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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ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL STORM ANDRES 02E



INITIAL TIME 6Z JUN 22



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 15.0 102.2 290./ 4.1

6 15.4 101.8 44./ 6.1

12 16.2 101.7 6./ 7.6

18 17.2 102.0 346./10.3

24 17.9 102.8 309./10.7

30 18.4 103.9 295./11.9

36 19.3 105.3 302./15.6

42 21.3 106.0 341./20.8

48 21.9 106.0 356./ 6.0

54 22.1 106.4 304./ 4.1

60 22.3 106.8 297./ 4.1

66 22.9 107.3 319./ 7.5

72 23.1 107.5 324./ 2.6

78 23.1 107.6 256./ 1.5

84 23.0 107.6 189./ .6

90 23.0 107.6 0./ .0



STORM DISSIPATED AT 90 HRS AT THE ABOVE PSN.


Member Since: July 15, 2006 Posts: 178 Comments: 56141
W/V image of tropical wave

Link
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Good Morning All.......Shear is still hostile over most of the Caribbean and Gulf, including 20 knots of sheer over that Blob in the BOC, but, looks like a rainmaker for that region of Mexico...Sheer continues to rule the tropical Atlantic at this time.
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tropical wave being ripped apart by 40 knots westerly shesr


href="ww.ssd.noaa.gov/goes/east/catl/loop-wv.html" target="_blank">Link
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Andres QS
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Morning everyone. Anyone use Virtual Weather Station? I need a little help with one of the features... It's for this:


Photobucket
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thanks weather 456. i was only being sarcastic. i posted an erlier link concerning the upper level enviroment
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Yet it persists.
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Quoting stoormfury:
wonder what is the take on atl tropical wave from Hurricane 2009 and Aussie Storm?


I inlcuded it in my update if you would like to see but upper winds are just too unfavorable.
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Barbados should be waking up with this blob creature in their neighborhood.
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wonder what is the take on atl tropical wave from Hurricane 2009 and Aussie Storm?
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Wave at 54W 10N is certainly getting my attention. Lets see if the shear will tear it apart this morning.
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Good Morning;

Tropical Storm Andreas & The Atlantic

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very hostile upper level environment in the tropical atlantic this morning

Link
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Pretty good flare up with the wave at 52w and a nice blob off of the Fla coast
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728. HadesGodWyvern (Mod)
Japan Meteorological Agency

Tropical Disturbance Summary (0600z 22JUN)
===========================================
At 15:00 PM JST, Low Pressure Area (1006 hPa) located at 11.0N 132.0E is reported as moving west-northwest slowly.

Philippines Atmospherical Geophysical Astronomical Services and Administration

Tropical Weather Outlook
===========================
At 2:00 PM PhST, An Active Low Pressure Area was estimated based on satellite and surface data 540 kms east of Visayas (10.5N 131.2E) embedded along the Intertropical Convergence Zone affecting Visayas and Mindanao.

Joint Typhoon Warning Center

Tropical Disturbance Summary (0600z 22JUN)
============================================
An area of convection (92W) located at 9.7N 133.0E or 175 NM north-northwest of Palau. Animated multispectral satellite imagery depicts cyclonic flow around a developing low level circulation center north of Palau moving generally westward. A 2131z SSMI image image indicates the presence of a broad low level circulation center with convective banding beginning to wrap into the low level circulation center. Also, a 1642z AQUA microwave image indicates convective banding around a broad mid to low level circulation. Upper level analysis indicates the feature is encountering low vertical wind shear.

Maximum sustained winds near the center is 12-18 knots with a minimum sea level pressure of 1009 MB. Since the low level circulation is becoming more organized, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is UPGRADED TO FAIR.
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727. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #33
TROPICAL DEPRESSION, FORMER LINFA (T0903)
15:00 PM JST June 22 2009
====================================

At 6:00 AM UTC, Tropical Depression, Former Linfa (998 hPa) located at 27.0N 120.0E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving northeast at 15 knots.

This is the final tropical cyclone advisory
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Nice CDO on Andres.
Member Since: July 8, 2005 Posts: 259 Comments: 24580
From my local NWS LAKE CHARLES, LA

LOL...

ISOLATED STREAMER SHOWERS ENDING WITH LOSS OF DAYTIME HEATING.
WILL KEEP 10 PERCENT POP MAINLY ALONG AND SOUTH OF THE I-10 CORRIDOR
BETWEEN LAFAYETTE AND BEAUMONT. HOWEVER...THIS WILL ONLY BE SEEN IN
THE GRIDDED GRAPHICS SINCE THE POPS ARE TO LOW TO MENTION IN THE
ZONE FORECAST FOR TONIGHT. YOUR CHANCE OF SEEING A SHOOTING STAR
IS HIGHER THAN THE PROBABILITY OF RAIN TONIGHT.
TEMPERATURES LOOK
GOOD...SEE NO REASON TO ADJUST FORECAST. MAY SEE SOME LIGHT PATCHY
FOG LATER TONIGHT...BUT SHOULD BE BRIEF. NO CHANGES TO ZONE FORECAST
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00
WTPZ32 KNHC 220833
TCPEP2
BULLETIN
TROPICAL STORM ANDRES ADVISORY NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022009
200 AM PDT MON JUN 22 2009

...ANDRES STRENGTHENS A LITTLE MORE WHILE MOVING SLOWLY...

A TROPICAL STORM WATCH REMAINS IN EFFECT FROM ZIHUATANEJO MEXICO
NORTHWARD TO MANZANILLO MEXICO. A TROPICAL STORM WATCH MEANS THAT
TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH
AREA...GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE ALONG THE SOUTHWESTERN COAST OF MEXICO SHOULD
MONITOR THE PROGRESS OF ANDRES.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 200 AM PDT...0900 UTC...THE CENTER OF TROPICAL STORM ANDRES WAS
LOCATED NEAR LATITUDE 15.0 NORTH...LONGITUDE 102.1 WEST OR ABOUT 190
MILES...305 KM...SOUTH OF ZIHUATANEJO MEXICO AND ABOUT 310 MILES...
505 KM...SOUTH-SOUTHEAST OF MANZANILLO MEXICO.

ANDRES IS MOVING TOWARD THE WEST-NORTHWEST NEAR 3 MPH...6 KM/HR...
AND A SLOW WEST-NORTHWEST TO NORTHWEST MOTION IS EXPECTED TO
CONTINUE DURING THE NEXT 24 TO 48 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST...AND ANDRES COULD BECOME A
HURRICANE DURING THE NEXT COUPLE OF DAYS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 997 MB...29.44 INCHES.

LOCALLY HEAVY RAINS ARE POSSIBLE OVER PORTIONS OF SOUTHERN AND
SOUTHWESTERN MEXICO DURING THE NEXT DAY OR TWO.

...SUMMARY OF 200 AM PDT INFORMATION...
LOCATION...15.0N 102.1W
MAXIMUM SUSTAINED WINDS...50 MPH
PRESENT MOVEMENT...WEST-NORTHWEST OR 300 DEGREES AT 3 MPH
MINIMUM CENTRAL PRESSURE...997 MB

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 500 AM PDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 800
AM PDT.

$$
FORECASTER PASCH
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Sorry but the home grown stuff always gets me this time of year. The nonsense that just left our coast and is floating around just irritates me.
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722. 7544
ouch nice blow up just east of fla dipping south at this hour Link
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Quoting weatherblog:
I don't see any development in the BOC (or anywhere else in the basin) in the near-term. Just from looking at shear maps alone, shear is very high. Until that lets up, I don't expect any development in the caribbean, GOM, etc in the next 5 days unless a system were to find a small pocket of shear or conditions improve rapidly.

On the other hand, I think Andres will probably be a strong tropical storm/hurricane in under 24 hours or so. It could even be a threat to the Baja Peninsula, but right now I'd say not a big one.


I agree....BOC clears up in 24-48 hours...Caribbean in 96-144. The eastern Gulf of Mexico needs to be watched as well as the trough split occurs and pressure lower near Florida along the tail-end of the frontal boundary associated with the extratropical low-pressure system off the US east coast.
Member Since: November 24, 2005 Posts: 635 Comments: 26701
I don't see any development in the BOC (or anywhere else in the basin) in the near-term. Just from looking at shear maps alone, shear is very high. Until that lets up, I don't expect any development in the caribbean, GOM, etc in the next 5 days unless a system were to find a small pocket of shear or conditions improve rapidly.

On the other hand, I think Andres will probably be a strong tropical storm/hurricane in under 24 hours or so. It could even be a threat to the Baja Peninsula, but right now I'd say not a big one.
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Quoting hurricane2009:


well said Levi, we will see what happens in the BOC, probably still a few days away

Andres is the big game in town right now

Night


Yup, night H2009
Member Since: November 24, 2005 Posts: 635 Comments: 26701
Well the BOC isn't that far of a fetch because Andres' competing circulation to its east is moving north towards the BOC, and an upper ridge is forecast to build over that area during the next 24-48 hours. If anything this is the start of the northward push of moisture I've been talking about since the beginning of June.

I really don't see the extratropical low spawning anything beyond cold-core. It's not a terribly spread-out system so the baroclinic zone should prevent any trouble from trying to get going, but of course that's just my opinion.
Member Since: November 24, 2005 Posts: 635 Comments: 26701
Quoting Levi32:


30n 70w part of the extratropical system. It doesn't really seem like a threat to me.



I personally am looking towards the BOC for possible development seeing as that has a tendencey to be a more favorable area for tropical cyclone development although the extra-tropical low is given the right conditions and time, there is a small possibility that it could develop into something non/sub-Tropical.
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Quoting hurricane2009:
Teddy where is that second pic from?


30n 70w part of the extratropical system. It doesn't really seem like a threat to me.

Member Since: November 24, 2005 Posts: 635 Comments: 26701
Quoting hurricane2009:
Teddy where is that second pic from?

Off South Carolina.
Member Since: July 8, 2005 Posts: 259 Comments: 24580
Daily Tropical Area of Interest 1;

Summary: Moister from the Pacific is in the BOC, this is a climatology favored area for tropical Cyclone Development, So we will have to watch it.
Daily Tropical Area of Interest 2;

Summary: This area is also in a climotology favored area, and If I remember not to long ago models were hinting at development in this area.

Member Since: July 8, 2005 Posts: 259 Comments: 24580
big bend national park in West Texas
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theres a big ben in london...... :)
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the big bend area is the area along FL gulf coast where the panhandle meets the peninsula,its a big bend along the coastline,hence the phrase "the big bend":)
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Quoting Levi32:


Well gee even I know that! And I'm an Alaskan lol. =P


I know a couple big bends, and two of them are not even in the states :)

BTW, isn't there a big bend in Indiana or something?


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Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2

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Quoting Orcasystems:
WTH is big bend area?


Well gee even I know that! And I'm an Alaskan lol. =P
Member Since: November 24, 2005 Posts: 635 Comments: 26701
Quoting hahaguy:


The crescent shape in the Florida Panhandle.


Ahh ok :)
Thank you
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Quoting Orcasystems:
WTH is big bend area?


The crescent shape in the Florida Panhandle.
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TD2 w/be a hurricane before tuesday night,IMO
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WTH is big bend area?
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I'm thinking we might actually get a invest in the BOC over the next 48hrs as the a area of disturbed wx moves north from the east pac over mexico into the area...and/or possibly a another disturbance forming offshore of the big bend area in about 48-72hrs!!!!!....things could change quickly in the tropics close to home,I'm not saying that it'll happen,but w/mother nature one never knows!!!!;)
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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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