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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Is anyone buying the idea of severe weather in florida tomorrow? What is the likelihood of these supposed storms firing up?
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Thanks Jeffs - so looking at those charts, the week of July 8 has the best conditions based on the MJO.

Does the green ever show over the caribbean or only the waves coming off Africa have that?
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391. IKE
Quoting ALCoastGambler:
Ike...New blogger near Dauphin Island. Watched the posts all year last year found them very helpful, from you and all. I am a gulf watcher this time of year not very intelligent on weather but I thiink SST is important. Does it seem high to you this time of year?


South of where we live...yes...water temps near 87 degrees. Not right at the coast though. It's only near 80 at the NW Fl. beaches.
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...SPECIAL FEATURES...

LOW NEAR 15N100W 1005 MB MOVING WEST NORTHWEST 5 KNOTS. BROAD
CYCLONIC TURNING CAN BE SEEN IN A LARGE AREA SURROUNDING THE
SYSTEM. CONVECTION NEAR THE CENTER HAS INCREASED SINCE YESTERDAY
WITH SCATTERED MODERATE TO STRONG CONVECTION WITHIN 180 NM OF
THE POINT 14N102.5W. THE CONVECTION NEAREST THE CENTER IS
ORGANIZING IN A BAND WITHIN 120 NM OF THE SOUTHERN SEMICIRCLE OF
THE CIRCULATION. OTHER AREAS OF CONVECTION WELL EAST OF THE
CENTER ARE ALONG AND OFFSHORE THE COAST FROM WESTERN EL SALVADOR
TO THE GULF OF TEHUANTEPEC WITH SCATTERED MODERATE ISOLATED
STRONG WITHIN 180 NM OF 13N92.5W. HEAVY RAINS ARE LIKELY ALONG
THE COAST AND WILL BE ENHANCED INLAND DUE TO OROGRAPHIC
EFFECTS. UPPER LEVEL OUTFLOW OVER THIS REGION IS PROVIDING AN
ENVIRONMENT FAVORABLE FOR CONTINUED DEEP CONVECTION AND THE LOW
MAY BECOME A TROPICAL CYCLONE IN THE NEXT 24 HOURS.

Member Since: July 15, 2006 Posts: 169 Comments: 53296
Ike...New blogger near Dauphin Island. Watched the posts all year last year found them very helpful, from you and all. I am a gulf watcher this time of year not very intelligent on weather but I thiink SST is important. Does it seem high to you this time of year?
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Quoting jeffs713:

Are we looking at the same map? I just see the wave around 45W getting sheared to smithereens, no spin there. (the low-level clouds look like spots on the water, and the upper-level clouds are thin and wispy). It is pretty apparent that the low-level clouds are slowly drifting west, while the upper-level is getting torn apart to the ENE.


I saw the same thing.... couldnt see a spin anywhere.
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About a mile to my south (note this isn't mine).
Palm Springs, Lake Worth, Florida (PWS)
Updated: 5 min 19 sec ago
Mostly Cloudy
94.3 °F
Mostly Cloudy
Humidity: 59%
Dew Point: 78 °F
Wind: 6.0 mph from the NNW
Wind Gust: 10.0 mph
Pressure: 29.81 in (Falling)
Heat Index: 110 °F
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting stoormfury:
nice spin in atl tropical wave


Link

Are we looking at the same map? I just see the wave around 45W getting sheared to smithereens, no spin there. (the low-level clouds look like spots on the water, and the upper-level clouds are thin and wispy). It is pretty apparent that the low-level clouds are slowly drifting west, while the upper-level is getting torn apart to the ENE.
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Quoting heliluv2trac:
maybe i quoted that incorrectly i should have asked when do you all think conditions should become more favorable for tsd

give it a few weeks. shear is up there right now, and the area of the warmest water (the GOM) is sitting under a ridge of oven-like death. Until the high moves away, the main places for TS formation will be near the bahamas (nothing near there right now to provide a spark, but one may be coming within the week), and in the western caribbean (shear is nasty right now). This year is going pretty much with the average, as June is one of the quietest months of the year for TS formation. July is starts to warm up, and in August, you are cooking with gas. (September you are cooking with a plasma torch or something like that)
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nice spin in atl tropical wave


Link
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Quoting heliluv2trac:
maybe i quoted that incorrectly i should have asked when do you all think conditions should become more favorable for tsd
Probably when we least expect it.
Member Since: October 9, 2008 Posts: 0 Comments: 8266
maybe i quoted that incorrectly i should have asked when do you all think conditions should become more favorable for tsd
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Quoting zoomiami:


Can someone please explain how to interprete this graphic? TIA

Sorry - graphic didn't show, its post 322, the MJO pulse

The orange is a downward pulse (generally supresses storm formation, by inhibiting convection), and green is an upward pulse (generally helps storm formation, by encouraging convection). When you see white inside the green area, that is a VERY strong upward pulse, and greatly helps storm formation by encouraging convection.

A lot of people are watching the MJO since last year's storms worked almost perfectly in tandem with the MJO. When we had an upward pulse, we got a lot of storms forming, and the downward pulses gave us mini-breaks. (Gustav and Ike were both in an upward pulse, as an example)
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Looks like the moisture in the NW Caribbean is being drawn towards 93E.
Member Since: October 9, 2008 Posts: 0 Comments: 8266
thats true storm i just thought maybe the nam or the gfs was picking up on something
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Quoting heliluv2trac:
does anyone have any idea when we will see our first tropical storm

when mother nature says its time.
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81*F dewpoint here in sarasota after the noon hour.....to freaken humid/hot!!!!,dewpoints in the 80's are not common durning the daytime hrs here in the sub-tropical region....
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Definitely a day to stay inside, like an oven out already.
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Quoting heliluv2trac:
does anyone have any idea when we will see our first tropical storm
Only the Almighty could answer that question.
Member Since: October 9, 2008 Posts: 0 Comments: 8266
does anyone have any idea when we will see our first tropical storm
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Quoting Stormchaser2007:
One hell of a pulse on the GFS.



Can someone please explain how to interprete this graphic? TIA

Sorry - graphic didn't show, its post 322, the MJO pulse
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i am ready for some action
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From the Melbourne, FL NWS:


Heat Index readings already dangerously high at 10 am


Heat index readings are already becoming dangerously high as of 10 am, and are expected to top out between 105 and 110 this afternoon.

Persons in east central Florida need to take precautions from the heat.

If heading to the beach to cool off, be aware that rip currents continue to be a danger, and despite relatively calm looking conditions, many rescues have occurred at area beaches in the past few days. Only swim within sight of a lifeguard and never swim alone.


HEAT INDEX READINGS AS OF 10 AM:


Photobucket


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370. IKE
Quoting futuremet:


It looks like you are going to get the dry side Iky.


According to the 12Z NAM I'm not....

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it is 91 here in Port St Lucie FL
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368. IKE
Quoting TheCaneWhisperer:
Pennock Ln., Jupiter, Florida (PWS)
Updated: 9 sec ago
Mostly Cloudy
97.1 °F
Mostly Cloudy
Humidity: 56%
Dew Point: 79 °F
Wind: 3.1 mph from the NW
Wind Gust: 10.4 mph
Pressure: 29.89 in (Falling)
Heat Index: 116 °F
Visibility: 8.0 miles
UV: 10.8 out of 16
Clouds:
Few 2000 ft
Scattered Clouds 6000 ft
Mostly Cloudy 25000 ft
(Above Ground Level)


Yikes.


Good lord that's brutal.
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Pennock Ln., Jupiter, Florida (PWS)
Updated: 9 sec ago
Mostly Cloudy
97.1 °F
Mostly Cloudy
Humidity: 56%
Dew Point: 79 °F
Wind: 3.1 mph from the NW
Wind Gust: 10.4 mph
Pressure: 29.89 in (Falling)
Heat Index: 116 °F
Visibility: 8.0 miles
UV: 10.8 out of 16
Clouds:
Few 2000 ft
Scattered Clouds 6000 ft
Mostly Cloudy 25000 ft
(Above Ground Level)


Yikes.
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heat index 79.6 and risen forecasted high of 80 today with heat index of 85 gets warmer from here on out in mid 80's by wed with heat indexs of 90's or slightly higher
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting AussieStorm:

whats the chance of that making it into the GOM?



none
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Quoting IKE:
GFS 12Z @ 72 hours....1007 mb low near west coast of Florida...



It looks like you are going to get the dry side Iky.
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Looks like a train forming in the WPAC
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there's another invest brewing in the east pac about 800-1000 miles out.....
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Quoting AussieStorm:

would any remnants make it?


I would highly doubt it, that area of Mexico is all Mountains, if it went North. If it follows its present track, then KOG is right... it would have to cross the dessert and Texas to get there .
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Quoting AussieStorm:

whats the chance of that making it into the GOM?
no chance should move n nw may follow previous system into mex/baja then north into desert sw as it disapate
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting Orcasystems:


Ummmm I would guess not much... it would have to cross Mexico to get there.

would any remnants make it?
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357. IKE
GFS 12Z @ 72 hours....1007 mb low near west coast of Florida...

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Quoting AussieStorm:

whats the chance of that making it into the GOM?


Ummmm I would guess not much... it would have to cross Mexico to get there.
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805

NOUS42 KNHC 211430

WEATHER RECONNAISSANCE FLIGHTS

CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.

1030 AM EDT SUN 21 JUNE 2009

SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)

VALID 22/1100Z TO 23/1100Z JUNE 2009

TCPOD NUMBER.....09-024



I. ATLANTIC REQUIREMENTS

1. NEGATIVE RECONNAISSANCE REQUIREMENTS.

2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.



II. PACIFIC REQUIREMENTS

1. NEGATIVE RECONNAISSANCE REQUIREMENTS.

2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.

SEF
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting KEEPEROFTHEGATE:


1. UPDATED...SATELLITE IMAGES INDICATE THAT SHOWERS AND THUNDERSTORMS
ASSOCIATED WITH THE AREA OF LOW PRESSURE CENTERED ABOUT 150 MILES
SOUTHWEST OF ACAPULCO MEXICO CONTINUE TO BECOME BETTER ORGANIZED...
BUT THE LOW-LEVEL CENTER OF CIRCULATION IS NOT YET WELL-DEFINED.
ONLY A SLIGHT INCREASE IN THE ORGANIZATION OF THIS SYSTEM WOULD
RESULT IN THE FORMATION OF A TROPICAL DEPRESSION...AND ADVISORIES
COULD BE INITIATED LATER TODAY. THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS. HEAVY RAINS COULD AFFECT PORTIONS OF THE
SOUTHERN AND SOUTHWESTERN COAST OF MEXICO DURING THE NEXT DAY OR
TWO...AND INTERESTS IN THIS REGION SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.

whats the chance of that making it into the GOM?
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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 hunkerdown:

At what times of the day were the different humidity readings taken ? Dewpoint of 50 seems a little low for yesterday's weather conditions. Current Florida dewpoints are in the upper 70s to low 80s with 60s reaching up to the mid-atlantic.


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
Member Since: June 12, 2005 Posts: 6 Comments: 8185
Anyone want to guess how many more days its going to take to complete the US Open :(
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1. UPDATED...SATELLITE IMAGES INDICATE THAT SHOWERS AND THUNDERSTORMS
ASSOCIATED WITH THE AREA OF LOW PRESSURE CENTERED ABOUT 150 MILES
SOUTHWEST OF ACAPULCO MEXICO CONTINUE TO BECOME BETTER ORGANIZED...
BUT THE LOW-LEVEL CENTER OF CIRCULATION IS NOT YET WELL-DEFINED.
ONLY A SLIGHT INCREASE IN THE ORGANIZATION OF THIS SYSTEM WOULD
RESULT IN THE FORMATION OF A TROPICAL DEPRESSION...AND ADVISORIES
COULD BE INITIATED LATER TODAY. THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS. HEAVY RAINS COULD AFFECT PORTIONS OF THE
SOUTHERN AND SOUTHWESTERN COAST OF MEXICO DURING THE NEXT DAY OR
TWO...AND INTERESTS IN THIS REGION SHOULD MONITOR THE PROGRESS OF
THIS SYSTEM.
Member Since: July 15, 2006 Posts: 169 Comments: 53296
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dvorak estimates have it a 2.0,which is 35mph,TD for sure!!!
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793

WHXX04 KWBC 210523

CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL DEPRESSION INVEST 93E



INITIAL TIME 0Z JUN 21



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 14.7 98.8 360./ .0

6 15.3 99.6 309./ 9.3

12 15.6 100.0 305./ 5.7

18 15.8 100.6 288./ 5.5

24 16.0 101.2 287./ 6.2

30 16.1 102.1 281./ 9.3

36 16.4 102.8 294./ 6.9

42 16.4 103.7 269./ 8.5

48 16.6 103.1 75./ 5.7

54 17.1 103.1 2./ 4.9

60 17.8 103.4 333./ 7.9

66 18.2 104.1 306./ 7.9

72 19.0 105.1 306./11.8

78 20.9 106.1 333./21.5

84 21.8 106.4 339./ 9.3

90 22.3 107.1 304./ 7.9

96 23.5 108.5 311./17.5

102 23.8 109.2 293./ 7.2

108 23.9 110.1 276./ 8.2

114 23.9 110.9 275./ 7.2

120 24.4 112.0 294./11.2

126 24.6 112.6 282./ 5.8
Member Since: July 15, 2006 Posts: 169 Comments: 53296
CHGE77

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

1222 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 INVEST (EP932009) 20090621 1200 UTC



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

090621 1200 090622 0000 090622 1200 090623 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 14.7N 100.3W 15.0N 100.7W 15.6N 101.2W 16.3N 101.7W

BAMD 14.7N 100.3W 14.9N 101.0W 15.4N 101.8W 16.2N 102.6W

BAMM 14.7N 100.3W 15.1N 100.9W 15.6N 101.5W 16.4N 102.2W

LBAR 14.7N 100.3W 15.2N 101.3W 15.8N 102.6W 16.9N 104.2W

SHIP 25KTS 30KTS 38KTS 47KTS

DSHP 25KTS 30KTS 38KTS 47KTS



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

090623 1200 090624 1200 090625 1200 090626 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 17.1N 102.5W 18.7N 104.8W 19.0N 107.5W 19.5N 111.3W

BAMD 17.2N 103.9W 18.9N 107.5W 19.5N 112.1W 19.8N 117.4W

BAMM 17.3N 103.3W 19.0N 106.4W 19.3N 110.4W 19.5N 115.4W

LBAR 18.2N 106.0W 21.7N 109.7W 24.9N 112.7W 27.5N 114.2W

SHIP 56KTS 64KTS 59KTS 53KTS

DSHP 56KTS 64KTS 59KTS 53KTS
Member Since: July 15, 2006 Posts: 169 Comments: 53296

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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.