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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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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Quoting hurricane2009:
East Coast Seabreeze has moved inland in Florida

Energy is diving South from GA as well could get quite active in CFL later
Member Since: July 7, 2005 Posts: 0 Comments: 5417
Possibe 93L is going through the usual DMIN effects, will likely blow up Tonight.
Wouldn't surprise me to wake up with an Orange Alert.
Member Since: July 8, 2005 Posts: 259 Comments: 24576
1291. centex
nws cctx - WOULD NOT BE SURPRISED IF THIS
SYSTEM BECOMES A DEPRESSION BEFORE MAKING LANDFALL.

We need it and hope remants move up into south Texas.

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1290. IKE
Quoting CycloneOz:


As I continue to think about it...wasn't it four instruments, mounted in a "square" pattern and the camera went around them like in a circle? Seems that's what I recall...wind, baro, temp, clock (time)?


I remember that pattern, but I also remember it going back and forth and I remember it would stick every once and awhile.
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1288. Levi32
Quoting DestinJeff:


doing that makes you cool though


Lol I swear if I ever got a job writing a NWS discussion I wouldn't assume everyone knew what I was talking about. That kind of short-hand belongs only in iPhones and blackberries..
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1283. Levi32
Quoting btwntx08:
look what the nws in corpus christi had to say about boc system...
000
FXUS64 KCRP 222019
AFDCRP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CORPUS CHRISTI TX
319 PM CDT MON JUN 22 2009

.SHORT TERM (TONIGHT THROUGH TUESDAY NIGHT)...THE MAIN FCST
CONCERN WL BE THE TRACK OF THE TROPICAL DISTURBANCE CURRENTLY
EAST-SOUTHEAST OF TAMPICO MEXICO. VISIBLE SATL IMAGERY CONTINUES
TO INDICATE THIS SYSTEM IS BECOMING BETTER ORGANIZED. ANITCYLONIC
OUTFLOW ALOFT WAS ALSO NOTED ON THE NORTHERN AND WESTERN SIDE OF
THIS SYSTEM. GIVEN ALL OF THIS...WOULD NOT BE SURPRISED IF THIS
SYSTEM BECOMES A DEPRESSION BEFORE MAKING LANDFALL TUE EVENING
BETWEEN TAMPICO AND BROWNSVILLE.
WL LEAN TWDS THE ECMWF AND GFS
SOLNS SINCE THEY HAVE BEEN THE MOST CONSISTENT WITH THE TRACK OF
THIS SYSTEM. AS A RESULT...THE BRUNT OF THE DEEP TROPICAL MOISTURE
ASSCTD WITH THIS SYSTEM WL TRACK ACROSS NRN MEXICO AND DEEP SOUTH
TX ON TUE AND TUE NIGHT. OUR CWA WL REMAIN ON THE NRN FRINGE OF
THIS SYSTEM AS THE MAIN CORE TRACKS WEST-NORTHWESTWARD THROUGH
NRN MEXICO AND DEEP SOUTH TX ON TUE AND TUE NIGHT. PREFER THE GFS
MOS POPS WHICH CARRY LOW CHC POPS ACROSS THE EXTREME SRN PORTION
OF THE CWA WITH SLIGHT CHC POPS ELSEWHERE. THE NRN AREAS WL
REMAIN MOSTLY DRY AS THE RDG AXIS ALOFT WL HAVE MORE OF AN
INFLUENCE ACROSS THIS PARTICULAR AREA. HIGHS ACROSS THE NRN AREA
WL REMAIN WELL ABV NORMAL AS A RESULT OF THIS RDG AXIS ALOFT AND
DRY SOIL CONDITIONS. FURTHER SOUTH...THERE WL BE A SLIGHT REPRIEVE
FROM THE HEAT AS INCREASED CLOUD CVR AND PCPN CHCS WL "COOL" OFF
TEMPS BY SVRL DEGS FROM WHERE THEY HAVE BEEN OVER THE PAST SVRL
DAYS.



"better organized" isn't quite the phrase I'd use to describe it but oh well....he's a meteorologist I'm not.

The system is ragged with the mid-level center displaced to the NW of the surface reflection and spreading out the energy. There isn't much energy to go around in the first place with Andres taking most of it. This system in the Bay of Campeche can't afford to spread out. It needs to consolidate and get vertically stacked if it's going to have a chance before being pushed inland by the high to the north.
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A must have wallpaper
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1279. IKE
Quoting CycloneOz:


Wow...we were watching the same channel. I remember the back and forth between the instruments! Very cool in a low-tech way! Those days are long...long gone! :)


It's a small world.
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1276. There is definatly potential. The convective waning right now is just a diurnal effect.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1277. KEEPEROFTHEGATE (Mod)
hey ike and oz

79 was the year i got my very first computer the old commode 64 with tape deck and the giant modem that you had to put the phone receiver on sat images then were really fuzzy and difficult to disect but i learned and over time the computer got better and better dos was main operating system then i still remember most of those commands but there useless now
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1274. Levi32
Quoting GatorWX:
Also, looks like shear is putting a hamper on Andres development. Put on a nice show of intensification last night though.


The shear is mostly an illusion. Andres is under an elongated upper-level anticyclone that extends to his northwest. Andres' own outflow is registering as shear but the system can't harm itself with its own outflow. The bigger problem for Andres is his proximity to an upper low to his north over central Mexico that is cutting off his poleward outflow channel.

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Its so hot here the sky is crying again. Translation its raining under the heat ridge. Lol. No one knows why. Gotta love the weather. :)
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1272. KEEPEROFTHEGATE (Mod)
Quoting IKE:
I stayed up all night too when Eloise hit. Lived in Panama City...on the east side.

I remember Panama City area offered cable TV(which my folks had), and had a station that showed current weather conditions. It had a clock sized figure for temp, BP, wind speed...wind direction, etc.

TV camera would scroll left to right...then right to left, showing each measurement.

I noticed the wind reading gusting to around 50 mph between 3-4 am. Cable soon when out after that and was off for about a month.
i was ten years old in 75 and storms then were not even on my mind not till 79 did i start to watch and learn
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting KEEPEROFTHEGATE:
its called the day effect went the sun goes down the storm will ramp up
wait watch see


Diurnal effects are less of an issue for developed cyclones. Shear is inhibiting rapid development.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1270. KEEPEROFTHEGATE (Mod)
Quoting GatorWX:
Also, looks like shear is putting a hamper on Andres development. Put on a nice show of intensification last night though.
its called the day effect went the sun goes down the storm will ramp up
wait watch see
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1269. GatorWX
Also, looks like shear is putting a hamper on Andres development. Put on a nice show of intensification last night though.
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1268. IKE
I stayed up all night too when Eloise hit. Lived in Panama City...on the east side.

I remember Panama City area offered cable TV(which my folks had), and had a station that showed current weather conditions. It had a clock sized figure for temp, BP, wind speed...wind direction, etc.

TV camera would scroll left to right...then right to left, showing each measurement.

I noticed the wind reading gusting to around 50 mph between 3-4 am. Cable soon went out after that and was off for about a month.
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1267. Skyepony (Mod)
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.

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1266. beell
There ya go h2009@1257.!

Sea Breeze coming ashore on the E coast of FL.
A little bit of speed shear going up through the layers. All unidirectional from the north pretty much except near/at surface. But not too strong. Best surface convergence right now just W and S of the Cape.

Best upper level support and moisture would seem to be confined to the easter half of the Peninsula.

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Uhhhhgh. I gladly would take winter...
Member Since: August 16, 2007 Posts: 6 Comments: 12463
1264. GatorWX
Quoting centex:
In case you haven't seen this image taken 6/12 from space station. Sarychev Peak on Matua Island NE of Japan. Amazing pic.


That's a really interesting pic! I've never seen a pic from space of an eruption bursting into the atmosphere like that, at least as close up. Pretty cool! Thanks for posting. Looks like BOC low will be inland before anything can ever happen. The 2nd rotation to it's SE isn't helping it any either. Hopefully it'll bring some moisture to those in need in TX and Mexico though.
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1261. KEEPEROFTHEGATE (Mod)


latest surface anal. as of 2100
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1260. KEEPEROFTHEGATE (Mod)


latest ir hurricane floater gom/nwcarb/west atl
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Blog Update
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1258. centex
In case you haven't seen this image taken 6/12 from space station. Sarychev Peak on Matua Island NE of Japan. Amazing pic.
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1256. KEEPEROFTHEGATE (Mod)
Quoting Levi32:
I did not feel the earthquake here.
thats a good thing then levi
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1255. Ossqss
Magnitude Location Time
5.5 Andreanof Islands, Aleutian Islands, Alaska 1 hour ago Map
5.4 Southern Alaska 1 hour ago Map
4.4 Central California 2 days ago


Last 7 days fixed link
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1253. Levi32
I did not feel the earthquake here.
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At the rate of it is moving, it will be inland soon. NHC just has the propensity to say "over the next 48hrs".
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Daniel from weather Weast has this update his blog on El Nino


Quiet summer pattern continues; El Nino now a near-certainty

After a very active start to the normally meteorologically quiescent month of June, we have now entered a more typical summer regime. Temperatures across the state are relatively cool at the moment, but these are expected to trend towards or even a little above seasonal normals by later this week. The models are currently indicating a small possibility that a weak cutoff low near the SoCal coast will draw a bit of moisture northward from Tropical Storm Andres, but this looks somewhat unlikely at the moment. If the situation changes and a larger volume of moisture is advected into the southerly flow aloft, I will update later this week.

More interesting and certainly more important in the long term is the evolving ENSO event in the Pacific. SST warming has been significant in the past few weeks and positive anomalies are now well-established in all Nino regions. In fact, average anomalies are now around 0.7 degrees C basin-wide. Should the present anomalies persist for the next two months, we would officially have a weak El Nino on our hands by August. All indications, however, are that the warming of the tropical East Pacific will continue, and that anomalies wil continue to increase with time. Dynamical climate models are unanimous in predicting El Nino conditions for the coming fall and winter, and even the statistical models have now come into line. This is very early to be experiencing significant El Nino-related warming of the sea surface, which may be an indication of the eventual magnitude of the event. There does appear to be some correlation between early onset of El Nino and moderate to strong events. Additionally, the frequency of strong El Nino events appears to be 10-15 years (though this is determined by a relatively small sample size–4 events between 1960 and 2009). Since the last major El Nino was 12 years ago, we do appear to be statistically “due” for another. The next 2-3 weeks will be interesting, and it will be informative to watch the SST anomaly maps and dynamical model forecasts. Right now, I would say that there is a near-certainty that a weak El Nino event will develop by September and a very strong possibility that it will continue to strengthen to a moderate event by October. What happens beyond the fall is uncertain, but there is a real possibility (probably less than 50%, but this is still a large number) that El Nino will continue to strengthen and become strong by the beginning or middle of next winter. Should this occur, there would likely be significant implications for the state of CA. Even if the event peaks in the moderate category, I would expect some impacts to be felt at least in SoCal. A quick glance at strong SST anomalies right off the CA coast and a recollection of the recent anomalous weather events in CA may indicate that an El Nino-type circulation pattern already exists and has been influencing CA weather. In any case, I will be updating on the ENSO scenario occasionally through the summer and into the fall. Stay tuned…and the Seasonal Outlook will be updated after the new weekly SST maps come out on Wednesday.
Member Since: May 21, 2006 Posts: 5091 Comments: 115454
Quoting KEEPEROFTHEGATE:
and it will get hotter still got the hottest part of the season to come july and first have august


SSTs peak in September, due to the lag between Sun and Ocean

Example:



Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting KEEPEROFTHEGATE:
i wonder if levi felt the earth move


Alaska is Big... lots of room to dampen..
Though by the map he may of felt in Kenai.

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ocean water temps here were 89 degrees on Sunday when I went to the beach.

Today we had a high air temp of 91.9 on my Davis PWS but our island temps are always a little cooler than the mainland.
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Andres: Solid CDO with tight curve banding

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1244. IKE
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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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