Dust forecast for the 2009 Atlantic hurricane season

By: Dr. Jeff Masters , 6:58 PM GMT on June 20, 2009

Share this Blog
5
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1594 - 1544

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

1594. HadesGodWyvern (Mod)
India Meteorological Department
Tropical Cyclone Warning Number TWO
DEPRESSION ARB01-2009
8:30 AM IST June 23 2009
==================================

Subject: Depression over east central Arabian Sea

At 3:00 AM UTC, Depression ARB01-2009 located at 19.0N 71.5E, or about 150 km west of Mumbai and 300 km south-southwest of Surat.

3 minute sustained winds near the center is 25 knots with a central pressure of 998 hPa. The state of the sea is rough to very rough around the system's center.

Satellite imagery indicates gradual organization of convection during the past 12 hours. The intensity of the system is T1.5. Associated broken low /medium clouds with embedded intense to very intense convection seen over Arabian Sea between 16.5N and 21.0N and to the east of 67.0E. The lowest cloud top temperature due to convection is around -70C

Vertical wind shear of horizontal wind over the region is low to moderate (around 10-20 knots). Sea surface temperature is favorable for intensification and is 0.50 to 1.00C above normal. The system lies embedded in the southwesterly flow in lower and middle levels. The upper tropospheric ridge roughly runs along 21.0N.

Considering all the above, the system is likely to intensify into a deep depression and move in a north-northeasterly direction and cross south Gujarat coast near Surat by this evening/night.
Member Since: Posts: Comments:
Station SBPT2 - 8770570 - Sabine Pass North, TX
Air Temperature (ATMP): 81.9 °F
Water Temperature (WTMP): 88.2 °F

Station GPST2 - 8771510 - Galveston Pleasure Pier, TX
Air Temperature (ATMP): 82.8 °F
Water Temperature (WTMP): 91.8 °F

Station GTOT2 - 8771450 - Galveston Pier 21, TX
Air Temperature (ATMP): 82.8 °F
Water Temperature (WTMP): 94.8 °F

Yep! They are toasty here out west. And that highs not moving off us for a while. :)
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
----- Current Analysis -----
Date : 23 JUN 2009 Time : 034500 UTC
Lat : 16:52:39 N Lon : 103:10:29 W


CI# /Pressure/ Vmax
4.2 / 986.0mb/ 69.8kt


Final T# Adj T# Raw T#
(3hr avg)
4.1 4.3 4.3

Latitude bias adjustment to MSLP : +2.2mb

Center Temp : -73.9C Cloud Region Temp : -74.9C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : EAST PACIFIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : OFF

****************************************************
looks like a cat 1 at 69 kts but weakening flag is on may not be one for to long


aye, but the Constraints are off.
Member Since: Posts: Comments:
That high anchored over the Gulf has had a pretty dramatic effect on SST's...
Member Since: Posts: Comments:
Quoting washingaway:


Working for me.


Quoting Levi32:


No...00z GFS


Thanx guys - java hung / rebooted!
Member Since: Posts: Comments:
Quoting Kowaliga:
I can't get the 0Z - is ncep down?


Working for me.
Member Since: Posts: Comments:
1588. Levi32
Quoting Kowaliga:
I can't get the 0Z - is ncep down?


No...00z GFS
Member Since: Posts: Comments:
I can't get the 0Z - is ncep down?
Member Since: Posts: Comments:
1585. HadesGodWyvern (Mod)
Philippines Atmospherical Geophysical Astronomical Services and Administration

Tropical CYclone Bulletin #2
===========================
At 11:00 AM PhST, Tropical Storm Feria located at 11.3°N 126.4°E or 100 kms east of Borongan, Samar has 10 minutes sustained winds of 65 km/h (35 knots) with gusts of 80 km/h (45 knots).

Signal Warnings
===============

Signal Warning #2 (60-100 kph winds)

Luzon Region
-----------
1.Masbate
2.Ticao Island
3.Sorsogon
4.Albay

Visayas Region
-------------
1.Samar Provinces
2.Leyte
3.Biliran Island

Mindanao Region
----------------
1.None

Signal Warning #1 (30-60 kph winds)

Luzon Region
-----------
1.Camarines Provinces
2.Southern Quezon
3.Catanduanes
4.Burias Island
5.Romblon
6.Marinduque

Visayas Region
-------------
1.Southern Leyte
2.Camotes Is.
3.Cebu
4.Bohol
5.Northern Negros
6.Capiz
7.Iloilo
8.Aklan

Mindanao Region
----------------
1.Dinagat Is.
2.Siargao
3.Surigao del Norte
4.Camiguin

Additional Information
========================
Residents living in low lying areas and mountanous including coastal areas under signal #2 and 1 are alerted against possible flashloods and landslides.

The public and the disaster coordinating councils concerned are advised to take appropriate actions and watch for the next bulletin to be issued at 5 P.M. today.
Member Since: Posts: Comments:
1584. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1583. KEEPEROFTHEGATE (Mod)
lol
miss it mishy
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1582. KEEPEROFTHEGATE (Mod)
was somebody fighting did'nt see it
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1581. KEEPEROFTHEGATE (Mod)
Quoting AussieStorm:

Whats the temps deeper down?
not sure aussie but i know it has to be at 160 ft at least
Member Since: July 15, 2006 Posts: 178 Comments: 56141
MX from the E PAC looks like its going to be geting hit in fac it looks like it will be makeing land fall here soon or some time on tuesday
Member Since: May 21, 2006 Posts: 5091 Comments: 115456
Who's fighting? We all LOVE each-other.Its just spirited dicussions!
Member Since: Posts: Comments:
Quoting vortfix:
Nobody is fighting Mishy.

k
Member Since: Posts: Comments:
Quoting Orcasystems:


Hi Mishy.. whos fighting?
What did I miss?
ORCA the whale!!! How are you? I was reading some post from people on here.
Member Since: Posts: Comments:
1575. Levi32
Andres' inner core structure still appears to be rather ragged. The system is trying to form an eyewall but isn't quite strong enough yet. That's why we usually only see eyes in hurricanes and not in tropical storms since they are weaker.

Member Since: Posts: Comments:
Quoting TampaMishy:
Why does everyone fight on here?


Hi Mishy.. whos fighting?
What did I miss?
Member Since: Posts: Comments:
Quoting AussieStorm:

Whats the temps deeper down?

I deleted it.. it was 3 days old..
Member Since: Posts: Comments:
1572. Levi32
Quoting AussieStorm:

Whats the temps deeper down?


This should give you an idea.

Depth of the 26C isotherm (how deep the layer of water is that is warm enough to support TC development):

Member Since: Posts: Comments:
Why does everyone fight on here?
Member Since: Posts: Comments:
I see some mean looking thunderstorms off the east coast of florida, is this the welcoming party of the so called possible severe weather that will be around for the next day or 2?
Member Since: Posts: Comments:
Quoting Orcasystems:


Looks like a hot soup.

Whats the temps deeper down?
Member Since: Posts: Comments:
1568. KEEPEROFTHEGATE (Mod)
----- Current Analysis -----
Date : 23 JUN 2009 Time : 034500 UTC
Lat : 16:52:39 N Lon : 103:10:29 W


CI# /Pressure/ Vmax
4.2 / 986.0mb/ 69.8kt


Final T# Adj T# Raw T#
(3hr avg)
4.1 4.3 4.3

Latitude bias adjustment to MSLP : +2.2mb

Center Temp : -73.9C Cloud Region Temp : -74.9C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : EAST PACIFIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : ON
Rapid Dissipation Flag : OFF

****************************************************
looks like a cat 1 at 69 kts but weakening flag is on may not be one for to long
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting hurricane2009:
Severe Thunderstorm Watch has been dropped for all but two counties

It is still in effect for...

Brevard and Indian River counties until 1am


better watch out later today then!
Member Since: Posts: Comments:
.
Member Since: Posts: Comments:
1565. Levi32
Quoting GetReal:
Levi save it to your blog favorite links....


I will....need to update that list it's 3 years old. That's why I created this
Member Since: Posts: Comments:
1564. GetReal
Levi save it to your blog favorite links....
Member Since: Posts: Comments:
Look on the bright side people, there may be, somewhere, lurking, a remnant of Karen, ready to regenerate at any time. I will check back tomorrow, to see about Andres, even if it is in the EPAC, and on the low chance of that BOC cluster developing. This blog is more entertaining and addictive than a soap opera. Only June, and already drama.
Member Since: Posts: Comments:
1561. Levi32
Quoting GetReal:


Reynolds SST Analysis


Oh wow right under my nose....thanks GR.
Member Since: Posts: Comments:
1560. GetReal
Quoting Levi32:


Care to share?


Reynolds SST Analysis
Member Since: Posts: Comments:
1559. Levi32
Quoting GetReal:
Ajcam I sent you the link I think you were looking for... with the SST archives...


Care to share?
Member Since: Posts: Comments:
1558. GetReal
Ajcam I sent you the link I think you were looking for... with the SST archives...
Member Since: Posts: Comments:
Thanks, I will...off to sleep now, but if anyone can find the link...please mail it to me...

1552. Levi32 11:24 PM CDT on June 22, 2009
Quoting ajcamsmom2:
If anyone has a link to the data I'm looking for, could you please send it to me??? I am not looking for maps, just easy to understand numbers...Thanks


1494. ajcamsmom2 10:05 PM CDT on June 22, 2009
last year someone gave us a link to a monthly sst data chart where you could see the average temps for any given month that went back several years...does anyone have the link???




BTW I'm sorry your request keeps getting ignored lol. I don't have the link, and I looked for it in vain. I'm sure it will turn up if you keep posting that during the main blogging hours.
Action: Quote | Ignore User
Member Since: Posts: Comments:
1554. KEEPEROFTHEGATE (Mod)
Quoting catfuraplenty:
If I understood anything anyone was talking about in here, I'd be even more ignorant than I feel already.

Thus far, in layman's terms there is/isn't enough dust in Africa which means we are/aren't going to have more/less dust in the atmosphere months before hand to affect/have no affect on the amount or intensity of tropical systems we see this year because sea surface temperatures are/are not being suppressed/repressed/without estrogen, which will then be aided/unaided/laughed at by an assisting full/partial/neutral/non El Nino/La Nina/La Vida Loca event.

Grand. Now it all makes sense.
yep we have no idea whats too happen after its all said and done
great job isn't it and you can actually get paid for it
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Blog Update
Reflector site for those at work, which now also includes Weather456, daily updates


AOI #1

AOI #2

Member Since: Posts: Comments:
1552. Levi32
Quoting ajcamsmom2:
If anyone has a link to the data I'm looking for, could you please send it to me??? I am not looking for maps, just easy to understand numbers...Thanks


1494. ajcamsmom2 10:05 PM CDT on June 22, 2009
last year someone gave us a link to a monthly sst data chart where you could see the average temps for any given month that went back several years...does anyone have the link???



BTW I'm sorry your request keeps getting ignored lol. I don't have the link, and I looked for it in vain. I'm sure it will turn up if you keep posting that during the main blogging hours.
Member Since: Posts: Comments:
1550. KEEPEROFTHEGATE (Mod)
hello stormw good to see ya even i just learn something from that explanation thank you very much
something new to watch as the season moves along
Member Since: July 15, 2006 Posts: 178 Comments: 56141
1549. Levi32
Quoting hurricane2009:


Well I think we will see more in the ways of storms tomorrow


You're probably right with the high over the northern Gulf retreating westward and a "back-door front" of sorts pushes westward into Florida from the SW Atlantic.
Member Since: Posts: Comments:
If I understood anything anyone was talking about in here, I'd be even more ignorant than I feel already.

Thus far, in layman's terms there is/isn't enough dust in Africa which means we are/aren't going to have more/less dust in the atmosphere months before hand to affect/have no affect on the amount or intensity of tropical systems we see this year because sea surface temperatures are/are not being suppressed/repressed/without estrogen, which will then be aided/unaided/laughed at by an assisting full/partial/neutral/non El Nino/La Nina/La Vida Loca event.

Grand. Now it all makes sense.
Member Since: Posts: Comments:
If anyone has a link to the data I'm looking for, could you please send it to me??? I am not looking for maps, just easy to understand numbers...Thanks


1494. ajcamsmom2 10:05 PM CDT on June 22, 2009
last year someone gave us a link to a monthly sst data chart where you could see the average temps for any given month that went back several years...does anyone have the link???

Member Since: Posts: Comments:

Viewing: 1594 - 1544

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Top of Page

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.

Local Weather

Overcast
38 °F
Overcast

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron