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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It's cool. We all have fun trying to see what mother nature's going to throw at us each year. Sometimes, we're spot on. Other times, we're off by a long shot. But, all in all, it's fun.
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1343. Ossqss
Quoting HaboobsRsweet:


Point is forecasting is easy. I am also curious why a lot of Meteorologist over examine the facts and make it so much harder than it is.


That is where the truth is. You can't just use your eyes and be successful.

They are no different than a MD. They observe, analyze and confirm prior to making any judgement that directly affects those involved.

I am glad they do or we would all be in trouble.

Hence, the frustration this year with the NHC doing their job right. Just my take :)
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Quoting fire831rescue:


Actually, it was an attempt at a joke. A ribbing, if you will. I've been on here for years. Several bloggers can back me up on that. One thing that tends to happen is a lot of bickering back and forth and eventually feelings get hurt. I was more or less just poking fun. No offense meant by the comment.:D


My bad, didnt see the joke at first. No worries. Yes I am fairly new to the blog but have enjoyed reading it for quite awhile. Usually I never get offended so jab all you want. I will try to keep the bickering to a min :)
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I wouldn't rule out Andres becoming a cat 2 hurricane tomorrow.
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Quoting Stormchaser2007:
Nothing really left...I doubt anything will come of this as it moves NW until its landfall tomorrow night. I am aware of the diurnal phases.



Thats the mid level circulation, the low level circulation is SSE from that, has a very small burst of convection.. Tonight will be interesting, and for me cause there is a Severe Thunderstorm watch for my county in NE Florida.
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Quoting HaboobsRsweet:

I actually believe we agree with each other for starters and second off it is interesting that you consider myself a lower lifeform when you have no clue who I am or what my experience level is. I didn't realize voicing an opinion is a trend for someone of a "lower lifeform"


Actually, it was an attempt at a joke. A ribbing, if you will. I've been on here for years. Several bloggers can back me up on that. One thing that tends to happen is a lot of bickering back and forth and eventually feelings get hurt. I was more or less just poking fun. No offense meant by the comment.:D
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Quoting hurricane556:
huge convective burst on Andres


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Nothing really left...I doubt anything will come of this as it moves NW until its landfall tomorrow night. I am aware of the diurnal phases.

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Quoting fire831rescue:
StormW, you know better than to argue with the lower lifeforms that appear on the blog...

I actually believe we agree with each other for starters and second off it is interesting that you consider myself a lower lifeform when you have no clue who I am or what my experience level is. I didn't realize voicing an opinion is a trend for someone of a "lower lifeform"
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StormW, you know better than to argue with the lower lifeforms that appear on the blog...
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StormW you bring up a great point. I guess when you have sat in the chair for awhile it does get a lot easy to see the pattern and have an idea where things are going to move. The older the wiser haha.
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Quoting StormW:


Good point.

I understand everyone has their own process and I hope it works for them. It is just fun to see people turn blobs into hurricanes when there are so many factors saying it is never going to happen. You just have to look at what is right in front of you.
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Quoting CybrTeddy:
Atlantic Floater 1 now says 'invest'

Durinal Min is kicking the crap out of Possible-93L.
I think though it will rebound in the night during DMAX.


I agree. It might make Invest status but nothing more. It is going to push over Mexico. Hopefully some extreme southern parts of Texas get wet and some relief from this heat.
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Atlantic Floater 1 now says 'invest'

Durinal Min is kicking the crap out of Possible-93L.
I think though it will rebound in the night during DMAX.
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Quoting StormW:


Point?


Point is forecasting is easy. I am also curious why a lot of Meteorologist over examine the facts and make it so much harder than it is.
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Looks like midweek next week, the southern Gulf Coast will finally get some needed relief.
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Quoting Levi32:
SE temps:



And this is me =D



And he can see Russia from his house ... LOL
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Quoting hurricane2009:


Great here is a cookie


It wasnt meant to be oh look at me. I just took a beating because I said I wish everyone was a 100% or 0% forecaster because it does not good to say 30% or 70%. It is all or nothing. They also said you can not forecast more than 3 days. Why yes I agree on this for meso events but not the long wave pattern.
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huge convective burst on Andres
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1322. hahaguy
Quoting pottery:
Seems to me, that you all are suffering from exceeding hot temps, probably because my wife is there in Florida since Friday.
Just so happens, she is a Hot Caribbean Lady. That's why.
She is coming back tomorrow night. Hand on, it will cool after that.
hehehehheh


LOL
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1321. pottery
Seems to me, that you all are suffering from exceeding hot temps, probably because my wife is there in Florida since Friday.
Just so happens, she is a Hot Caribbean Lady. That's why.
She is coming back tomorrow night. Hang on, it will cool after that.
hehehehheh
Member Since: October 24, 2005 Posts: 0 Comments: 24925
Well, back on June 8th I told you all I was 100% sure nothing would form in the Gulf until at least 23 June and you all said there is no way you can say that. Well as I said then, that High is going no where anytime soon and it hasnt.

Now going into 23 June we may have an Invest. I still think it isnt going to be a TD, the high still has about 5 or 6 more days before it goes anywhere. Long term forecasting for synoptic patterns is easy. Just have to look at the facts.
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1318. 0741
my central air been running over time none top for 4 hour it soooo hot here in miami
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Member Since: July 8, 2005 Posts: 259 Comments: 24580
1316. KEEPEROFTHEGATE (Mod)

heat index 89.4
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting IKE:
State Highs:
Tallahassee 103%uFFFDF
Crestview 102%uFFFDF
Vero Beach 101%uFFFDF
Ocala 100%uFFFDF
Ft Lauderdale 100%uFFFDF


According to local TV weather you can add us in Pensacola with record at 100 for today.

edit: below added
Pensacola, Florida (Airport)
Updated: 58 min 52 sec ago
Scattered Clouds
100 %uFFFDF
Scattered Clouds
Humidity: 35%
Dew Point: 68 %uFFFDF
Wind: 12 mph from the NNW
Wind Gust: 16 mph
Pressure: 29.78 in (Steady)
Heat Index: 106 %uFFFDF
Visibility: 10.0 miles
UV: 4 out of 16
Clouds:
Scattered Clouds 7000 ft
(Above Ground Level)
Elevation: 118 ft

History & Almanac Hide
Max Temperature: Min Temperature:
Normal 90 F 73 F
Record 98 F (2006) 68 F (1965)
Yesterday 98 F 81 F
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1313. DDR
Quoting Levi32:


Well they're mild for us....and I bet there's more than a few Floridians who would love to trade places with me right about now =)

Hey! levi
what part of alaska are you from?
Do You have permafrost where you live?
Member Since: April 27, 2007 Posts: 14 Comments: 1730
Hi all

Just got home and noted the barometric pressure here is down to 1010.5 and still falling. This is the lowest surface pressure I have seen this year and perhaps an indicator that we are getting into the real start of the season. We have also had West and NW winds all day which are probably due to the tail end of the low off the East coast that is pushing a surge of cloud cover S over Cuba and into the NW Caribbean.

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1311. Levi32
Quoting futuremet:


lol 50s are not comfortable for me. I like it in the 80s


Well they're mild for us....and I bet there's more than a few Floridians who would love to trade places with me right about now =)
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Quoting Levi32:
SE temps:



And this is me =D



lol 50s are not comfortable for me. I like it in the 80s
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1308. Levi32
SE temps:



And this is me =D

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1307. IKE
State Highs:
Tallahassee 103°F
Crestview 102°F
Vero Beach 101°F
Ocala 100°F
Ft Lauderdale 100°F
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1306. Levi32
What the...?

east hills, Pensacola, Florida (PWS)
Updated: 1 sec ago
Scattered Clouds
112.4 °F
Scattered Clouds
Humidity: 34%
Dew Point: 77 °F
Wind: 2.9 mph from the North
Wind Gust: 2.9 mph
Pressure: 29.68 in (Steady)
Heat Index: 134 °F
Visibility: 10.0 miles
UV: 4 out of 16
Clouds:
Scattered Clouds 7000 ft
(Above Ground Level)
Elevation: 0 ft

APRSWXNET Pensacola FL US, Pensacola, Florida (PWS)
Updated: 8 sec ago
Scattered Clouds
104.0 °F
Scattered Clouds
Humidity: 33%
Dew Point: 69 °F
Wind: 0.0 mph
Wind Gust: 5.0 mph
Pressure: 29.77 in (Steady)
Heat Index: 112 °F
Visibility: 10.0 miles
UV: 4 out of 16
Clouds:
Scattered Clouds 7000 ft
(Above Ground Level)
Elevation: 87 ft
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1305. Levi32
Quoting futuremet:
The adjacent tropical cyclone is not really inhibiting the coalescence of the system in the BOC. The fact that it still seem to depend on diurnal fluxes, indicates that it is not something of much significance at the moment. At the pace it is moving, it has less than 24hrs to sufficiently consolidate to be considered a TS or even a TD.


If it wasn't for Andres more of the heat/energy would have made it north into the BOC. Since the other circulation became Andres it has hogged most of the heat and kept it south of Mexico, which has had a significant affect on the BOC system. It may not be close enough to be sheared by Andres' outflow, but its potential for development has been severely limited because of Andres' formation.
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Quoting DestinJeff:


doing that makes you cool though


When using jargon people are not familiar with, it is best not use abbreviations, because people won't know what the heck are talking about.
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1302. HadesGodWyvern (Mod)
** WTPH20 RPMM 221800 ***
T T T WARNING 01

At 18:00 PM UTC, 22nd of June.. Tropical Depression was estimated based on satellite and surface data at 10.8N 127.7E. Forecast to move west-northwest at 4 meters per second. Moderate to rough seas within 200 kilometer radius from center with estimated central pressure of 000 hPa (lol) and a maximum winds 15 meters per second

ALL SHIPS WITHIN DEPRESSION AREA ARE REQUESTED TO SEND THREE HOURLY WEATHER REPORTS TO WEATHER MANILA PD

WEATHER MANILA=

--
gotta love the pressure reading from them =P
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The adjacent tropical cyclone is not really inhibiting the coalescence of the system in the BOC. The fact that it still seem to depend on diurnal fluxes, indicates that it is not something of much significance at the moment. At the pace it is moving, it has less than 24hrs to sufficiently consolidate to be considered a TS or even a TD.
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Quoting Skyepony:
RECORD EVENT REPORT
NATIONAL WEATHER SERVICE MELBOURNE
430 PM EDT MON JUN 22 2009

...ALL TIME RECORD HIGH TEMPERATURE SET AT VERO BEACH TODAY...

A RECORD HIGH TEMPERATURE OF 101 DEGREES WAS SET AT VERO BEACH
TODAY. THIS BREAKS THE OLD RECORD OF 95 SET IN 2007. THIS IS ALSO
THE HOTTEST TEMPERATURE ON RECORD FOR VERO BEACH. THE OLD RECORD WAS
100 DEGREES SET ON JUNE 27, 1950.


$$
MRT


Melbourne's high was broken, Daytona's tied. I don't like seeing the high records from that last strong El Niño we had fall. That was the El Niño when FL burnt down.




All Time Records are 102 in Orlando, Daytona and Melbourne. Goes to show you how rare it is to get this hot.
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1299. IKE
I lived in Springfield...we came through okay. PC beach was a big-time mess and that motel that was on the west-end of PCB, near Phillip's Inlet, got it's ass kicked w/a storm surge. Incredible sight I'll never forget.
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1298. HadesGodWyvern (Mod)
The Philippines names 04W - Feria
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Quoting atmoaggie:


Uhhhhgh. I gladly would take winter...


I hear ya on that, its 104 here in downtown Kansas city, down right baking with 35% humidty. I am staying inside all day. A bit uncommon to see temps this high in June.
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1295. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #1
TROPICAL DEPRESSION
3:00 AM JST June 23 2009
===================================

At 18:00 PM UTC, Tropical Depression (1002 hPa) located at 10.9N 127.6E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving west at 12 knots.

Dvorak Intensity: T2.0

Forecast and Intensity
=====================
24 HRS: 13.4N 123.5E - 35 knots (Tropical Storm/CAT 1)
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1294. GatorWX
Quoting KEEPEROFTHEGATE:
its called the day effect went the sun goes down the storm will ramp up
wait watch see


I know that, but shear seems to have increased since last night. Lowest values are very near the coast, and increase further out. Andres is under about 15 kts according to cimss, or 10-20 I guess.
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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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