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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We are all just Riders on the Blog Make it a good rest of the day!
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Quoting aquak9:
(shakes hands with gator23....paparrazzi walks away, disappointed)


LOL! awesome! High fives aquak9 (aquak9 walks away with a sore hand)
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Quoting K8eCane:
because i can be the first one to jump into a fight and i wish yall wouldnt tempt me


sure why not. We were talking through our disagreement like adults. healthy debate is what blogs are about. we have worked it out civilly. thank you.
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(shakes hands with gator23....paparrazzi walks away, disappointed)
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and its as hot as ell here in Wilmington nc
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Quoting aquak9:
well gator, then there was a definite misunderstanding. By quoting me, I had to assume you were addressing me.

"End of story" is a rather brutal phrase that tends to shut out others. My apologies if this was unwarranted.


No apologies warranted. We are here for the same reason. there are folks on here who flame this blog. I am not one of them. i understand your defense given that many people on this blog are here just to troll
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because i can be the first one to jump into a fight and i wish yall wouldnt tempt me
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I thought I read earlier that there was a slight risk of "severe" weather tomorrow (West Palm), but increasing Tuesday thru at least Thursday.
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Quoting Tazmanian:
if you guys are going to start fighting take it too your own blogs and not in here or in mail


THANK YOU TAZ AND YES I AM SHOUTING!
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if you guys are going to start fighting take it too your own blogs and not in here or in mail
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well gator, then there was a definite misunderstanding. By quoting me, I had to assume you were addressing me.

"End of story" is a rather brutal phrase that tends to shut out others. My apologies if this was unwarranted.
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Wow looks like Boca is going to be the hottest in south Florida tomorrow with a forecast of 96 degrees while west palm,FT Lauderdale and Miami will be 94.Severe thunderstorms are expected to be really bad tomorrow with the heat index near 110!This is why I live in Boca Raton..not lol.
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Quoting aquak9:
Look, gator23. (or should it be gator13?) I've been here since there was only ONE blog. I've been here when there were less than forty of us. ALL OF US.

There is no "end of story". People will continue to be hurt and killed by weather-related events. Even if you grow out of your interest in weather, the story goes on, good chapters and bad. And longtime, dedicated and caring bloggers will continue to post about these events, whether you're here, or not.

Maybe your story will end, but not ours.


I dont even know what your talking about. I wasnt even talking to you. What i meant was we should not call things fish storms because they always have the potential to cause damage. the end of story thing was
1.not directed at you
2.just a saying
3. I have no idea what you are talking about.
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Quoting aquak9:

Maybe your story will end, but not ours.


+1 :)
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Quoting hurricane2009:
Well excuse me seminolesfan, looks like you are just as sensitive

you should take your own advice really


I'm lighter than air, baby; don't let it be your concern.

o and I'm not real sensitive; just observing from the lectern.
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Look, gator23. (or should it be gator13?) I've been here since there was only ONE blog. I've been here when there were less than forty of us. ALL OF US.

There is no "end of story". People will continue to be hurt and killed by weather-related events. Even if you grow out of your interest in weather, the story goes on, good chapters and bad. And longtime, dedicated and caring bloggers will continue to post about these events, whether you're here, or not.

Maybe your story will end, but not ours.
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Quoting ChrisDcane:
y r there always problems on this blog GEEEEZ!!

y r there always problems on this blog GEEEEZ!!


Not from me. i wasnt even referring to aquak9 she just took it that way.
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y r there always problems on this blog GEEEEZ!!
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Quoting aquak9:
well of COURSE if it had a name, it should be called it's proper name. But quite a few stir-ups don't get named, we call them fish storms, when (after proper enlightenment) I have come to realize that they may cause damage.

No need to "end of story" me, gator23. There's never an "end of story" here on WU.


Unless of course (July 10th) the story does in fact end. (July 10th)
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Shear seems to be weakening in the western Caribbean
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571. IKE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
300 PM EDT SUN JUN 21 2009

...EXTREME HEAT RELAXES SLOWLY INTO THE MIDDLE OF THE WEEK...

.SHORT TERM (TONIGHT THROUGH TUESDAY)...
THE STRONG UPPER LEVEL RIDGE THAT HAS PROVIDED THE FORECAST
AREA WITH THE EXTREME HEAT THE PAST SEVERAL DAYS WILL SLOWLY
RETROGRADE BACK TO THE WEST THROUGH TUESDAY. THIS WILL BE A SLOW
PROCESS...AND ALTHOUGH TEMPS WILL BE SLOWLY DROPPING BELOW HEAT
ADVISORY CRITERIA...IT WILL STILL BE HOT WITH ABOVE AVERAGE TEMPS.

WILL SEE OUR HEIGHTS FALL JUST A BIT ON MONDAY AS THE RIDGE CENTER
SLIPS WESTWARD AND PUTS OUR REGION ALONG THE E/NE PERIPHERY OF THE
CIRCULATION. 850MB TEMPERATURES OF 20-22C SHOULD STILL MIX OUT TO
THE UPPER 90S TO NEAR 101 AWAY FROM THE IMMEDIATE COAST. BEST
CHANCES FOR SEEING THE TRIPLE DIGIT HEAT WILL BE ACROSS THE
WESTERN HALF OF THE AREA (CLOSER TO THE RIDGE AXIS). CURRENT HEAT
INDEX GRIDS...ALTHOUGH UNCOMFORTABLE (104-108 DEGREES)...DO NOT
QUITE REACH HEAT ADVISORY CRITERIA. REGARDLESS...IT WILL BE HOT AND
PRECAUTIONS SHOULD BE MADE BY THOSE PLANNING OUTDOOR ACTIVITIES.
BY TUESDAY THE RIDGE WILL HAVE MOVED FAR ENOUGH WEST THAT TRIPLE
DIGIT HEAT WILL END AS HIGH TEMPS PEAK GENERALLY IN THE MID/UPPER
90S.

AS THE RIDGE RETROGRADES...THE OVERALL CONVECTIVE SUPPRESSION WILL
WEAKEN AS MID-LEVEL TEMPS COOL. THE FASTER NORTH/NW FLOW WILL
ALSO BRING THE POTENTIAL FOR SUBTLE FAST MOVING IMPULSES TO PROVIDE
BRIEF SYNOPTIC SUPPORT FOR LIFT ALONG WITH MORE FAVORABLE MOISTURE
PROFILES. STATISTICAL GUIDANCE OFTEN HAS DIFFICULTY WITH
THESE SUBTLE FEATURES AS THEY ARE TOUGH TO FORECAST MORE THAN A DAY
OR SO IN ADVANCE. POP FORECAST LATE MONDAY AFTERNOON THROUGH THE
REMAINDER OF THE SHORT TERM WILL BE A BIT ABOVE THE STATISTICAL
PACKAGES FOR THIS REASON. WILL KEEP CHANCES IN THE SLIGHT/LOW END
CHANCE (20-35%) FOR KNOW UNTIL CONFIDENCE ON THE TIMING AND STRENGTH
OF ANY IMPULSES INCREASES. CONTINUING A SLIGHT CHANCE FOR THUNDER
ACROSS THE FAR EASTERN ZONES LATER ON MONDAY WHERE SUPPRESSION
SHOULD RELAX THE MOST...AND IN CLOSER ALIGNMENT TO WHERE ANY
IMPULSES MAY BE. EXPANDING THE SLIGHT CHANCE POPS WESTWARD FOR
TUESDAY WITH LOW END CHANCE POPS ACROSS OUR GA/BIG BEND ZONES. BY
MONDAY NIGHT INTO TUESDAY...MOST GUIDANCE SOLUTIONS ARE SHOWING A
WELL DEFINED SURFACE TROUGH STRETCHED OVER THE AREA TO PROVIDE ADDED
LOW LEVEL FOCUS. GENERALLY THIS TIME OF YEAR THE POPS DROP OFF
RAPIDLY WITH THE SETTING OF THE SUN. HOWEVER...UNDER NW FLOW...ANY
MCS MOVING SOUTH INTO THE REGION FROM THE NORTH AND FORCED BY THESE
IMPULSES HAVE THE POTENTIAL TO LAST WELL INTO THE OVERNIGHT
PERIODS.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
well of COURSE if it had a name, it should be called it's proper name. But quite a few stir-ups don't get named, we call them fish storms, when (after proper enlightenment) I have come to realize that they may cause damage.

No need to "end of story" me, gator23. There's never an "end of story" here on WU.
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Quoting seminolesfan:
I love the fact that a handle with the current year as a part is in here playing blog police. If you have an old handle why change it? Have you managed to cast a foul gloom over your old screenname? I'm sure an actual new user that joined this year wouldn't try to exert so much control over the blog.

LIGHTEN UP!!!

We're all here for fun and not profit!!!


To quote the Human Torch, FLAME ON! (July 10th)
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I love the fact that a handle with the current year as a part is in here playing blog police. If you have an old handle why change it? Have you managed to cast a foul gloom over your old screenname? I'm sure an actual new user that joined this year wouldn't try to exert so much control over the blog.

LIGHTEN UP!!!

We're all here for fun and not profit!!!
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Quoting hurricane2009:
and maybe I am oversensitive to this, but I look at it this way;

First off, we here on this site are here because we love to watch the process that these storms go through in terms of development and then in terms of where they go. To automatically say something is a "fish storm" right at its 1st advisory, kinda takes that away from us.

But more importantly I look at the impact of a storm through the eyes of those who could be and are affected by it. I would never say something on here that I wouldnt say to the face of the family of someone who was affected by a storm.


Well said.
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Quoting aquak9:
Maybe we should call them "ship storms" instead?

I will continue to call them by their names since they are life/property threatening tropical systems. End of story.
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562. HadesGodWyvern (Mod)
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Quoting hurricane2009:


A "fish storm" is a slang term meaning a storm that only has effect on fish.

To me this storm will be close enough to the coast, people will be affected. This storm will go out to sea likely as it turns west, that to me is more accurate in terms of describing the eventual direction this storm will take. Out to sea, not fish storm


Storms that form early in that area of the Pacific each year almost always take a turn to the west before they hit the coast but if they slow down and hang around offshore for a few days they can cause a huge amount of damage in little towns like La Manzanilla.

This just feels like the start of a strange Pacific hurricane season to me. Had never heard the term fish storm before - thanks for the education.
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Maybe we should call them "ship storms" instead?
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Quoting hurricane2009:


To me there is a huge difference between predicting when the 1st storm will form and calling a storm a fish storm just after its 1st advisory. No crow for you, if you are wrong, so what, there are very few that are ever right

Touche' sir
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558. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #30
TROPICAL STORM LINFA (T0903)
6:00 AM JST June 22 2009
====================================

Subject: Category One Typhoon Overland South China

At 21:00 PM UTC, Tropical Storm Linfa (992 hPa) located at 25.3N 118.6E has 10 minute sustained winds of 45 knots with gusts of 65 knots. The storm is reported as moving north at 8 knots.

Dvorak Intensity:

Gale Force Winds
==================
100 NM from the center in southeastern quadrant
70 NM from the center in northwestern quadrant

Forecast and Intensity
=======================
24 HRS: 28.6N 121.0E - Tropical Depression
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Quoting IKE:




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Wow, this week will be very hot in S. Ontario, with daily Humidex highs averaging 33C (91F) for the week.
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554. IKE
Quoting SavannahStorm:


Did somebody say fish?



Member Since: June 9, 2005 Posts: 23 Comments: 37858


Did somebody say fish?

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Quoting lamanzanilla:


Can someone explain what a fish storm is to me?



a fish storm is where a storm pop up and gos safey out too sea with out hiting any one other then ships
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Quoting hurricane2009:


To me there is a huge difference between predicting when the 1st storm will form and calling a storm a fish storm just after its 1st advisory. No crow for you, if you are wrong, so what, there are very few that are ever right


Can someone explain what a fish storm is to me?
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Quoting hurricane2009:


To me there is a huge difference between predicting when the 1st storm will form and calling a storm a fish storm just after its 1st advisory. No crow for you, if you are wrong, so what, there are very few that are ever right


Good point you don't get a prize if you are right or anything maybe a bigger ego I suppose.
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Amazing 93 a cool down my local met says if I was still living in New England it would be a massive heat wave.
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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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