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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294. IKE
Quoting presslord:
Portlight Party and Performance in Houston today...lottsa WU folks there...we'vve sorta come full circle...good times and great fellowship, I'm sure...


Will you be there in your hot dress?
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Portlight Party and Performance in Houston today...lottsa WU folks there...we'vve sorta come full circle...good times and great fellowship, I'm sure...
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Ike hit Inagua, Bahamas, the southern most island in the Bahamas. Also the home of the only wild Flamingo colony left in the Bahamas. Most of the Flamingos left, but some were found dead in the mangroves. A week after the storm the rest returned.

I had just worked a Spay/Neuter clinic there that spring. It's a beautiful island with the nicest people I have met from any of the Bahamian islands! I was sick watching Ike make a bee line for them and then trying to find out how they faired. They did better than expected, no human deaths and not many animal deaths either.
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Quoting AussieStorm:

I see what u mean.....


It's only a disturbance, there's no isobars clusters around that.
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Good Morning;

Summer Is Here!; Tropical Update; Other Stuff
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting WxLogic:
Good Morning...

We should start seeing interesting WX features developing this upcoming week all the way from the W Carib to the Mid Atl. NOGAPS has been rather persistant at developing a strong disturb region in the W Carib in response to the upward MJO this upcoming week but no model support yet from the others. So we'll have to see.

I see what u mean.....
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Good Morning...

We should start seeing interesting WX features developing this upcoming week all the way from the W Carib to the Mid Atl. NOGAPS has been rather persistant at developing a strong disturb region in the W Carib in response to the upward MJO this upcoming week but no model support yet from the others. So we'll have to see.
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Has anyone seen the last 2 NOGAPS? I think its sending a ts or cane to Fl. Not an expert on models but looks like something. Have a good day all. Happy Fathers Day.
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Good morning all.
The TPC is quite bullish this morning regarding possible surface low spin-up near the Bahamas mid-week:



MARINE WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
100 AM EDT SUN JUN 21 2009

MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN SEA
AND SOUTHWEST NORTH ATLC S OF 31N W OF 55W.

ATLC...
A POTENT SHORTWAVE TROUGH OVER THE MID-ATLANTIC STATES CONTINUES
TO QUICKLY DIVE SOUTHEASTWARD OFF THE E COAST. AN UPPER LEVEL
JET MAXIMUM DIVING TOWARD THE UPPER TROUGH AXIS WILL CONTINUE
AMPLIFYING IT OFF THE E COAST THROUGH EARLY NEXT WEEK.
MEANWHILE...A DEEPENING SURFACE LOW WILL CONTINUE MOVING SE OFF
THE E COAST...WITH A WEAKENING COLD FRONT ENTERING THE NORTHERN
WATERS ON MON. AS THE AFOREMENTIONED UPPER TROUGH CUTS OFF FROM
UPPER LEVEL JET SUPPORT EARLY NEXT WEEK...THE SURFACE FRONT WILL
WEAKEN ON MON...LEAVING BEHIND A TRAILING SURFACE TROUGH OVER
THE SW NORTH ATLC. ALL AVAILABLE GLOBAL MODEL GUIDANCE SUGGESTS
A SERIES OF MID-LEVEL VORT LOBES PIVOTING CYCLONICALLY AROUND
THE DEEP LOW N OF THE AREA. THE MOST SIGNIFICANT OF THESE WILL
DIVE SOUTHEASTWARD INTO THE SW NORTH ATLC EARLY MONDAY. DEEP
LAYER LIFT AHEAD OF THIS WAVE WILL BE MORE THAN SUFFICIENT TO
SPIN UP A SURFACE LOW ALONG THE TROUGH SOMEWHERE ACROSS THE SW
NORTH ATLC BY MON AFTERNOON...MOST LIKELY NE OF THE BAHAMAS.
MODELS HAVE BEEN TRENDING WITH A DEEPER LOW...POTENTIALLY IN
RESPONSE TO ANY REMNANT WEAK THERMAL GRADIENTS ACROSS THE
BOUNDARY. BY MON EVENING...THE GFS...ECMWF...UKMET...AND NAM ALL
CARRY A SURFACE LOW IN THE 1000-1003 MB RANGE WITHIN 90 NM OF
29N73W ALONG THE SURFACE TROUGH. HIGH CONFIDENCE EXISTS IN A
SWATH OF SW WINDS OF 20 TO 30 KT BETWEEN THE SURFACE TROUGH AND
THE SUBTROPICAL RIDGE. HOWEVER...IT IS LIKELY THAT THESE WINDS
WILL BE LOCALLY ENHANCED TO GALE FORCE IN THE E SEMICIRCLE OF
THE LOW DUE TO THE STEEPENED PRESSURE GRADIENT. THIS GRADIENT
WILL BE FURTHER ENHANCED AS THE SUBTROPICAL RIDGE SHIFTS
WESTWARD IN RESPONSE TO AMPLIFICATION AND RETROGRESSION OF THE
CORRESPONDING CENTRAL ATLC MID-LEVEL RIDGE. A LARGE SUITE OF
AVAILABLE GUIDANCE SUGGESTS THE LIKELIHOOD FOR GALES EMBEDDED
WITHIN THE LARGER WIND SWATH ON TUESDAY...AND THIS SEEMS
ENTIRELY REASONABLE GIVEN THE DEEPER INSTABILITY UNDER THE UPPER
TROUGH PROMOTING GREATER MIXING...ESPECIALLY WITH SEA SURFACE
TEMPERATURES SLIGHTLY ABOVE AVERAGE IN THE 26-27 DEG CELSIUS
RANGE. THE THREAT FOR GALES WILL LIFT N OF THE DISCUSSION AREA
BY TUE EVENING...WHILE THE SWATH OF SW WINDS AT 20-30 KT
CONTINUES E OF THE SURFACE TROUGH INTO THU.


ALSO...A TROPICAL WAVE EXTENDING FROM 11N47W TO 7N49W TO 3N50W
IS FORECAST TO MOVE WESTWARD AT 10-12 KT DURING THE NEXT FEW
DAYS. THIS WAVE IS SHOWING SOME SIGNS OF AMPLIFICATION...THOUGH
SOUTHERN PORTIONS OF THE WAVE WILL LIKELY WEAKEN THEY INTERACTS
WITH HIGHER TERRAIN OVER NORTHERN PORTIONS OF SOUTH AMERICA.

CARIBBEAN...
NE TO E E WINDS OF 15 TO 20 KT COVER MUCH OF THE CARIBBEAN AT
PRESENT...WITH THE STRONGEST WINDS OF 20 TO 25 KT FOUND NEAR THE
COAST OF COLOMBIA. THE HIGHEST SEAS OF 8 TO 10 FT WILL ALSO BE
FOUND NEAR THE COAST OF COLOMBIA. THE AFOREMENTIONED TROPICAL
WAVE WILL MOVE INTO THE EASTERN CARIBBEAN TUE. AT THE SAME
TIME...THE DEEPENING SURFACE TROUGH OVER THE SW NORTH ATLC WILL
VEER WINDS OVER THE E CARIBBEAN TO MORE SOUTHEASTERLY EARLY NEXT
WEEK...WITH THE REMNANTS OF THE TROPICAL WAVE BEING STEERED
NORTHWESTWARD AS IT MOVES ACROSS THE CARIBBEAN NEXT WEEK. WEAKER
LOW LEVEL FLOW NEAR THE BROAD SURFACE TROUGH WILL SLOW THE
WAVE/S MOTION BY THE MIDDLE OF NEXT WEEK. A BUILDING SUBTROPICAL
RIDGE OVER THE CENTRAL ATLC WILL MAINTAIN MODERATE TO FRESH
TRADE WINDS ACROSS THE E CARIBBEAN NEXT WEEK.

GULF OF MEXICO...
SURFACE HIGH PRES OVER THE N CENTRAL GULF WILL AFFECT MUCH OF
THE GULF INTO EARLY NEXT WEEK...WHILE DRIFTING WESTWARD. THIS
WILL STEEPEN THE PRESSURE GRADIENT BETWEEN THE HIGH AND A BROAD
TROUGH OVER MEXICO TO DRIVE E TO SE WINDS UP TO 20 KT ACROSS THE
BAY OF CAMPECHE FOR THE MIDDLE OF NEXT WEEK. ALSO...ACROSS THE E
GULF...WINDS WILL BECOME NW AT 15 TO 20 KT NEXT WEEK IN RESPONSE
TO THE DEEPENING LAYER LOW IN THE WESTERN N ATLC.




48 Hour Surface Forecast:

Photobucket

Member Since: October 29, 2007 Posts: 135 Comments: 46068
good morning
the tropical atlantic is the same refrain. Troughiness and high vertical wind shear. although the wind shear tendency is for a drop in the shear in the gomex and carib, there are no threat ares to talk about this morning. The models are not hinting of tropical development for the next seven days. it is beginning to appear that we may not get a named storm in the atlantic this month
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93E is doing well!


When do you think we will get classification?
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goodnight (July 10th)
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280. jsker
Quoting charlottefl:
Was just wondering if anyone saw this:




I made a post about 7 hours ago asking the same question and no one seamed intrested. what are you thoughts
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Was just wondering if anyone saw this:


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Quoting Stormchaser2007:
The craziest TCHP I have ever seen in the Atlantic.


That's absolutely insane. It is no wonder Wilma was able to explosively deepen to become the strongest Atlantic hurricane on record.
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The craziest TCHP I have ever seen in the Atlantic.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Quoting hurricane2009:


2008 had 3 Category 4's

Gustav, Ike and Paloma


Omar was upgraded post season to Category 4 status.
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Quoting Tazmanian:



they one hurricane was a there where 3 cat 2 hurricanes and olny one of them wish was the G storm that had 150mph winds that made land fall some where but i dont re call any cat 4s makeing land fall any where other then that G storm


Ike did on an Island (Forgot which)
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Im also starting to think this season will be similar to 2002 with the El Nino event. But that's not good, 2002 was a rough year even though they had 12 named storms.
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Quoting CybrTeddy:
2008 had 4 Category 4's,
all four of them effected land at that intensity.



they one hurricane was a there where 3 cat 2 hurricanes and olny one of them wish was the G storm that had 150mph winds that made land fall some where but i dont re call any cat 4s makeing land fall any where other then that G storm
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2008 had 4 Category 4's,
all four of them effected land at that intensity.
2007 was the only season that featured 2 Category 5's making landfall at Category 5 status.
2005 you know was insane with the Category 4 storms.
2004 Charley, Frances, Ivan all effected land at Category 4 intensity.
2003 Isabel was the only Atlantic Category 5 so far this decade. The rest were all GOMEX and Caribbean Canes. Fabian also made landfall at Bermuda at Category 4 intensity.
2002 featured Hurricane Lili as a Category 4.
2001 featured Iris and Michelle.
2000 Featured Keith and Issac. Issac never effected land.
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269. Dr3w
Quoting hurricane2009:


Its possible, guess we will see

by the way 1999 had a record 5 Category 4 hurricanes


how many of those cat 4's hit land?
dont for get El Nino is comein to play this year
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Quoting hurricane2009:
well here is an interesting thought, with the except of the Cape Verde Season, could this year be similar to 1999?

We only had 1 named storm and a short lived depression up until mid-August, ended up with 12 named storms and several were strong


I don't like to have to keep mentioning 2004 but the first storm didn't form until unusually late.
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This should validate Jeff Masters research:
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Quoting hurricane2009:
well here is an interesting thought, with the except of the Cape Verde Season, could this year be similar to 1999?

We only had 1 named storm and a short lived depression up until mid-August, ended up with 12 named storms and several were strong


Why rule out a Cape Verde season? SAL should be low, and CV's don't get crankin until late August anyway.
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Quoting Drakoen:


You could use the build of of SSTs as an analogy. SSTs support stronger storms that consume the energy built up in the ocean once the heat potential is transferred into kinetic energy the storm can use there is a depletion in the potential energy until it can be regained again.


Well said. Obviously there is much more at play, but where is the quantifiable threshold? We still don't know until we see the Sat/Quicksat. That's not good enough. We need to make it better! and can. Night all.----
Member Since: June 12, 2005 Posts: 6 Comments: 8185
This is for all the people of Winnie and Anahuac...Bridge City and the Bolivar Penninsula...Billy Bad Bird...and all the people with disabilities in metro Houston and Galveston... as we come full circle this weekend...

And for all the people whose heartfelt response gave peace and comfort.


They who sailed the sea in ships, trading on the deep waters, these saw the works of the Lord and His wonders in the abyss.

His command raised up a storm wind which tossed its waves on high. They mounted up to Heaven; they sank to the depths; their hearts melted away in their plight.

They cried to the Lord in their distress: from their straights He rescued them, He hushed the storm to a gentle breeze, and the billows of the sea were stilled.

They rejoiced that they were calmed, and He brought them to their desired haven. Let them give thanks to the Lord for his kindness and His wonderous deeds to the children of men.

Psalm 107
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Quoting Ossqss:
Agreed, but ------

Root question is, at what point does the total energy absorbed, in a given area, require exhausting by virtue of weather? Sooner or later we get atmospheric TNT /


You could use the build of of SSTs as an analogy. SSTs support stronger storms that consume the energy built up in the ocean once the heat potential is transferred into kinetic energy the storm can use there is a depletion in the potential energy until it can be regained again.
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Quoting hurricane2009:


Yea could be a classic mid latitude development


It just looks like the most interesting thing I've seen in the Atlantic in weeks lol
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well its time to get some sleep
see every one in the morning
iam out
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Agreed, but ------

Root question is, at what point does the total energy absorbed, in a given area, require exhausting by virtue of weather? Sooner or later we get atmospheric TNT /
Member Since: June 12, 2005 Posts: 6 Comments: 8185
Quoting Ossqss:



Should we get some Trough syrup? :)


What is your take Drak,the heat is pumping up and something has to give ?

The Earth needs to vent, right?



A little dry on the jokes... lol!

Looks like we will get somewhat of a cool down as the trough sets up of the east coast.
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Blob watch between 35 to 40 N and 70W
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Quoting Drakoen:
Upper level troughing dominates the Atlantic Basin.



Should we get some Trough syrup? :)


What is your take Drak,the heat is pumping up and something has to give ?

The Earth needs to vent, right?

Member Since: June 12, 2005 Posts: 6 Comments: 8185
Upper level troughing dominates the Atlantic Basin.
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249. IKE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
935 PM EDT SAT JUN 20 2009

...A HEAT ADVISORY REMAINS IN EFFECT FOR SOUTHEAST ALABAMA...
SOUTHWEST AND SOUTH CENTRAL GEORGIA AS WELL AS THE EASTERN FLORIDA
PANHANDLE AND FLORIDA BIG BEND FROM 1 PM EDT (NOON CDT) SUNDAY
AFTERNOON UNTIL 8 PM EDT (7 PM CDT) SUNDAY EVENING...

.UPDATE...OUTSIDE OF A FEW MINOR TWEAKS IN THE GRIDS...NO MAJOR
UPDATES ARE NEEDED THIS EVENING. TEMPERATURES MANAGED TO REACH
THE CENTURY MARK FOR THE FIFTH CONSECUTIVE DAY HERE IN TALLAHASSEE
AND RANGED FROM 96 NEAR THE COAST TO 103 AT TALLAHASSEE. DOTHAN
WAS THE SECOND HIGHEST ACROSS THE LOCAL AREA AT 102 DEGREES.
APALACHICOLA DID TIE THE OLD RECORD THAT WAS SET IN 1998 AT 98
DEGREES TODAY. OUTSIDE OF THE HEAT AND A FEW STORMS SOUTH OF DIXIE
COUNTY EARLIER...THINGS REMAINED VERY QUIET ACROSS MUCH OF THE
REGION THIS AFTERNOON AND EVENING. EXPECT THESE CONDITIONS TO
CONTINUE INTO THE OVERNIGHT HOURS TONIGHT WITH LOWS ONLY DROPPING
TO THE MID 70S INLAND AND ONLY DOWN TO AROUND 80 AT THE COAST.
SUNDAY WILL BE VERY SIMILAR TO THE PAST FEW DAYS WITH TEMPERATURES
EXPECTED TO REACH 100 TO 102. THEREFORE...THE HEAT ADVISORY WILL
CONTINUE FOR SUNDAY AFTERNOON.
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200mb Vorticity
- North Atlantic - Latest Available - Large Scale
Member Since: October 1, 2007 Posts: 81 Comments: 26511
217
218
How do you lose ice, and get colder at the same time? Salt on the ice - just like when making ice cream. (salt or something else that depresses the freezing point) Maybe something on the dust?
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Quoting Rodek:
Anyone ever see strange things get carried in by Hurricanes? While living in Ft Walton Beach a short while ago, we saw birds that were carried in by some storms!!!


I read that birds will get caught in the eye of a storm and ride for hundreds of miles. They become so exhausted they just fall out of the sky where the eye passes. Some storm chasers driving down a deserted I-10 during Rita told how they were just falling everywhere. It is strange. :( poor birdies.

The weirdest thing we found from a hurricane was a broken fishing pole amd someones bait bucket. Lol. Dont know where they came from but Ike left em in the front yard.
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Ripe is the word for sure, evenin.

Interesting seeing the diving dry air heading south over the eastern side of NA into the Atl.

Member Since: June 12, 2005 Posts: 6 Comments: 8185
244. IKE
I've got 83.8 degrees at 9:50 pm in Defuniak Springs,FL.
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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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