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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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???

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1543. Levi32
Thanks for helping to explain it Storm.
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1541. gator23
Quoting Chicklit:
Thanks, Hurricane.
I'm going to go read a book.


Read Gods Other Son by Don Imus so that you and Vortfix can get along. (July 10)

Link
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1540. Levi32
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


It sure didn't materialize much did it. Apparently the region of instability was too far to the east.
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Thanks, Hurricane.
I'm going to go read a book.
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1537. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 163 Comments: 52257
Quoting Levi32:


I think it's ridiculous that after all this they're still saying "El Nino MAY come"...."El Nino Watch issued"....."50% chance of El Nino this year".

Come on guys.....El Nino is already here.

Thanks for the article Taz.
Quoting Levi32:


I think it's ridiculous that after all this they're still saying "El Nino MAY come"...."El Nino Watch issued"....."50% chance of El Nino this year".

Come on guys.....El Nino is already here.

Thanks for the article Taz.



your welcome
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1535. vortfix
We are fortunate to have amongst us several certified Meteorologists who we can learn a lot from.


N0...there's none of those on here either.

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1534. gator23
Quoting Chicklit:
vortfix, i don't know what's buggin you but i suggest you turn off your computer and find out. man, you have a chip on your shoulder the size of the empire state building.
if you have nothing to contribute to the conversation then shut up.


he is just upset Imus (July 10) was fired.
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vortfix, i don't know what's buggin you but i suggest you turn off your computer and find out. man, you have a chip on your shoulder the size of the empire state building.
if you have nothing to contribute to the conversation then shut up.
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1532. gator23
Quoting Levi32:


Ok well all I want to say is that certainly nobody has to listen (July 10)to anything I say. I'm not a certified Meteorologist, but most people on this blog aren't. We are fortunate to have amongst us several certified Meteorologists who we can learn a lot from.


As far as im (July 10) concerned no one on here "knows" whats going on. its weather we can only guess. If people want to post advisories i say great (July 10) at least the advisory will have better guesses (July 10) than mine and 80 percent of the WU bloggers.
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1531. Levi32
Quoting vortfix:
Nah Chicklit.
I don't think there's a rude report on the WU.
I am not being rude...I just know what I'm talking about!
Maybe you would rather listen to 17 year old tropical "Experts" who live in Alaska!

Report that!



Ok well all I want to say is that certainly nobody has to listen to anything I say. I'm not a certified Meteorologist, but most people on this blog aren't. We are fortunate to have amongst us several certified Meteorologists who we can learn a lot from. And for official information consult the NHC and NWS offices. That's why I posted the advisories in the firstest place.
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Quoting vortfix:
Nah Chicklit.
I don't think there's a rude report on the WU.
I am not being rude...I just know what I'm talking about!
Maybe you would rather listen to 17 year old tropical "Experts" who live in Alaska!

Report that!



LOL.......dido
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1528. KEEPEROFTHEGATE (Mod)


02E/H/C1/A

BEARING NNW SHIFTING WNW
TRACK ALONG NORTHERN EDGE ALBATROSS PLATEAU 90 TO 100 MILES OFFSHORE

Member Since: July 15, 2006 Posts: 163 Comments: 52257
1527. gator23
Quoting hurricane2009:
Question

since when is it being bored or a bad thing to post advisories for tropical systems? Even if they arent in the Atlantic.

Can someone enlighten me on this one?


July 10th
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1525. Levi32
Quoting Chicklit:
It is what I understand as the downward MJO. Where is the Caribbean, Florida, The Gulf.


Ok that's the MJO upward-motion pulse that is bringing upward motion and therefore increased moisture to the east Pacific and the areas you mentioned. That's not a high pressure area though; it actually creates lower surface pressures because of the rising air.

Since air flows towards low pressure, westerlies from the west are very welcomed and received warmly in the east Pacific lol. The downward air motion in the west Pacific and Indian Ocean forces air to spread out at the ocean surface, causing it to travel eastward, and then it gets sucked back up into the atmosphere by the low pressure in the east Pacific.
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vortfix, i think you're about to be reported for being rude.
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It is what I understand as the downward MJO in the Caribbean, Florida, The Gulf. Is this totally wrong?
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1521. Levi32
Quoting Chicklit:
What do you call it, Levi?


I don't know if I don't know what ridge lol :P

What's going through my mind right now is that there are no semi-permanent ridges in the equatorial Pacific, which is why I am not sure what you're talking about.

Where is the ridge you're talking about located?
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What do you call it, Levi?
I know very little about the technical side.
I watch cloud formations and try to follow along with the technical conversations.
Just throwing my two cents in.
Enlighten me please.
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1518. Levi32
Quoting Chicklit:

It's a little El Nino though. The ridge will hold back westerlies if it stays put, won't it?


What ridge do you mean?

Yeah it's in its infancy right now but it will be growing up as we get into the fall and probably peak during winter. I don't think this will be a multi-year event.
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Quoting Levi32:


I think it's ridiculous that after all this they're still saying "El Nino MAY come"...."El Nino Watch issued"....."50% chance of El Nino this year".

Come on guys.....El Nino is already here.

Thanks for the article Taz.

It's a little El Nino though. The ridge will hold back westerlies if it stays put, won't it?
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My family and I are taking a 7-day cruise from Galveston to Key West and the Bahamas from July 12-19th.

Hopefully we see some interesting weather develop... nothing nasty, just interesting.

Been on two Carribean cruises in August before... but no tropical storms, hurricanes or any interesting weather. Nothing but nice, pleasant Carribean atmosphere.

Hopeful that nothing hits Houston while were not home. :>)
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Quoting stillwaiting:



part of the mjo pulse moving into the southern GOM????

...not the mojo pulse again!
that always makes for trouble.
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(((02E ANDRES)))
CI# /Pressure/ Vmax
4.2 / 986.1mb/ 69.8kt


Final T# Adj T# Raw T#
(3hr avg)
4.1 4.0 4.0

Latitude bias adjustment to MSLP : +2.3mb

Center Temp : -78.6C Cloud Region Temp : -74.8C

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
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1512. Levi32
Quoting Tazmanian:
whats do you guys think hmmmmm


Link


I think it's ridiculous that after all this they're still saying "El Nino MAY come"...."El Nino Watch issued"....."50% chance of El Nino this year".

Come on guys.....El Nino is already here.

Thanks for the article Taz.
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whats do you guys think hmmmmm


Link
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1510. beell
You're killin' me, Levi lol!
We'll see
)
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1509. Levi32
Quoting vortfix:
OMG...you people are posting advisories and discussions!

If it's that boring...please go play video games!



Spoken from the advisory-posting master lol, and I don't play video games =P
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Link

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1505. vortfix
OMG...you people are posting advisories and discussions!

If it's that boring...please go play video games!

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1504. Levi32
Quoting beell:
Levi! Look! a trough split we can agree on!
j/k

The 500mb 18Z at 36hrs


I hate to break it to you beell....but if you're looking at the 500mb circulation over Panama, that circulation is pre-existing and is not a split piece from the trough lol. The real trough-split takes place a day or two after that. You can see it in the image below in the Bay of Campeche where it will have moved into by that time. Grrr and here I wanted so much to agree that we agree! lol =)

GFS 500mb 96 hours:

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1464. H23

The 2nd area is the Bermuda ridge which is displaced farther to the EAST now, meaning 'recurve' potential is high for the next 6 weeks or so.


Valid points but steering patterns this far out? seems like throwing darts at a board to me who knows what will happen until we get to those months.
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Sharp wind shifts but light winds across the BOC

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1501. beell
Levi! Look! a trough split we can agree on!
j/k

The 500mb 18Z at 36hrs
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Quoting WAHA:

Too late; Noel did that in 2007, and I seriously doubt that Karen would take a toll on this system.

The remnants of Karen, now that is a clever and funny remark. I remember all that talk!
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1499. Levi32
000
WTPZ42 KNHC 230241
TCDEP2
TROPICAL STORM ANDRES DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022009
800 PM PDT MON JUN 22 2009

VISIBLE AND INFRARED SATELLITE IMAGERY INDICATES THAT ANDRES
CONTINUES TO SLOWLY BUT STEADILY DEVELOP...WITH THE CENTER EMBEDDED
WITHIN A CENTRAL DENSE OVERCAST. EARLIER TRMM AND AMSU-B PASSES
ALSO INDICATE WELL-DEFINED BANDING FEATURES AND THE POSSIBLE
FORMATION OF A PARTIAL EYEWALL. 0000 UTC T-NUMBERS FROM TAFB AND
SAB ARE BOTH 3.5 AND ARE USED TO SET THE INITIAL INTENSITY AT 55
KT.

THE BEST ESTIMATE OF THE INITIAL MOTION IS 315/7. WATER VAPOR IMAGES
AND CLOUD-TRACKED WINDS SHOW A LARGE AND STRONG SUBTROPICAL RIDGE
EXTENDING FROM THE CENTRAL U.S. SOUTHWESTWARD THROUGH NORTHERN
MEXICO...WITH A DEEP-LAYER TROUGH OFFSHORE THE CALIFORNIA COAST.
ANDRES' CURRENT NORTHWESTWARD HEADING...FORECAST REASONABLY WELL BY
SEVERAL TRACK MODELS...APPEARS TO BE IN RESPONSE TO A WEAKNESS IN
THE SUBTROPICAL RIDGE OVER WESTERN MEXICO. HOWEVER...GLOBAL MODELS
SHOW THE RIDGE BUILDING WESTWARD OVER THE NEXT COUPLE OF
DAYS ...WHICH SHOULD STEER ANDRES MORE TOWARD THE WEST...BUT NOT
BEFORE IT NEARS THE SOUTHWESTERN COAST OF MEXICO ON TUESDAY. THE
OFFICIAL FORECAST IS SLOWER THAN THE MODEL CONSENSUS BUT SLIGHTLY
FASTER THAN THE PREVIOUS OFFICIAL FORECAST.

THE SHIPS MODEL CONTINUES TO SHOW NEARLY 20 KT OF NORTHEAST TO EAST
SHEAR OVER ANDRES AND MOST OF THE RELIABLE GLOBAL MODELS WEAKEN THE
CYCLONE IN ABOUT A DAY OR TWO. HOWEVER...GIVEN THE CURRENT UPWARD
INTENSITY TREND AND THE WARM SSTS ALONG ITS TRACK...A CONTINUED BUT
GRADUAL INTENSIFICATION THROUGH ABOUT 36 HOURS IS ANTICIPATED.
ANDRES IS FORECAST TO REACH HURRICANE STRENGTH WITHIN 12 HOURS BUT
SHOULD REACH COOLER WATERS AND BEGIN INGESTING STABLE AIR IN ABOUT
36 HOURS...RESULTING IN A MORE RAPID DECREASE IN STRENGTH. IT
SHOULD BE MENTIONED THAT...IF ANDRES MOVES TO THE RIGHT OF THE
FORECAST TRACK...IT COULD INTERACT MORE SIGNIFICANTLY WITH LAND AND
WEAKEN FASTER.


FORECAST POSITIONS AND MAX WINDS

INITIAL 23/0300Z 16.8N 103.1W 55 KT
12HR VT 23/1200Z 17.8N 104.0W 65 KT
24HR VT 24/0000Z 19.2N 105.6W 65 KT
36HR VT 24/1200Z 20.5N 107.0W 65 KT
48HR VT 25/0000Z 21.0N 108.5W 55 KT
72HR VT 26/0000Z 21.5N 111.0W 45 KT
96HR VT 27/0000Z 22.0N 114.0W 35 KT
120HR VT 28/0000Z 22.0N 118.0W 25 KT...REMNANT LOW

$$
FORECASTER KIMBERLAIN/AVILA


That last paragraph there is perfect forecast reasoning, which I have come to expect from Avila.
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There is definitely potential for this to strengthen quite a bit if it can stay away from land.

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1497. Ossqss
For those of you that forgot. Pertains to us all, one way or another.

L8R .......

Dad's day, day late
Member Since: June 12, 2005 Posts: 6 Comments: 8183
1495. Levi32
000
WTPZ32 KNHC 230241
TCPEP2
BULLETIN
TROPICAL STORM ANDRES ADVISORY NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022009
800 PM PDT MON JUN 22 2009

...ANDRES GRADUALLY STRENGTHENING...

A HURRICANE WARNING REMAINS IN EFFECT FOR THE SOUTHWESTERN COAST OF
MEXICO FROM PUNTO SAN TELMO TO CABO CORRIENTES. A HURRICANE WARNING
MEANS THAT HURRICANE CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE
WARNING AREA WITHIN 24 HOURS. PREPARATIONS TO PROTECT LIFE AND
PROPERTY SHOULD BE RUSHED TO COMPLETION.

A TROPICAL STORM WARNING AND A HURRICANE WATCH REMAIN IN EFFECT FOR
THE SOUTHWESTERN COAST OF MEXICO FROM LAZARO CARDENAS TO PUNTO SAN
TELMO. A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM
CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 24
HOURS. A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE ALONG THE SOUTHWESTERN COAST OF MEXICO SHOULD
MONITOR THE PROGRESS OF ANDRES.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL STORM ANDRES WAS
LOCATED NEAR LATITUDE 16.8 NORTH...LONGITUDE 103.1 WEST OR ABOUT 100
MILES...165 KM...SOUTHWEST OF LAZARO CARDENAS MEXICO AND ABOUT 170
MILES...275 KM...SOUTH-SOUTHEAST OF MANZANILLO MEXICO.

ANDRES IS MOVING TOWARD THE NORTHWEST NEAR 8 MPH...13 KM/HR...AND
THIS MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 TO 36 HOURS WITH
A SLIGHT INCREASE IN FORWARD SPEED. ON THE FORECAST TRACK... ANDRES
SHOULD PASS VERY CLOSE TO THE SOUTHWESTERN COAST OF MEXICO WITHIN
THE WARNING AREA ON TUESDAY.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO 65 MPH...100 KM/HR...WITH
HIGHER GUSTS. ANDRES IS FORECAST TO BECOME A HURRICANE ON TUESDAY.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB...29.35 INCHES.

ANDRES IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF 4 TO 8
INCHES OVER PORTIONS OF WEST-CENTRAL MEXICO...WITH POSSIBLE ISOLATED
MAXIMUM AMOUNTS OF 12 INCHES.

COASTAL STORM SURGE FLOODING OF 1 TO 3 FEET ABOVE NORMAL TIDE
LEVELS...ALONG WITH LARGE AND DANGEROUS BATTERING WAVES...ARE
POSSIBLE AS ANDRES MOVES CLOSE TO THE WARNING AREA.

...SUMMARY OF 800 PM PDT INFORMATION...
LOCATION...16.8N 103.1W
MAXIMUM SUSTAINED WINDS...65 MPH
PRESENT MOVEMENT...NORTHWEST OR 315 DEGREES AT 8 MPH
MINIMUM CENTRAL PRESSURE...994 MB

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 1100 PM PDT FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 200
AM PDT.

$$
FORECASTER KIMBERLAIN/AVILA

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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:

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.