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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::sigh::

will Houston ever get some rain? ( I know, I know, I shouldn't ask...)
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I still can't figure out why Tampa is under a severe t-storm watch. There are no storms anywhere near us.
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1692. NRAamy
My Local Weather:
John Wayne-Orange County, California
64 °F
Overcast
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I think we'll see an invest in the BOC by this afternoon. It seems to at least marginably favorable for slow development.
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Quoting Skyepony:
I wonder if we will see recon decend through the BOC blob or just fly over.


Takes more fuel to fly at lower altitudes then climb back up... They would probably have to fly one pass into Andres then fly back.

Hey at least we get some HDOB Upper Air data for the models.

They could drop a dropsonde too.
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1689. KEEPEROFTHEGATE (Mod)
there making a quick check on aoi maybe wave hello visit andres then drop by for one more look and see on the way back
Member Since: July 15, 2006 Posts: 174 Comments: 54372
1688. Patrap
Current Conditions

Uptown, New Orleans, Louisiana (PWS)
Updated: 1 sec ago
Partly Cloudy
90.7 °F
Partly Cloudy


Heat Advisory
Heat Advisory

Statement as of 5:03 AM CDT on June 23, 2009





Area forecast discussion
National Weather Service New Orleans la
821 am CDT Tuesday Jun 23 2009



The 500 mb high will continue to become centered farther west
Wednesday...but the ridge axis will continue to extend west into
portions of the lower Mississippi Valley and western Gulf Coast.
This will maintain the hot temperatures at the surface and warm
air in the middle levels. The only place that might see some isolated
late afternoon convection is near the seabreeze and lake breeze
boundaries south of Lake Pontchartrain and on the Mississippi
coast with some help from one or two weak disturbances rotating
around the upper high. Any thicker or higher coverage convective
clouds will be too late in the day to cut into the high
temperatures. Have extended the heat advisory through 7 PM
Wednesday.
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1687. KEEPEROFTHEGATE (Mod)
i know sky we will see what they do when they get there
Member Since: July 15, 2006 Posts: 174 Comments: 54372
1684. Skyepony (Mod)
Keeper~ That's the altitute they are going to fly Andres. Right now they are approaching BOC blob & at ~27,500ft.
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Quoting CaneWarning:
Tampa is under a severe t-storm watch. I'm just not sure where the storms will come from right now. The storms already out there will go well to our south.
They should start to develop right along 75 around 12pm
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1682. Skyepony (Mod)
I like to call them NOAA declared invests since NOAA is calling it an invest.

22/1745 UTC 21.1N 95.9W T1.0/1.0 INVEST
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1681. KEEPEROFTHEGATE (Mod)
Quoting Skyepony:
I wonder if we will see recon decend through the BOC blob or just fly over.


SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 23/1100Z TO 24/1100Z JUNE 2009
TCPOD NUMBER.....09-025

II. PACIFIC REQUIREMENTS
1. TROPICAL STORM ANDRES
FLIGHT ONE -- TEAL 70
A. 23/1800Z
B. AFXXX 0102E ANDRES
C. 23/1300Z
D. 18.4N 104.0W
E. 23/1700Z TO 23/2100Z
F. SFC TO 10,000 FT

VALID 24/1100Z TO 25/1100Z JUNE 2009
TCPOD NUMBER.....09-026

II. PACIFIC REQUIREMENTS
1. TROPICAL STORM ANDRES
FLIGHT ONE -- TEAL 70
A. 24/1800Z
B. AFXXX 0202E ANDRES
C. 24/1245Z
D. 21.5N 107.8W
E. 24/1700Z TO 24/2100Z
F. SFC TO 10,000 FT
look at f for anwser
Member Since: July 15, 2006 Posts: 174 Comments: 54372
Quoting hurricane2009:
The ssd floater has said Invest since yesterday afternoon, the ssd has done that before without an invest officially classified

No Invest has officially been classified for that area.


Arg, and they really had my hopes up, too.
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1679. Patrap
Looks like "Link season" will be on the increase as per the Seasonal Up-tick in activity.

We turn towards the meat of the season soon.
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1678. Skyepony (Mod)
I wonder if we will see recon decend through the BOC blob or just fly over.
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Hey Pat... Seems like your favorites list must have 1000's of links LOL. I appreciate all of the ones you throw out there for us.
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1676. Patrap
Texas was A fun 3 Days.

And twas good to get back and see the recovery continuing there.



Pocahontas
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1675. KEEPEROFTHEGATE (Mod)
welcome back pat how was texas if i may ask
Member Since: July 15, 2006 Posts: 174 Comments: 54372
1674. KEEPEROFTHEGATE (Mod)
its a AOI in the boc
no invest at this time
Member Since: July 15, 2006 Posts: 174 Comments: 54372
1673. Patrap

GOM 84 Hour Wind Forecast Model
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1672. Patrap
ESL GOM IR Loop

NexSat GOM Vis Loop
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Nothing on navy site
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We got us an invest:



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
NNNN
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Quoting OnTheFlats:
I'm in Deerfield as well and those strikes were intense to say the least. Where are you in Deerfield Beach? I'm in The Cove area on the border of Lighthouse Point. Seems to be settling down now and ooks like a good window to get out of the house and head to work.


Im on the beach on A1A in Deerfield; that lightning associated with the line of storms that moved through around 8AM was the worst lightning I've seen down here in quite some time---talking 20-30 strikes a minute at one point

I wonder how unstable the atmosphere is here in south FL and if another round of storms will fire up later today with the daytime heating.
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Recon is on their way to Andres Google Earth view
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i love you too
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1662. NEwxguy
What I love about this blog is you ask a question and you get a ton of great answers and usually in terms us amateurs can understand.Good job to all of you.
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i think we have El Nino

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1660. JRRP
strong winds from the Wave near antilles
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although the sst's in the west pac and epac have warmed cosiderably hinting of a el nino the atmosphere in this region has not responded to the at possibility
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1658. KEEPEROFTHEGATE (Mod)
Quoting lamanzanilla:
Experiencing the calm before the
storm here on the mid-Pacific coast this morning. Andres is still at tropical storm level, slowly churning up the coast toward us. We're at approx. 19N/105W so watching very closely. Nerve-wracking, to say the least!




1249 UTC TUE JUN 23 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



TROPICAL CYCLONE ANDRES (EP022009) 20090623 1200 UTC



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

090623 1200 090624 0000 090624 1200 090625 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 17.8N 104.0W 19.3N 104.6W 20.4N 105.3W 21.0N 106.4W

BAMD 17.8N 104.0W 18.8N 105.1W 19.5N 106.5W 20.2N 108.2W

BAMM 17.8N 104.0W 19.4N 105.1W 20.5N 106.4W 21.3N 108.1W

LBAR 17.8N 104.0W 19.3N 105.2W 20.8N 106.6W 22.1N 108.2W

SHIP 60KTS 62KTS 60KTS 56KTS

DSHP 60KTS 62KTS 60KTS 56KTS



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

090625 1200 090626 1200 090627 1200 090628 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 21.5N 107.6W 22.5N 109.8W 23.4N 112.1W 24.1N 115.4W

BAMD 21.0N 109.9W 22.9N 113.3W 25.0N 116.7W 27.8N 119.7W

BAMM 22.1N 110.1W 24.0N 113.7W 25.8N 117.4W 28.0N 121.1W

LBAR 23.2N 110.1W 25.6N 113.1W 28.4N 114.9W 30.4N 115.0W

SHIP 48KTS 25KTS 0KTS 0KTS

DSHP 48KTS 25KTS 0KTS 0KTS



...INITIAL CONDITIONS...

LATCUR = 17.8N LONCUR = 104.0W DIRCUR = 315DEG SPDCUR = 9KT

LATM12 = 16.7N LONM12 = 102.7W DIRM12 = 319DEG SPDM12 = 7KT

LATM24 = 15.8N LONM24 = 101.9W

WNDCUR = 60KT RMAXWD = 25NM WNDM12 = 55KT

CENPRS = 990MB OUTPRS = 1004MB OUTRAD = 120NM SDEPTH = D

RD34NE = 60NM RD34SE = 60NM RD34SW = 40NM RD34NW = 40NM


ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL STORM ANDRES 02E



INITIAL TIME 6Z JUN 23



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 17.2 103.3 320./ 6.0

6 18.2 104.2 317./12.9

12 19.5 105.5 317./17.3

18 21.4 106.1 342./20.4

24 22.3 106.9 316./11.2

30 22.6 107.5 301./ 6.1

36 24.3 108.6 325./19.8

42 25.9 109.9 321./20.0

48 25.9 110.1 281./ 1.8

54 25.9 110.1 162./ .9

60 26.7 110.8 320./10.9

66 26.9 110.9 344./ 2.2

72 27.4 111.2 322./ 5.5

78 27.3 111.3 212./ 1.3

84 27.8 111.8 312./ 6.8

90 28.0 112.0 332./ 2.3

96 28.3 112.3 313./ 4.1

102 28.9 112.8 320./ 7.3

108 28.9 112.8 27./ .4

114 29.0 112.7 60./ .7

120 28.9 112.7 225./ .3



STORM DISSIPATED AT 120 HRS AT THE ABOVE PSN
Member Since: July 15, 2006 Posts: 174 Comments: 54372
Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2
Member Since: October 1, 2007 Posts: 81 Comments: 26511
You guys are great! Thanks. Have a great day.
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1655. Dakster
It is raining really hard in Miami-Dade right now... It is as dark as night out. Weather service says nickel size hail and gusts to 70mph are on its way to us...
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1653. NEwxguy
GM,all,our unwelcomed low up here in the northeast is still hanging around although starting to weaken,but its amazing how far south the circulation goes.
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Quoting Chicklit:
Hi Taz...that's a healthy pattern for us. We love our afternoon thunderstorms here in Florida. It sure helps to cool things off. Thanks!





your welcome
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Hi Taz...that's a healthy pattern for us. We love our afternoon thunderstorms here in Florida. It sure helps to cool things off. Thanks!
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Quoting StormFreakyisher:
Man this is awfully sad.The City of Lake Worth lost power from this storm.FPL always said they are ready for this hurricane season and they "strengthened" power lines.Ha yeah right!


If I remember correctly, Lake Worth built its own power grid many, many years ago, and it's a less efficient and weaker grid system than what is generally in use throughout the area.
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Quoting Chicklit:
StormW, Thanks.
As usual, explanations create more questions.
With a stronger El Nino, shouldn't we see stronger Caribbean westerlies? Do we usually see a strong westerly wind in the Caribbean in June/July? Please explain what's happening over Florida according to the shear map below.


whats going on overe FL right now is this your day time/AM t-storms
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Quoting DeerfieldBeachGuy:
Good morning from Deerfield Beach. Was awakened by a lightning strike that must have only been yards away from my condo. Nasty area of thunderstorms just came thruough here---wind really picked up and the lightning could only be described as excessive.

Stay safe everyone!
I'm in Deerfield as well and those strikes were intense to say the least. Where are you in Deerfield Beach? I'm in The Cove area on the border of Lighthouse Point. Seems to be settling down now and ooks like a good window to get out of the house and head to work.
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oh Please a 70mph TS at landfall sould be fun i take a 70mph overe a 170mph cat 5 at land fall any day
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Good Morning All....Storm, Ike & 456 have us covered again this AM I see. Atlantic quiet out there right now cept for the three areas of interest but sheer continues to rule at the moment....Most interesting area, for me, is the apparent trof remnant near the Bahamas..Seems to have the classic "look" but under 20 knots of sheer. Driving tommorow morning from Apalachicola to Orlando for a conference and then on to Ft. Lauderdale for the weekend (with old buddies) for some beer, music, and much needed break...Hope I don't get too many showers on the way but I don't think I will escape the heat anyway you look at it....Bringing plenty of t-shirts and shorts for the trip. Have a great day/week and see Yall next week....WW
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StormW, Thanks.
As usual, explanations create more questions.
With a stronger El Nino, shouldn't we see stronger Caribbean westerlies? Do we usually see a strong westerly wind in the Caribbean in June/July? Please explain what's happening over Florida according to the shear map below.
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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.