 2009 klo 15:49 (GMT)
Send the blob to Baton Rouge as long as it is a rain soaker. We have only had 0.59 inches of rain this month. We need it.
Member Since: 25.06.2008 Posts: 0 Comments: 47
1733. Skyepony (Mod)
23. kesäkuuta 2009 klo 15:48 (GMT)
There was a pretty pompt switch of winds fron ESE to WSW around 21.650N 96.617W at flight level (~27,000ft). They were a little variable for a few minutes after even saw a NW wind in there. Highest surface wind so far via SFMR 28 knots(~ 32.2 mph) just west of center of the last blow up at 21.450N 96.783W.
Member Since: 10.08.2005 Posts: 156 Comments: 36062
1732. AussieStorm
23. kesäkuuta 2009 klo 15:44 (GMT)

TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT TUE JUN 23 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A TROUGH OF LOW PRESSURE IN THE SOUTHWESTERN GULF OF MEXICO
CONTINUES TO PRODUCE DISORGANIZED SHOWERS AND THUNDERSTORMS. THIS
ACTIVITY IS EXPECTED TO MOVE SLOWLY NORTHWESTWARD...BRINGING
LOCALLY HEAVY RAINFALL TO PORTIONS OF EAST-CENTRAL AND NORTHEASTERN
MEXICO OVER THE NEXT COUPLE OF DAYS. SIGNIFICANT DEVELOPMENT IS NOT
EXPECTED...WITH A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER FRANKLIN
Member Since: 30.09.2007 Posts: 9 Comments: 15742
1731. AussieStorm
23. kesäkuuta 2009 klo 15:42 (GMT)


Severe Weather Bulletin Number FOUR
Tropical Cyclone Warning: Tropical Storm "FERIA" {NANGKA}
Issued at 10:45 p.m., Tuesday, 23 June 2009

Tropical Storm "FERIA" has crossed Northern Samar and is now in the vicinity of Masbate.
Location of Center:
(as of 10:00 p.m.) in the vicinity of Masbate

Coordinates: 12.5°N, 123.6°E

Strength: Maximum sustained winds of 75 kph near the center and
Gustiness of up to 90 kph

Movement: West Northwest at 22 kph

Forecast Positions/Outlook:
Wednesday evening:
90 kms West of Iba, Zambales
Thursday evening:
290 kms Northwest of Laoag City
Friday evening:
420 kms North Northwest of Basco, Batanes


Member Since: 30.09.2007 Posts: 9 Comments: 15742
1730. stillwaiting
23. kesäkuuta 2009 klo 15:40 (GMT)
still alot of UL energy up the road for the FL area,as the area highlighted moves over the region,a severe thunderstorm watch is no doubt warranted for this afternoon:
Member Since: 5.10.2007 Posts: 20 Comments: 4970
1729. Ossqss
23. kesäkuuta 2009 klo 15:36 (GMT)
12Z

Member Since: 12.06.2005 Posts: 6 Comments: 8183
1728. CaneWarning
23. kesäkuuta 2009 klo 15:36 (GMT)
Quoting TheCaneWhisperer:


I can't remember the last time we we're under a severe t-storm watch in these parts, it's got my attention. We get severe thunderstorms everyday?



Yeah, they don't issue watches for Florida too often so its interesting to see.
Member Since: 26.04.2009 Posts: 3 Comments: 3667
1727. TheCaneWhisperer
23. kesäkuuta 2009 klo 15:34 (GMT)
Quoting CaneWarning:
Well storms are starting to form. We'll see if they become severe.


I can't remember the last time we we're under a severe t-storm watch in these parts, it's got my attention. We get severe thunderstorms everyday?
1726. Ossqss
23. kesäkuuta 2009 klo 15:34 (GMT)
Perhaps related to the watch. Mornin

Member Since: 12.06.2005 Posts: 6 Comments: 8183
1725. CaneWarning
23. kesäkuuta 2009 klo 15:33 (GMT)
I'll take a severe storm if it cools us off. My luck, the power will go out and we'll still be hot!
Member Since: 26.04.2009 Posts: 3 Comments: 3667
1724. RitaEvac
23. kesäkuuta 2009 klo 15:29 (GMT)
Quoting txalwaysprepared:


I'm in Clear Lake... not a drop


Thought you moved to Katy?
Member Since: 14.07.2008 Posts: 1 Comments: 9625
1723. AussieStorm
23. kesäkuuta 2009 klo 15:28 (GMT)
Quoting CaneWarning:
Well storms are starting to form. We'll see if they become severe.

Member Since: 30.09.2007 Posts: 9 Comments: 15742
1722. jeffs713
23. kesäkuuta 2009 klo 15:28 (GMT)
Quoting Timstorm:
To Txalwaysprepared:

Houston did get rain yesterday evening. A good steamy soaking downtown and points northwest. First good dousing in a month.

pics or it didn't happen.

The entire Houston area needs 3-4 days of a steady rain to break the drought. A single storm won't do it, since a lot of that runs off, and doesn't get absorbed.

That said.... I'm not expecting steady rain until October-ish.
Member Since: 3.08.2008 Posts: 16 Comments: 5792
1721. txalwaysprepared
23. kesäkuuta 2009 klo 15:29 (GMT)
Quoting Timstorm:
To Txalwaysprepared:

Houston did get rain yesterday evening. A good steamy soaking downtown and points northwest. First good dousing in a month.


I'm in Clear Lake... not a drop
Member Since: 18.08.2007 Posts: 0 Comments: 1642
1720. Skyepony (Mod)
23. kesäkuuta 2009 klo 15:25 (GMT)
Doesn't look like recon is going to decend in the BOC blob..but they have the SFMR on (which alotta times we don't see in route)..so we get surface winds during the flyby. Smaller dying blob bit on the NE side, 23.450N 95.150W ~ 31mph at the surface.
Member Since: 10.08.2005 Posts: 156 Comments: 36062
1718. CaneWarning
23. kesäkuuta 2009 klo 15:24 (GMT)
Well storms are starting to form. We'll see if they become severe.
Member Since: 26.04.2009 Posts: 3 Comments: 3667
1716. Timstorm
23. kesäkuuta 2009 klo 15:22 (GMT)
To Txalwaysprepared:

Houston did get rain yesterday evening. A good steamy soaking downtown and points northwest. First good dousing in a month.
Member Since: 26.07.2007 Posts: 0 Comments: 4
1715. txalwaysprepared
23. kesäkuuta 2009 klo 15:18 (GMT)
well all I'm done lurking for today.. sorry not being chatty this year... just watching.

Have a good Tuesday!
Member Since: 18.08.2007 Posts: 0 Comments: 1642
1713. CaneWarning
23. kesäkuuta 2009 klo 15:16 (GMT)
Quoting weathersp:


A Severe Thunderstorm Watch is issued when weather conditions are favorable for the development of severe thunderstorms, not nessarilly thunderstom presesnt. A watch must not be confused with a severe thunderstorm warning.


I know, but I do not see conditions being all that favorable at the moment.
Member Since: 26.04.2009 Posts: 3 Comments: 3667
1709. stillwaiting
23. kesäkuuta 2009 klo 15:11 (GMT)
Quoting CaneWarning:
I still can't figure out why Tampa is under a severe t-storm watch. There are no storms anywhere near us.



uno memento!!!!,they'll start firing near I-75 to the north of the bay and move SSE between 25-40mph,as the line that forms moves slowly SW....give it a hour or 2 things w/be very active in our area,IMO(I'm down on siesta key)
Member Since: 5.10.2007 Posts: 20 Comments: 4970
1708. DaytonaBeachWatcher
23. kesäkuuta 2009 klo 15:11 (GMT)
Quoting hurricane2009:


lol 95% of the counties that were under the Watch saw absolutely nothing from the time they issued it to the time it expired, I would say that is pretty off then.



I wasnt arguing the point, i was asking, Really? and then providing my own info. I dont know for sure what was forcast and i sure dont know for sure what occurred anywhere but here.
Member Since: 29.06.2007 Posts: 0 Comments: 1135
1707. jeffs713
23. kesäkuuta 2009 klo 15:10 (GMT)
Quoting hurricane2009:


lol 95% of the counties that were under the Watch saw absolutely nothing from the time they issued it to the time it expired, I would say that is pretty off then.



All a severe thunderstorm watch does is indicate that conditions are right for storms to form. It does not indicate that a severe thunderstorm WILL form, nor does it indicate that your area will get rain.

Considering how much that we don't know about what causes a storm to be severe vs. just strong, I would think that a watch is warranted. Nothing weather-wise can be predicted with 100% certainty, and that includes severe thunderstorms.

Since you seem to be pretty perturbed by the lack of severe storms... may I ask what difference it makes whether the NWS called a severe thunderstorm watch or not, since a storm didn't impact you? Wouldn't you rather be advised to be wary, since conditions are ripe, or would you rather to suddenly have a warning issued when a storm does pop?
Member Since: 3.08.2008 Posts: 16 Comments: 5792
1706. weathersp
23. kesäkuuta 2009 klo 15:08 (GMT)
Quoting CaneWarning:
I still can't figure out why Tampa is under a severe t-storm watch. There are no storms anywhere near us.


A Severe Thunderstorm Watch is issued when weather conditions are favorable for the development of severe thunderstorms, not nessarilly thunderstom presesnt. A watch must not be confused with a severe thunderstorm warning.
Member Since: 14.01.2007 Posts: 17 Comments: 4140
1703. sporteguy03
23. kesäkuuta 2009 klo 15:03 (GMT)
Not sure how severe weather can be well deserved unless you meant the rainfall and cloud cover.
Member Since: 7.07.2005 Posts: 0 Comments: 5120
1702. DaytonaBeachWatcher
23. kesäkuuta 2009 klo 15:03 (GMT)
Quoting hurricane2009:


Well they were dead wrong last night about the watch they put up for east central florida. Guess we will see how it goes today.
Really? cuz we had severe thunderstorms here last night between 9:30 and 12 midnight.
Member Since: 29.06.2007 Posts: 0 Comments: 1135
1701. nrtiwlnvragn
23. kesäkuuta 2009 klo 15:03 (GMT)
Quoting CaneWarning:
I still can't figure out why Tampa is under a severe t-storm watch. There are no storms anywhere near us.


SEVERE THUNDERSTORM WATCH NUMBER 495
Member Since: 23.09.2005 Posts: 13 Comments: 10458
1699. jeffs713
23. kesäkuuta 2009 klo 15:01 (GMT)
Quoting txalwaysprepared:
::sigh::

will Houston ever get some rain? ( I know, I know, I shouldn't ask...)

Be careful what you ask for... Remember April.
Member Since: 3.08.2008 Posts: 16 Comments: 5792
1696. Patrap
23. kesäkuuta 2009 klo 14:56 (GMT)
1695. CaneWarning
23. kesäkuuta 2009 klo 14:56 (GMT)
The University of Tampa, Tampa, Florida (PWS)
Updated: 0 sec ago
93.7 °F
Scattered Clouds
Humidity: 67%
Dew Point: 81 °F
Wind: 12.0 mphfrom the NNW
Wind Gust: 20.0 mph
Pressure: 29.72 in (Falling)
Heat Index: 115 °F
Visibility: 10.0 miles
UV: 7 out of 16

The heat index is already 115 and it isn't even 11 AM!

Member Since: 26.04.2009 Posts: 3 Comments: 3667
1694. txalwaysprepared
23. kesäkuuta 2009 klo 14:56 (GMT)
::sigh::

will Houston ever get some rain? ( I know, I know, I shouldn't ask...)
Member Since: 18.08.2007 Posts: 0 Comments: 1642

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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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