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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Gulf temps are wrong....they are higher than that folks, local news stations showing 90 and 91 respectfully for Galveston's beach waters

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489. HadesGodWyvern (Mod)
India Meteorological Department

Tropical Weather Bulletin (1800z 21JUN)
=======================================
A low pressure area has formed over east central Arabian Sea



Area west of India and south of Pakistan region
Member Since: May 24, 2006 Posts: 52 Comments: 46576
DothanWx.com, Dothan, Alabama (PWS)
Updated: 3 sec ago
Scattered Clouds
100.6 °F
Scattered Clouds
Humidity: 36%
Dew Point: 69 °F
Wind: 5.4 mph from the WNW
Wind Gust: 7.6 mph
Pressure: 29.93 in (Falling)
Heat Index: 107 °F
Visibility: 10.0 miles
UV: 10 out of 16
Clouds:
Scattered Clouds 4800 ft
(Above Ground Level)
Elevation: 300 ft
Member Since: July 8, 2005 Posts: 259 Comments: 24552


humidex 90
Member Since: July 15, 2006 Posts: 176 Comments: 55665
Any of the models predicting something to spin up anytime soon?
Member Since: July 8, 2005 Posts: 259 Comments: 24552
485. HadesGodWyvern (Mod)
India Meteorological Department

Tropical Cyclone Outlook (0600z 21JUN)
=====================================
Convective clouds are seen over parts of central and northeat Bay of Bengal, north Andaman Sea, and east central and southeast Arabian Sea.

MONSOON WATCH
===============

  • Southwest monsoon has further advanced today, the 21st June 2009, into some more parts of central Arabian Sea, Maharashtra, Karnataka and Andhra Pradesh.


  • The northern limit of monsoon on 21st June 2009 passes through 18.0°N 70.0°E, Alibagh, Pune, Sholapur, Hyderabad, Kalingapatnam, Paradip, Bankura and Gangtok.


  • Conditions are favourable for further advance of monsoon over some more parts of Maharashtra including Mumbai, remaining parts of Karnataka and some more parts of Andhra Pradesh during next 2-3 days.

    Joint Typhoon Warning Center

    Tropical Disturbance Summary (1800z 21JUN)
    ==========================================
    An area of convection (93A) located at 17.1N 68.8E or 260 NM west-southwest of Mumbai, India. Animated multispectral satellite imagery shows and area of convection flaring over a developing low to mid level circulation. A 1414z SSMI-S image shows developing convective banding on the western side of the low level circulation center. Upper level analysis shows that the developing circulation center is in an area of moderate shear, inhibiting deep convection in the area.

    Maximum sustained winds near the center is 15-20 knots with a minimum sea level pressure of 1010 MB. The potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is POOR.
  • Member Since: May 24, 2006 Posts: 52 Comments: 46576
    484. HadesGodWyvern (Mod)
    National Hurricane Center: Miami, Fl

    Tropical Cyclone Outlooks (1800z 21JUN)
    ==========================================
    Showers and thunderstorms associated with the area of low pressure (93E) centered about 175 miles southwest of Acapulco Mexico continues to become better organized.. and a tropical depression appears to be forming. Advisories on this system will likely be initiated later today.

    Heavy rains could affect portion of the southern coast of Mexico during the next day or two.. interest in this region should monitor the progress of this system.

    Tropical Cyclone Formation Potential
    =====================================
    There is a HIGH chance of this disturbance to form into a tropical cyclone within the next 48 hours.

    Joint Typhoon Warning Center

    Tropical Cyclone Formation Alert (1630z 21JUN)
    =========================================
    An area of convection (93E) located at 14.7N 100.3W or 130 NM south of Acapulco, Mexico. Recent animated satellite imagery indicates that although the low level circulation center is broad, it has begun to consolidate. Recent dvorak fixes from KNES and NHC indicates an intensity estimate of 25 knots. Upper level analysis indicates that the system is in a region of upper level diffluence with broad equatorward outflow and a developing poleward outflow channel.

    Maximum sustained winds near the center is 20-25 knots with a minimum sea level pressure of 1003 MB

    System #2
    -----------

    National Hurricane Center

    Tropical Cyclone Outlooks (1800z 21JUN)
    ==========================================
    An area of low pressure located about 1500 miles southwest of the southern tip of Baja California peninsula continues to produce disorganized showers and thunderstorms.. Development of this system, if any will be slow to occur as it moves slowly east-northeast over the next couple of days.

    Tropical Cyclone Formation Potential
    =====================================
    There is a low chance of this disturbance to form into a tropical cyclone within the next 48 hours.
    Member Since: May 24, 2006 Posts: 52 Comments: 46576
    Excessive Heat Warning for Santa Rosa County FL 2:05 pm --- Temp 98 --- Heat Index 106 --- Dew Point 70. My central air is having a tough time keeping up and Gulf Power is loving it.
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    482. HadesGodWyvern (Mod)
    Japan Meteorological Agency
    Tropical Cyclone Advisory #29
    TROPICAL STORM LINFA (T0903)
    3:00 AM JST June 22 2009
    ====================================

    Subject: Category One Typhoon Overland South China

    At 18:00 PM UTC, Tropical Storm Linfa (992 hPa) located at 24.8N 118.5E has 10 minute sustained winds of 45 knots with gusts of 65 knots. The storm is reported as moving north at 7 knots.

    Dvorak Intensity: T3.0

    Gale Force Winds
    ==================
    120 NM from the center in southeastern quadrant
    90 NM from the center in northwestern quadrant

    Forecast and Intensity
    =======================
    24 HRS: 27.9N 120.5E - Tropical Depression



    Overland the Fujian Province of southeastern China.
    Member Since: May 24, 2006 Posts: 52 Comments: 46576
    Member Since: October 1, 2007 Posts: 81 Comments: 26512


    humidex 89
    Member Since: July 15, 2006 Posts: 176 Comments: 55665
    Yea, Tropical Depression 02E

    Member Since: Posts: Comments:
    Member Since: October 1, 2007 Posts: 81 Comments: 26512
    Quoting extreme236:


    Most likely still a TD...other agency kept it as a TD on the reading (T2.0)...nonetheless advisories dont start for anothher 2 hours so you never know



    well see
    Member Since: Posts: Comments:
    Quoting stormpetrol:
    Keep an eye on 11.5N/78W, if it moves more N off of Colombia it could be the next AOI in the SW Carib.IMO.


    Pretty sure its just ITCZ activity...should be nothing worry about.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    Keep an eye on 11.5N/78W, if it moves more N off of Colombia it could be the next AOI in the SW Carib.IMO.
    Member Since: Posts: Comments:
    Can't even move outside its so hot.

    Humidity: 54%
    Dew Point: 77 °F
    Wind: 2.0 mphfrom the WSW
    Wind Gust: 5.0 mph
    Pressure: 29.84 in(Falling)
    Heat Index: 110 °F
    Visibility: 10.0 miles
    UV: 5.6 out of 16
    Member Since: Posts: Comments:
    Quoting Tazmanian:



    cool now we got the 1st name storm cant wait too see what the nhc dos with TD 2E


    Most likely still a TD...other agency kept it as a TD on the reading (T2.0)...nonetheless advisories dont start for anothher 2 hours so you never know
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    Quoting Weather456:
    Most likely 02E at 5PM


    Oh it will be
    invest_RENUMBER_ep932009_ep022009.ren
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    Quoting WPBHurricane05:
    21/1745 UTC 14.6N 101.4W T2.5/2.5 93E--East Pacific



    cool now we got the 1st name storm cant wait too see what the nhc dos with TD 2E
    Member Since: Posts: Comments:
    Most likely 02E at 5PM
    Member Since: Posts: Comments:
    Quoting WPBHurricane05:
    21/1745 UTC 14.6N 101.4W T2.5/2.5 93E--East Pacific


    The other dvorak agency issued a T2.0, which I would assume would be the basis of this not being a TS already.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    445

    WHXX01 KMIA 211826

    CHGE77

    TROPICAL CYCLONE GUIDANCE MESSAGE

    NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

    1826 UTC SUN JUN 21 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



    DISTURBANCE TWO (EP022009) 20090621 1800 UTC



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

    090621 1800 090622 0600 090622 1800 090623 0600



    LAT LON LAT LON LAT LON LAT LON

    BAMS 14.6N 101.3W 15.1N 101.5W 15.9N 101.7W 16.7N 102.2W

    BAMD 14.6N 101.3W 14.8N 101.9W 15.4N 102.5W 16.3N 103.5W

    BAMM 14.6N 101.3W 14.9N 101.7W 15.7N 102.0W 16.7N 102.6W

    LBAR 14.6N 101.3W 15.1N 102.4W 15.8N 103.9W 16.9N 105.7W

    SHIP 30KTS 38KTS 49KTS 57KTS

    DSHP 30KTS 38KTS 49KTS 57KTS



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

    090623 1800 090624 1800 090625 1800 090626 1800



    LAT LON LAT LON LAT LON LAT LON

    BAMS 17.7N 103.2W 19.1N 105.6W 19.6N 108.2W 20.3N 111.8W

    BAMD 17.4N 105.0W 19.0N 109.0W 19.9N 113.6W 20.2N 118.3W

    BAMM 17.8N 103.8W 19.5N 107.2W 19.9N 111.2W 20.1N 115.9W

    LBAR 18.3N 107.6W 22.0N 111.2W 25.7N 113.5W 28.3N 113.3W

    SHIP 65KTS 58KTS 47KTS 40KTS

    DSHP 65KTS 58KTS 47KTS 40KTS



    ...INITIAL CONDITIONS...

    LATCUR = 14.6N LONCUR = 101.3W DIRCUR = 270DEG SPDCUR = 8KT

    LATM12 = 14.6N LONM12 = 99.8W DIRM12 = 265DEG SPDM12 = 6KT

    LATM24 = 14.8N LONM24 = 98.8W

    WNDCUR = 30KT RMAXWD = 45NM WNDM12 = 25KT

    CENPRS = 1002MB OUTPRS = 1006MB OUTRAD = 150NM SDEPTH = M

    RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM



    $$

    NNNN
    Member Since: July 15, 2006 Posts: 176 Comments: 55665
    21/1745 UTC 14.6N 101.4W T2.5/2.5 93E--East Pacific
    Member Since: Posts: Comments:
    Quoting Ossqss:


    That was at 11:15am and yesterdays was at 10am.

    Here is what it is now from WU for Bradenton. The humidity has dropped along with the dewpoint.
    93.4 °F
    Clear
    Humidity: 19%
    Dew Point: 45 °F


    Bradenton WU link

    I would begin to question the readings...current WU bradenton has dewpoint at 47, here in Boynton, dewpoint is 77, Tampa is 77 and Orlando is 71. Obviously that is the determining factor in the heat index.
    Member Since: Posts: Comments:
    well in any wish way this TD has a better ch of being the 1st name storm
    Member Since: Posts: Comments:
    Quoting extreme236:


    It just has to do with the environment it is in.



    oh
    Member Since: Posts: Comments:
    Quoting pottery:
    Interesting points on the low SAL and the high water temps,( positives) and the high sheer.(negative)
    But beer in mind, so far in the Atl, there has not been a really decent wave to put matters to the test, as yet.


    Is that some sort of typo excuse, or something? (j/k) Not that you had one in this post...
    Member Since: August 16, 2007 Posts: 6 Comments: 12463
    Quoting Tazmanian:
    dont you think 1002mb is a little low for olny a 30kt TD???


    It just has to do with the environment it is in.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    SHIPS guidance is showing moderate shear taking hold on TD 2E within the next 24 hours, apparently offset by the 30+ degree celsius waters I would assume, as strengthening is forecast.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    dont you think 1002mb is a little low for olny a 30kt TD???
    Member Since: Posts: Comments:
    Quoting nrtiwlnvragn:


    ATCF


    thank you
    Member Since: August 2, 2007 Posts: 19 Comments: 19234
    Quoting nrtiwlnvragn:


    ATCF



    thank you
    Member Since: Posts: Comments:
    i think this has a better CH of becomeing the 1st name storm and may be the 1st hurricane
    Member Since: Posts: Comments:
    Quoting extreme236:


    Could i get the link to that site? I lost it when I switched computers.


    ATCF
    Member Since: Posts: Comments:
    Quoting extreme236:


    Could i get the link to that site? I lost it when I switched computers.



    same here i like the link too
    Member Since: Posts: Comments:
    we now have TD 2E


    000
    WHXX01 KMIA 211826
    CHGE77
    TROPICAL CYCLONE GUIDANCE MESSAGE
    NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
    1826 UTC SUN JUN 21 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

    DISTURBANCE TWO (EP022009) 20090621 1800 UTC

    ...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
    090621 1800 090622 0600 090622 1800 090623 0600

    LAT LON LAT LON LAT LON LAT LON
    BAMS 14.6N 101.3W 15.1N 101.5W 15.9N 101.7W 16.7N 102.2W
    BAMD 14.6N 101.3W 14.8N 101.9W 15.4N 102.5W 16.3N 103.5W
    BAMM 14.6N 101.3W 14.9N 101.7W 15.7N 102.0W 16.7N 102.6W
    LBAR 14.6N 101.3W 15.1N 102.4W 15.8N 103.9W 16.9N 105.7W
    SHIP 30KTS 38KTS 49KTS 57KTS
    DSHP 30KTS 38KTS 49KTS 57KTS

    ...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
    090623 1800 090624 1800 090625 1800 090626 1800

    LAT LON LAT LON LAT LON LAT LON
    BAMS 17.7N 103.2W 19.1N 105.6W 19.6N 108.2W 20.3N 111.8W
    BAMD 17.4N 105.0W 19.0N 109.0W 19.9N 113.6W 20.2N 118.3W
    BAMM 17.8N 103.8W 19.5N 107.2W 19.9N 111.2W 20.1N 115.9W
    LBAR 18.3N 107.6W 22.0N 111.2W 25.7N 113.5W 28.3N 113.3W
    SHIP 65KTS 58KTS 47KTS 40KTS
    DSHP 65KTS 58KTS 47KTS 40KTS

    ...INITIAL CONDITIONS...
    LATCUR = 14.6N LONCUR = 101.3W DIRCUR = 270DEG SPDCUR = 8KT
    LATM12 = 14.6N LONM12 = 99.8W DIRM12 = 265DEG SPDM12 = 6KT
    LATM24 = 14.8N LONM24 = 98.8W
    WNDCUR = 30KT RMAXWD = 45NM WNDM12 = 25KT
    CENPRS = 1002MB OUTPRS = 1006MB OUTRAD = 150NM SDEPTH = M
    RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM
    Member Since: Posts: Comments:
    Quoting nrtiwlnvragn:
    invest_RENUMBER_ep932009_ep022009.ren


    Could i get the link to that site? I lost it when I switched computers.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234


    5-Day SST change.

    Warming of SST's in the tropical EPAC has slowed significantly, and Atlantic warming is now outpacing it. A positive ENSO event may no longer be a foregone conclusion.
    Member Since: Posts: Comments:
    invest_RENUMBER_ep932009_ep022009.ren
    Member Since: Posts: Comments:
    Quoting IpswichWeatherCenter:


    To me - its not that well organised.

    Hasn't quite got the convection on all fronts.


    You don't have to have that. Its got strong centralized convection and spiral convective bands. Looks like an inner core circulation is forming as well.
    Member Since: August 2, 2007 Posts: 19 Comments: 19234


    humidex 86.1 its warm and getting warmer
    Member Since: July 15, 2006 Posts: 176 Comments: 55665

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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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