Intense New England Hurricanes Much More Numerous 340 to 1800 Years Ago

By: Jeff Masters , 6:43 PM GMT on February 17, 2015

Numerous Category 3 and 4 hurricanes frequently pounded New England during the first millennium, from the peak of the Roman Empire into the height of the Middle Ages, said a study accepted for publication this month in the open-access journal Earth’s Future, Climate Forcing of Unprecedented Intense-Hurricane Activity in the Last 2,000 Years. These prehistoric hurricanes were stronger than any hurricane documented to hit the region since the mid-1800s, and would be catastrophic if they hit the region today, according to Jeff Donnelly, a scientist at Woods Hole Oceanographic Institution (WHOI) in Massachusetts and lead author of the new paper. In a press release, Donnelly said, “We hope this study broadens our sense of what is possible and what we should expect in a warmer climate. We may need to begin planning for a category 3 hurricane landfall every decade or so rather than every 100 or 200 years.”


Figure 1. The storm surge from Category 2 Hurricane Carol in 1954 batters New England's Edgewood Yacht Club near Providence, Rhode Island. Image credit: NOAA Photo Library.

The paper is the latest contribution to the field of paleotempestology--the study of past tropical cyclone activity by means sediment deposits, cave speleothems, tree rings, coral deposits, as well as historical documentary records. In this case, the researchers took sediment cores from Salt Pond near Falmouth on Cape Cod, Massachusetts. The pond is separated from the ocean by a 1.3- to 1.8-meter (4.3- to 5.9-foot) high sand barrier. Over hundreds of years, storm surges from Category 2 and stronger hurricanes have deposited sediment over the barrier and into the pond. The scientists were able to calibrate the timing of the intense hurricane strikes by dating the layers from Category 2 Hurricane Bob of 1991, the 1675 (September 7) New England hurricane, and the Great Colonial Hurricane of 1635, which passed across southeastern New England and caused widespread damage consistent with a category 3 hurricane.


Figure 2. Scientists collect a sediment core from Salt Pond in Falmouth, Massachusetts, to study hurricane overwash deposits placed there by storm surges from intense hurricanes. The aluminum tube was vibrated into the muddy sediment at the bottom of the pond and then extracted with a hoist. Image Credit: WHOI

The prehistoric sediments showed that there were two periods of elevated intense hurricane activity on Cape Cod--from 150 to 1150, and from 1400 to 1675. Previous paleotempestology studies also found evidence of high hurricane activity during 150 - 1150 A.D. from the Caribbean to the Gulf Coast. Both time periods had unusually warm sea surface temperatures (SSTs) in the Main Development Region for hurricanes, from the Caribbean to the coast of Africa. Warm ocean temperatures in this region have been linked to increased intense hurricane activity by a number of recent research papers. In recent decades, ocean temperatures in the Main Development Region have surpassed the warmth of prehistoric levels, and these waters are expected to warm further over the next century as the climate heats up, suggesting that intense hurricane activity in New England may return to the levels of 340 to 1800 years ago. However, other factors besides warming SSTs will also shape what happens in the North Atlantic. For example, the pattern of ocean warming could bring more El Niño-style wind shear to the Atlantic, reducing hurricane activity. Still, New England would be wise to take heed of Donnelly's advice that we may need to begin planning for a category 3 hurricane landfall every decade or so rather than every 100 or 200 years.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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Quoting 229. ClimateChange:



I don't know. It seemed like in past blocking episodes it didn't get all that cold. Was mostly hype. But something changed last winter and this winter. We're seeing record cold. That shouldn't be possible with today's globally warmed atmosphere.

it is happening
its cold air displacement from abnormal jet patterns
and warm areas over the high north warmer waters under the ice
causing air too find new colder areas to settle into
trying to establish new cold core regions

maybe just a guess
its climate change and every region on the globe
is experiencing changes to there patterns
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Quoting 226. LAbonbon:

It's time for me to turn in. Spent some time tonight reading through recent daily blogs from the Mount Washington Observatory. Had no idea this existed - pretty neat.

Night, all.
You had no idea this existed? Good night indeed Shamus!
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Quoting 229. ClimateChange:



I don't know. It seemed like in past blocking episodes it didn't get all that cold. Was mostly hype. But something changed last winter and this winter. We're seeing record cold. That shouldn't be possible with today's globally warmed atmosphere.



With a highly amplified jet stream due to a blocking high over Cali, it's unusually warm (and dry) out west and pretty cold in the eastern half of the country.
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233. beell
Quoting 221. PedleyCA:



So, that makes me Southern and those in Canoga Park are Northern, too funny...


Sorry,Ped. It don't count. You're left coast.
:)
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Quoting 201. sar2401:

That's one reason you'll never understand the South. The War of Northern Aggression is only one name for that unpleasantness. There's the War for Southern Independence, the War of Separation, the Second Revolution, the War for Southern Rights, The Yankee Invasion, The Lost Cause. There are more but you get the picture. I'm only a Southerner by adoption but I understand the effect the war had on the South, and especially the aftermath. Down here, the war will live on forever.
Those names are hogwash, basically the South can not accept they fought a war in order to preserve slavery so they make up a bunch of crap to play the victim because they cant accept the terrible things they did. Not that the north has a perfect human rights record, but sure as hell more so than the south.
calling me ignorant based off your gross misrepresentation of history is utterly insane.
Just incase if there was any question of what "Rights" the south was "protecting"
from the SC Declaration of Secession
"Those States have assumed the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of Slavery"
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Quoting 229. ClimateChange:



I don't know. It seemed like in past blocking episodes it didn't get all that cold. Was mostly hype. But something changed last winter and this winter. We're seeing record cold. That shouldn't be possible with today's globally warmed atmosphere.


Why shouldn't it be possible? Cold air is still cold, this is a displacement of cold air spilling into areas it normally isn't.
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Quoting 223. KEEPEROFTHEGATE:

sorry ped you were blue as per 1861 map


I would not go by that map for 1 second. In New York, Connecticut, Vermont, Massachusetts, New Hampshire, and especially Maine, they are called Bootsies, and live right outside of every town. Quite derogatory.
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Quoting 130. ColoradoBob1:

I would remind everyone Dr. Jennifer Francis is right. This deep loop in the jet stream has been in place for weeks .
It has been stuck for weeks, And it is exactly what she forecast.


I don't know. It seemed like in past blocking episodes it didn't get all that cold. Was mostly hype. But something changed last winter and this winter. We're seeing record cold. That shouldn't be possible with today's globally warmed atmosphere.
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Quoting 224. Chucktown:

Say it ain't so, it got to 45 degrees in Alaska in February of 1920. I blame it on faulty equipment, maybe a little heat island effect mixed in for good measure.

Per NWS Anchorage twitter today:

@NWSAnchorage: Missed it by that much. Today's high in #Anchorage reached 44º... 45º was the record set in 1920. #AKwx #Alaska


I would "blame" it on the temperature of the air, after all Anchorage is warming at the rate of about 1.18 C per century, but then again I'm not into perpetuating conspiracy theories about faulty equipment and UHI since those things are checked and adjusted for.


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I'm stealing Patrap's thunder here, but let's get back on topic. Crikey, there's a cyclone in Australia mates. G'day!
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It's time for me to turn in. Spent some time tonight reading through recent daily blogs from the Mount Washington Observatory. Had no idea this existed - pretty neat.

Night, all.
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Quoting 201. sar2401:

That's one reason you'll never understand the South. The War of Northern Aggression is only one name for that unpleasantness. There's the War for Southern Independence, the War of Separation, the Second Revolution, the War for Southern Rights, The Yankee Invasion, The Lost Cause. There are more but you get the picture. I'm only a Southerner by adoption but I understand the effect the war had on the South, and especially the aftermath. Down here, the war will live on forever.
Doesn't have to if we teach history in schools again. I am Eastern First American, which means for all I know my tribal village is under some building in downtown D.C. We fought on both sides of that battle after the battles with the Pilgrim, Jesuit, Spanish, French, British, Portuguese sailors? It was so confusing then that scholars still can't figure it out. The weather did not help either. I am still able to give you traditional native weather views based upon 3 principles. (1) Someone kicked someone's ass. (2) Someone was good looking. [3] Someone was a good diplomat. [4] Was lucky.
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Say it ain't so, it got to 45 degrees in Alaska in February of 1920. I blame it on faulty equipment, maybe a little heat island effect mixed in for good measure.

Per NWS Anchorage twitter today:

@NWSAnchorage: Missed it by that much. Today's high in #Anchorage reached 44º... 45º was the record set in 1920. #AKwx #Alaska
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Quoting 221. PedleyCA:



So, that makes me Southern and those in Canoga Park are Northern, too funny...
sorry ped you were blue as per 1861 map

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Quoting 165. aquak9:

anything north of I-10 is "northern".

Preach it, Brutha Beell! Preach it!

Can I get an AMEN??


So, that makes me Southern and those in Canoga Park are Northern, too funny...
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Quoting 205. sar2401:

The South is easily defined. There are only 11 states that qualify -

South Carolina
Mississippi
Florida
Alabama
Georgia
Louisiana
Texas
Virginia
Arkansas
North Carolina
Tennessee

These are the states of the Confederacy. There no other Southern states. There are other states in the south, but it's not the same.


are you sure florida counts??? i know its swamp land but i am not so sure :)
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Quoting 185. sar2401:

No, I don't think I am with Bob. The study makes it pretty clear that only a storm with the path of Bob and at least the strength of Bob is going to lay down enough material for the cores to find it. According to the authors, even the 1938 hurricane, at 180 kilometers to the west, wasn't strong enough to leave a depositional layer, but Bob, although weaker, at 100 kilometers west, was. That makes Bob a pretty important guy. It's kind of like me saying I'm going to study prehistoric hurricanes on the Gulf Coast but whatever my equipment is only sensitive enough to detect at least a cat 2 and it has to make landfall within 100 km east of Mobile Bay. Actually, it would have to be right in the middle of Mobile Bay. No, too far over...that might raise a few questions, I think.

Yes, I think Donnelly's statement quoted in the blog qualifies as pure hyperbole. It will get him lots of quotes. However, it's also going to get a lot of questions from people who do read studies - like me. Is that what we want? How about we have two abstracts. One can be for all the scientists. The other can be for the non-scientists. Look, Naga, you're a sociologist. Read the paragraph you quoted from the study in #150. Even though you're a "soft" science guy who gets hooted at by all the "hard" science guys, you've learned a lot about their game. Do you think there's any chance in God's green earth that you could rewrite that paragraph in a way that one of the pickup truck guys down here might actually understand it? This is not a battle for science. Except for exactly what will happen and when, the science behind global warming is pretty clear to those who would understand. This is a battle for hearts and minds, and we can't win it by being obtuse. If the guys who did the study can't write in clear expositional English, send it out to someone like you that can. And for heavens sake, zip your lip when you're about to go overboard. :-)



Ok, last statement about Bob...Bob is great because they can only look for Bob's in this location using this method. They aren't looking for all systems, or even some systems, they are looking for guys who look like Bob because it's the only thing they can look for with any accuracy using this specific method at this specific location, they weren't trying to generalize and state as much.

Now on to the meat...I reject the soft versus hard science thing. That's something people like to say to separate themselves from guys like me when we start talking about institutions, structures, power, etc., I like to remind them our methods are based in the same conceptual framework only what we study is different. I think the soft / hard science thing died out awhile ago anyways, I don't hear it much anymore. Besides, my checks and my diplomas say College of Sciences on them same as the "hard" science guys.

You aren't going to like my response about rewriting that paragraph, yes I could rewrite it to make it more readable and understandable to the average person, but I don't think it's the publication itself's job to do it. Journal articles are written in a specific way, it's a discourse between scientists not a communication to the masses. Don't get me wrong, I think there needs to be better communication of studies, but I don't think that comes from changing the wording and stylistic flair within academic writing. I think that comes from removing the sensationalism that comes with reporting on science. I think scientists should stop making hyperreal comments designed to be attention grabbers and not literally correct. I think it would be good if there were scientists/journalists who were trustworthy interpreters to the general public and that scientific research still was regarded as holding privilege in informational creation. Heck, I might even go as far as to argue that a second copy written in more clear language should be made for communicative purposes, but for lack of a better term "dumbing down" academic writing is not the way to go.

Reforming the system would break the system. We are taught to write in certain ways because we are judged in peer review by others who have been taught to write that way and worse, we teach new people to write that way because if they don't the old guard won't publish them. It's completely tautological nonsense, but it's the way it works, and changing it would mean a complete reworking of the system and these ivory towers aren't coming down anytime soon.

Besides my two skills in life are sociology and being able to read journal level articles...what would I do if you took away one of my niches? :)
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Quoting 201. sar2401:

That's one reason you'll never understand the South. The War of Northern Aggression is only one name for that unpleasantness. There's the War for Southern Independence, the War of Separation, the Second Revolution, the War for Southern Rights, The Yankee Invasion, The Lost Cause. There are more but you get the picture. I'm only a Southerner by adoption but I understand the effect the war had on the South, and especially the aftermath. Down here, the war will live on forever.
ya but now you all live as one

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Quoting 211. Pallis1:

Just protection against perpetrating carpetbaggers and foul weather. It actually works both ways. When you go up North, there is a good ole' boy system to drive you back home. ESA’s Swarm mission should clear up boundaries, hopefully.

Not sure I should ask, Pallis, but what's the ESA Swarm mission?
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Quoting 215. KEEPEROFTHEGATE:

lets see what the second post says

If you ran a pool I think I could clean up
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Quoting 214. LAbonbon:

#206 - not a very nice first post
lets see what the second post says
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#206 - not a very nice first post
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I wish. I could. Make really. Pithy comments.

But I can't, darn it. :-)
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Quoting 160. LAbonbon:


LOL - my thoughts exactly. When I lived in New England, I considered VA to be the South, and some people considered MD to be. Now that I live in South Louisiana, I no longer really view VA or even perhaps TN as the South. I know people that would not include Arkansas or North Carolina, either, and have heard people from these states referred to as yankees :)

Kind of blew my mind at first. It's all relative...
Just protection against perpetrating carpetbaggers and foul weather. It actually works both ways. When you go up North, there is a good ole' boy system to drive you back home. ESA’s Swarm mission should clear up boundaries, hopefully.
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Quoting 206. DarrellD:

Complete BS.
Lol.Wha?
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Quoting 186. ScottLincoln:


I have not read much about the paper in question but have seen some of the discussion on it.

With regards to average recurrence interval (ARI), a relatively modern term I prefer over the similar terms "return period" or "return interval", there are a few things that people frequently misunderstand.
1) The value corresponds to a long term average, and should not be used as some sort of expectation of when an event will occur. Comments like "we are overdue" are not warranted when discussing an ARI; one needs to look at the underlying physical mechanisms which will provide better information to use in forecasting events.
2) The majority of the time something is assigned a "return period" or ARI, the chance of occurance is independent, or near independent, from surrounding years. So just because you had a "100 year" (1% chance) flood last year doesn't mean that you chance is reduced this year.
3) The most extreme (most rare) part of an event is often very isolated and not experienced by the vast majority of persons who think that they experienced it. Here's an example to illustrate. Summer, 1993, in the midwest. Most of the state of Iowa experienced heavy rainfall and most rivers experienced decent river rises. A few locations, on a few rivers, had conditions that were classified as "100-year" or greater events. Probably 10% or fewer people actually experienced flooding of that magnitude (the 100 year or 500 year in the hardest hit areas) but many will calibrate to the event as if they had experienced such an event. Not to say that they didn't experience flooding, but they didn't experience the 100 year or greater. Another example: see Fig 10 in this paper. That event was a particularly significant event for the southeast Louisiana and southern Mississippi area and almost everyone in the area recalls it and discusses how bad it was. Yet if you look at the rainfall ARI analysis, only small portions of 3 counties experienced 1000-year (0.1% chance) event and most events I've studied have a much smaller spatial coverage of the maximum.

Does any of that help?



Actually, Scott - I'm aware of these points. I appreciate you taking the time and posting them, and for sharing your paper :P

The discussion in the paper is not nearly so straightforward as your summary just was. They discuss it in sections 2.6 (Methods) and 3.1.3 (Results). Here is 3.1.3:

"3.1.3 Changes in event frequency
The Salt Pond record indicates considerable changes in the frequency of event beds over the
last 2000 years, with historically unprecedented intervals of event-bed deposition. A total of
thirty-five event layers were deposited over the last 2000 years (Figs. 2a and 3a); the highest
frequencies were reached at 1420-1675 CE (10 event beds, #2-11) and 150-1150 CE (23
event beds, #13-35). Assuming hurricane landfall occurrence follows a Poisson process we
can estimate the probability of exceeding the number of events expected by random chance
alone. For example, using 0.9 events per century as the expected rate (λ) (derived from the
162-year NOAA Best Track Dataset, Supplementary Fig. 4), the probability of experiencing three or more events in any one century is 0.06 (6%). Several intervals in the 4th to 7th centuries, 11th century, and 15th to early 17th centuries exceed this frequency (Fig. 3a). The
probability of experiencing one or more events in any one century is 0.6 (60%). However, the
probability of experiencing ten consecutive centuries with one or more events per century, as
recorded at Salt Pond between ca. 150 and 1150 CE, is quite low at 0.006 (0.6%). Similarly,
the probability of experiencing two or more events in two consecutive centuries, as
reconstructed in Salt Pond between ca. 1440 and 1640 CE (Fig. 3a), is only 0.04 (4%), and in
fact event bed frequency exceeds three events per century through most of this interval.
Hence, compared to modern event frequencies in the region, significant portions of the 2,000
year Salt Pond record exceed what would be expected based on random event occurrence
alone."

The original question was, where did the 'decade' comment come from? I made a stab/guess at it in an earlier post, but would love to hear your thoughts, if you have time to read the study. If not, no worries :)
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Quoting TimTheWxMan:



The civil war battles are named differently too. For example, southerners call the Battle of Bull Run the Battle of Manassas.
Yes, and the Merrimac, of Monitor and Merrimac fame, is the CSS Virginia. That kind of thing is touchy down here.
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maybe more snow in the northeast on wednesday night
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Quoting TimTheWxMan:



The South could also be defined based on their political leanings too. They're also heavily religious.
The South is easily defined. There are only 11 states that qualify -

South Carolina
Mississippi
Florida
Alabama
Georgia
Louisiana
Texas
Virginia
Arkansas
North Carolina
Tennessee

These are the states of the Confederacy. There no other Southern states. There are other states in the south, but it's not the same.
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Quoting 201. sar2401:

That's one reason you'll never understand the South. The War of Northern Aggression is only one name for that unpleasantness. There's the War for Southern Independence, the War of Separation, the Second Revolution, the War for Southern Rights, The Yankee Invasion, The Lost Cause. There are more but you get the picture. I'm only a Southerner by adoption but I understand the effect the war had on the South, and especially the aftermath. Down here, the war will live on forever.



The civil war battles are named differently too. For example, southerners call the Battle of Bull Run the Battle of Manassas.
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Quoting ColoradoBob1:
Every great empire from the past is a scam. That's is why we all suffer, we are kings now.
Seriously, can you pass some of that around instead of hogging it all yourself...
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Quoting 159. KEEPEROFTHEGATE:







The South could also be defined based on their political leanings too. They're also heavily religious.
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Quoting Methurricanes:
I stopped reading after War of. Northern Aggression.
That's one reason you'll never understand the South. The War of Northern Aggression is only one name for that unpleasantness. There's the War for Southern Independence, the War of Separation, the Second Revolution, the War for Southern Rights, The Yankee Invasion, The Lost Cause. There are more but you get the picture. I'm only a Southerner by adoption but I understand the effect the war had on the South, and especially the aftermath. Down here, the war will live on forever.
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SPECTACULAR SWEDISH LIGHT SHOW
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Quoting 196. ColoradoBob1:

Every great empire from the past is a scam. That's is why we all suffer, we are kings now.



Uhhh.... what?
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Quoting 196. ColoradoBob1:

Every great empire from the past is a scam. That's is why we all suffer, we are kings now.
Wow, ok (walks quickly away)
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Quoting 160. LAbonbon:


LOL - my thoughts exactly. When I lived in New England, I considered VA to be the South, and some people considered MD to be. Now that I live in South Louisiana, I no longer really view VA or even perhaps TN as the South. I know people that would not include Arkansas or North Carolina, either, and have heard people from these states referred to as yankees :)

Kind of blew my mind at first. It's all relative...



One of my geography books puts St. Louis and Pittsburgh as part of the "inland south". Ah shure don't sound lak a sutherner... y'all.
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Every great empire from the past is a scam. That's is why we all suffer, we are kings now.
Member Since: December 31, 1969 Posts: Comments:
Quoting 180. BaltimoreBrian:

Poll: Which Native American symbol for hurricane is better?

The Maya



Or the Taino of Cuba?



I like the Taino symbol better.



The Taino one's better.
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ScottLincoln which symbol for hurricane do you like better? Since you're a meteorologist.
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Quoting 188. sar2401:

Bob, I don't know what you're smoking tonight but it must be terrific! :-)


Well, he is from Colorado so yeah.
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Quoting 190. washingtonian115:

Don't forget the half diamond shape indented land surrounded by most of M.D and some of V.A.
You do know that there are alligators in the rivers now!!! Global swarming.
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Quoting 164. aquak9:

As far as I'm concerned, anyone north of Georgia is a northerner.
-or-
If you get to see snow every 2-4 years.

No-good-closed-shoe-wearin' Yankees, tossin' perfectly good lawn chairs around city streets - -

:)



There's more than one way to define the South. One is their ability (or lack thereof) to handle winter weather and treating one inch of snow like the apocalypse (Atlanta looking like a scene out of the walking dead last year). :O)
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Quoting 181. wxgeek723:



Nah, Maryland is a Northern state in my opinion. It's accustomed to snow, and it's a developed blue state.
Don't forget the half diamond shape indented land surrounded by most of M.D and some of V.A.
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Quoting 180. BaltimoreBrian:

Poll: Which Native American symbol for hurricane is better?

The Maya



Or the Taino of Cuba?



I like the Taino symbol better.
Maya have other symbols for that. Taino is spread out over 1000 miles of influence. Timeline, unknown. Add, subtract coastline at current sea level. Swastika is the first. It was Buddhist thousands of years after Native Americans carved it into rocks. I doubt they called it a Swastika though, because in recent(last 1100 years or so, until present day) we called it the 4 winds.
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Quoting ColoradoBob1:
Every Mayan temple was covered for hundreds of years with a plaster made from limestone, made from the forest around them. You cook limestone to make lime. Lime makes plaster. Wood makes charcoal. Charcoal bakes limestone.

In the beginning this cycle ain't a big deal, but these kings when crazy A cyclone was just a foot note at the end.

These people stuck sting ray barbs in their foreskins to get in touch with the Gods. And their queens did the same thing. You bled on a paper , then you lite it on fire. The smoke would take man's message to the Gods.

Only kings and queens did this. Everyone else cut down trees , and hauled rocks.
Bob, I don't know what you're smoking tonight but it must be terrific! :-)
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Quoting BaltimoreBrian:
Poll: Which Native American symbol for hurricane is better?

The Maya



Or the Taino of Cuba?



I like the Taino symbol better.
Well, Taino looks more like a hurricane, so he'd make a better hieroglyph. The Maya guy looks a lot scarier though. Tough choice...
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Quoting 151. LAbonbon:


Regarding return interval - I don't know where 'decade' comes from, nor do I know where 8/5/3 years comes from. From reading through that section of the paper, and looking at the graphs, there are periods where 4 'intense' storms per century occurred (pre-history), whereas they identified 3 'intense' storms in the last 380 years. There's a discussion of calculated changes in event frequency in Section 3.1.3. Perhaps his 'decade' comment came from the suggestion that identified storms in prehistory could have been stronger than Bob and the 1600s storms, due to the additional distance to transport the coarse sediment...I don't know. *shrugs*

Maybe ScottLincoln or schistkicker can weigh in on the return intervals...


I have not read much about the paper in question but have seen some of the discussion on it.

With regards to average recurrence interval (ARI), a relatively modern term I prefer over the similar terms "return period" or "return interval", there are a few things that people frequently misunderstand.
1) The value corresponds to a long term average, and should not be used as some sort of expectation of when an event will occur. Comments like "we are overdue" are not warranted when discussing an ARI; one needs to look at the underlying physical mechanisms which will provide better information to use in forecasting events.
2) The majority of the time something is assigned a "return period" or ARI, the chance of occurance is independent, or near independent, from surrounding years. So just because you had a "100 year" (1% chance) flood last year doesn't mean that you chance is reduced this year.
3) The most extreme (most rare) part of an event is often very isolated and not experienced by the vast majority of persons who think that they experienced it. Here's an example to illustrate. Summer, 1993, in the midwest. Most of the state of Iowa experienced heavy rainfall and most rivers experienced decent river rises. A few locations, on a few rivers, had conditions that were classified as "100-year" or greater events. Probably 10% or fewer people actually experienced flooding of that magnitude (the 100 year or 500 year in the hardest hit areas) but many will calibrate to the event as if they had experienced such an event. Not to say that they didn't experience flooding, but they didn't experience the 100 year or greater. Another example: see Fig 10 in this paper. That event was a particularly significant event for the southeast Louisiana and southern Mississippi area and almost everyone in the area recalls it and discusses how bad it was. Yet if you look at the rainfall ARI analysis, only small portions of 3 counties experienced 1000-year (0.1% chance) event and most events I've studied have a much smaller spatial coverage of the maximum.

Does any of that help?

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather