97L a major rainfall threat; October hurricane outlook; NC rains finally end

By: Dr. Jeff Masters , 2:08 PM GMT on October 01, 2010

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A large and complex region of disturbed weather (Invest 97L), centered about 800 miles east of the Lesser Antilles Islands, is headed west-northwest at 15 - 20 mph and will bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands on Saturday and Sunday. Wind shear is a moderate 5 - 15 knots over 97L, and the waters beneath are very warm, 29°C. However, recent satellite imagery shows that the intensity and areal coverage of 97L's heavy thunderstorms have decreased this morning, thanks to some dry air being ingested into the storm. The SHIPS model predicts that wind shear over 97L will rise to the high range, 20 - 30 knots, Saturday through Tuesday, but some of the global computer models depict only moderate amounts of shear for 97L during this period. The NOGAPS model is the only model currently showing significant development 97L, and that model predicts 97L will be near Puerto Rico on Monday, the Dominican Republic on Tuesday, Haiti on Wednesday, and Eastern Cuba and the southeast Bahamas on Thursday. NHC is giving 97L a 40% chance of developing into a tropical depression by Sunday, but as of this morning, had not tasked the Hurricane Hunters to fly into the storm over the next two days. 97L will slow down to 5 - 10 mph on Sunday, bringing the potential for an extended 3 - 4 day period of heavy rains for the islands in its path. Even if 97L does not develop into a tropical depression, its slow motion may result in life-threatening flash flooding and mudslides in Puerto Rico, the Dominican Republic, Haiti, and eastern Cuba next week.


Figure 1. Morning satellite image of Invest 97L.

October hurricane outlook
October is here, and it is time to take stock of where we stand and how far we have to go before hurricane season is over. The beginning of October traditionally marks the two-thirds point of hurricane season; approximately one-third of all hurricanes and 28% of named storms occur after October 1. Tropical Storm Nicole brought us up to fourteen named storms for the year, and I expect about 4 - 5 more named storms this year with 2 - 3 of these being hurricanes. That would add up to 18 - 19 named storms for the season, putting 2010 in 3rd - 5th place all-time for most named storms. Since record keeping began in 1851, only four seasons have finished with more than eighteen named storms. These seasons were 2005 (28 named storms, with the 17th named storm, Rita, occurring by October 1); 1933 (21 named storms, with the 18th named storm occurring by October 1;) 1995 (19 named storms, with the 15th named storm, Opal, occurring by October 1;) and 1887 (19 named storms, with the 10th named storm occurring by October 1.) The most likely time to get activity is during the first two weeks of October. There are still two weeks of peak hurricane season left before the activity traditionally begins to decline steeply (Figure 2.) Given the record warm sea surface temperatures in the Atlantic this fall, the presence of La Niña in the Eastern Pacific keeping wind shear lower than average, and the observed increase in late-season activity in recent decades, I expect this year's peak portion of hurricane season will last until the end of October. I predict three named storms, two hurricanes, and one intense hurricane will form in the Atlantic this month, with two named storms and one hurricane occurring in November - December, making 2010 as the third busiest Atlantic hurricane season of all-time.


Figure 2. Climatological frequency of Atlantic named storms and hurricanes.

Jamaica cleans up after Nicole
Tropical Storm Nicole lasted only six hours as a tropical storm, but the storm's torrential rains hit Jamaica hard. Nicole's rains killed at least six people on the island, and at least thirteens others are missing and feared dead. The storm cut power to 170,000 island residents, and caused millions of dollars in damages. Wunderground member JamaicaZed wrote me to say his rain gauge in the Kingston suburb of Norbrook caught 17.39" of rain Monday through Thursday, with 11.10" coming on Wednesday.

Historic rainfall event for eastern North Carolina ends
The rains have finally ended In North Carolina, where tropical moisture streaming northward in advance of Nicole generated a historic rainfall event this week. Wilmington, NC set records this week for the heaviest 3-day, 4-day, and 5-day rainfall events in city history, and the month of September ended up as the second rainiest month ever recorded in the city. A remarkable 22.54" of rain fell on Wilmington during the 5-day period Sunday through Thursday. The previous record was 19.06", set in September 1999 during Hurricane Floyd. Fortunately, eastern North Carolina was under moderate drought conditions prior to this week's rainfall onslaught, with just 0.18" of rain falling during the first 25 days of September. Only minor to moderate flooding is occurring on North Carolina rivers, with just one river, the Northeast Cape Fear River near Chinquapin, expected to experience major flooding. Portlight.org is beginning to identify needs in Eastern North Carolina in the wake of the flooding, and expects to perform the first deployment of their new relief trailer within the next few days and send a truck loaded with water, food and personal hygiene supplies.

The most remarkable thing about Wilmington's second-wettest month in history is that it came without a hurricane affecting North Carolina. All four of the other top-five wettest Septembers in history were due, in large part, to hurricanes:

#1 23.41 inches 1999 (Hurricanes Dennis and Floyd)
#2 22.72 inches 2010 (plume of tropical moisture in advance of TS Nicole)
#3 20.10 inches 1877 (Hurricane Four)
#4 18.94 inches 1984 (Hurricane Diana)
#5 16.93 inches 1924 (Hurricane Five and Tropical Storm Eight)


Figure 3. Radar-estimated precipitation for North Carolina since Sunday shows that the precursor moisture from Nicole has brought widespread rain amounts of fifteen inches (white colors.)

Heavy rains and flooding for New England
The plume of tropical moisture that affected North Carolina is now triggering heavy rains in New England, and flood warnings are posted throughout most of New Jersey, eastern Pennsylvania, eastern New York, Delaware, and Vermont this morning. In New York City, heavy rains this morning have overwhelmed one section of the city's subway system, and flooding closed several key road arteries in the city, snarling the morning commute. About two inches of rain have fallen so far this morning in the city. Severe weather is not expected, and no tornadoes were reported yesterday in association with this weather system.

Elsewhere in the tropics
Disturbed weather continues in the Central Caribbean, where the remnants of Tropical Storm Nicole will bring isolated heavy rain showers today to Hispaniola, Jamaica, Cuba, the Cayman Islands, and northern Honduras. The GFS model predicts this activity will concentrate near Hispaniola over the weekend, then push northwards into the Bahamas, with a subtropical or extratropical storm forming over the Bahamas on Sunday or Monday. This storm could bring 2 - 4 inches of rain to the Bahamas Sunday and Monday. The storm will then move north-northeastwards, parallel to the U.S. East Coast, and not affect any other land areas. Several of the models are predicting the formation of a tropical depression in the Mid-Atlantic 5 - 7 days from now, in a location that would not be of any danger to land areas.

Next update
I'll have an update Saturday morning.

Jeff Masters

Flooding (jdwagon)
Shannon Hills, Ridgeway, VA
Flooding
()

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Season 2010 - GOES East Animation: June - July

This GOES East Infrared Hurricane Sector animation is a long loop that shows all of June and July 2010. This video features Hurricane Alex, which blew up quickly and torched the Mexico Gulf coast and well inland! Also shown is Tropical Storm Bonnie, which could not quite get it together. This video features the music of Gustav Holtz's symphony - "The Planets."



Season 2010 - GOES East Animation: August - September

This GOES East Infrared Hurricane Sector animation is a long loop that shows all of August and September 2010. This video features a slew of tropical storms and hurricanes, none of which made official landfall along the U.S. coastline. How many can you correctly identify? This is one killer video you will want to see again and again. This video features the music of Gustav Holtz's symphony - "The Planets."

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Quoting clubjuggle:

If this is the two-thirds point, shouldn't we be expecting seven more named storms, since 14 is 2/3 of 21?


The 2/3 reference was to time. Since storms are not evenly distributed through the season, but rather have a peak with less active periods at the beginning or the end, this is right.

IMO, the season is over for a lot of folks already, particularly the northern GOM.

Edit to add:

Wow!

Member Since: June 16, 2003 Posts: 0 Comments: 0

I believe you have just claimed the lurking record by a pretty fair margin. XD (Contrats)
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From Dr. Masters:

"October is here, and it is time to take stock of where we stand and how far we have to go before hurricane season is over. The beginning of October traditionally marks the two-thirds point of hurricane season; approximately one-third of all named storms and hurricanes in the Atlantic season occur after October 1. Tropical Storm Nicole brought us up to fourteen named storms for the year, so we should expect about four more named storms this year with one or two of these being hurricanes."

If this is the two-thirds point, shouldn't we be expecting seven more named storms, since 14 is 2/3 of 21?
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63. afj3
Quoting Neapolitan:


The simplest way to look at it is this: all tropical cyclones "want" to go poleward (north in the northern hemisphere). Once steering currents relax enough to allow a storm moving westward with the trade winds to finally follow its instincts, it'll make a turn (that is, a curve) to the right/north. However, once far enough north, the trade winds will cede control to the westerlies, which will generally alter the storm's natural northward movement and force it back toward the east or northeast...thereby giving it its second curve, or "recurve".

(A storm that starts out by moving north and then northeast, as often happens in the fall months, can't properly be said to recurve; it's merely turning eastward. By the same token, a storm that moves only westward then northward isn't recurving, either.)

There. Suitably confused? :-)

Thanks! It
Quoting Neapolitan:


The simplest way to look at it is this: all tropical cyclones "want" to go poleward (north in the northern hemisphere). Once steering currents relax enough to allow a storm moving westward with the trade winds to finally follow its instincts, it'll make a turn (that is, a curve) to the right/north. However, once far enough north, the trade winds will cede control to the westerlies, which will generally alter the storm's natural northward movement and force it back toward the east or northeast...thereby giving it its second curve, or "recurve".

(A storm that starts out by moving north and then northeast, as often happens in the fall months, can't properly be said to recurve; it's merely turning eastward. By the same token, a storm that moves only westward then northward isn't recurving, either.)

There. Suitably confused? :-)


Got it! I knew there was a reason...
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Quoting Thaale:

That may be the oral tradition or something, but storm histories suggest a completion factor closer to three-quarters or four fifths as of October 1:

% of season's storms forming by Oct 1:

All Tropical Storms: 1995-2009: 75%
1980-2009: 77%
1951-2000: 79%

Hurricanes: 1995-2009: 77%
1980-2009: 74%
1951-2000: 76%


Looks like your projection acknowledges as much even if the text doesn't or else you'd probably be projecting an additional 7 or so storms to go with the 14 we've had.

One other point: there may be too few La Nina years on record to make this meanimngful, but La Nina years have generally had earlier peaks and smaller tails than other years. The CW of course is the opposite, but storm history does not support the idea of a La Nina season being expected to have a late peak or a long tail.
Are you getting that from HURDAT yourself, or is there something written you can point to concerning that point?

Not doubting. Good post, which I find interesting and want to look further into...
Member Since: August 16, 2007 Posts: 6 Comments: 12461

Conditions at 42057 as of
(10:50 am EDT)
1450 GMT on 10/01/2010:
Unit of Measure: Time Zone:
Click on the graph icon in the table below to see a time series plot of the last five days of that observation.

Wind Direction (WDIR): W ( 260 deg true )
Wind Speed (WSPD): 13.6 kts
Wind Gust (GST): 15.5 kts
Wave Height (WVHT): 3.0 ft
Dominant Wave Period (DPD): 6 sec
Average Period (APD): 4.4 sec
Atmospheric Pressure (PRES): 29.82 in
Pressure Tendency (PTDY): +0.01 in ( Rising )
Air Temperature (ATMP): 80.1 °F
Water Temperature (WTMP): 84.6 °F
Dew Point (DEWP): 75.6 °F
Heat Index (HEAT): 85.3 °F
Combined plot of Wind Speed, Gust, and Air Pressure
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While SST's are high under 97 the TCHP is not.
Probably why the convection is diminishing and the thunderstorms collapsing to the east




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Well, guess with the current movement 97L will miss the islands. At least some rain. Don't expect surf Mr. PuertoRico... 40mph winds or less can only do so much =P
Member Since: August 3, 2006 Posts: 0 Comments: 2639
Quoting Neapolitan:


That's a great photo (from Mike Meadows)--but you forgot to point out the helicopter inside the rainbow. I lived in SoCal for a long time, and CG lightning in September, while not unheard of, is pretty rare. Excellent.

More images here


I lived in the Mojave desert for awhile and once in awhile there would be HUGE Electrical storms in the distance that we would watch from the hills at night. Good stuff.
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Quoting Buhdog:
In case anyone missed it...a great shot of a rainbow and lightning from hollywood


DOUBLE RAINBOW!
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Here at 18N 63W... still waiting for the rain... Rain doesn't like those who need it or what!
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hi guys I really think that a low is forming at 16.5N 84.5W moving E-ENE
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Praying for some surf from 97l this weekend
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It looks like 97L is trying to flare up just a little and there appears to be some circulation there although disorganized. This could go up to 60-80% by later today, but that is just my prediction. Does anyone see any other signs of possible development with this AOI?
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Quoting afj3:
Question for all you experts out there: Why do they call it "recurve" as in "the storm will recurve out to sea?" Why not call it curve? The word recurve would suggest a second curving movement, as in repeat, restart, or reboot--i.e., doing the same thing again--a repeat of an earlier action. If a storm curves once, can it technically be recurving?


The simplest way to look at it is this: all tropical cyclones "want" to go poleward (north in the northern hemisphere). Once steering currents relax enough to allow a storm moving westward with the trade winds to finally follow its instincts, it'll make a turn (that is, a curve) to the right/north. However, once far enough north, the trade winds will cede control to the westerlies, which will generally alter the storm's natural northward movement and force it back toward the east or northeast...thereby giving it its second curve, or "recurve".

(A storm that starts out by moving north and then northeast, as often happens in the fall months, can't properly be said to recurve; it's merely turning eastward. By the same token, a storm that moves only westward then northward isn't recurving, either.)

There. Suitably confused? :-)
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Near miss is really a near hit
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Quoting afj3:
Question for all you experts out there: Why do they call it "recurve" as in "the storm will recurve out to sea?" Why not call it curve? The word recurve would suggest a second curving movement, as in repeat, restart, or reboot--i.e., doing the same thing again--a repeat of an earlier action. If a storm curves once, can it technically be recurving?


It's the same stupid thing like "near miss"
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12Z just updated

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Member Since: September 10, 2007 Posts: 0 Comments: 10577
Quoting NEwxguy:
My turn for the rain,shouldn't get as much as the rest of you along the coast,but going to be downpours and strong winds this afternoon here in eastern Mass.



Right now, it is sunny and very windy here on the south coast. The clouds are moving in very fast though.
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40. afj3
Quoting Waltanater:


It's a verb meaning to curve or bend back or backward. It is used properly but it is a good question.

I was doing research after I posted. I saw the definition of a recurve bow, which curves backwards....
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Quoting Jeff Masters:
The beginning of October traditionally marks the two-thirds point of hurricane season; approximately one-third of all named storms and hurricanes in the Atlantic season occur after October 1.

That may be the oral tradition or something, but storm histories suggest a completion factor closer to three-quarters or four fifths as of October 1:

% of season's storms forming by Oct 1:

All Tropical Storms: 1995-2009: 75%
1980-2009: 77%
1951-2000: 79%

Hurricanes: 1995-2009: 77%
1980-2009: 74%
1951-2000: 76%

Quoting Jeff Masters:
Tropical Storm Nicole brought us up to fourteen named storms for the year, so we should expect about four more named storms this year with one or two of these being hurricanes.

Looks like your projection acknowledges as much even if the text doesn't or else you'd probably be projecting an additional 7 or so storms to go with the 14 we've had.

One other point: there may be too few La Nina years on record to make this meanimngful, but La Nina years have generally had earlier peaks and smaller tails than other years. The CW of course is the opposite, but storm history does not support the idea of a La Nina season being expected to have a late peak or a long tail.
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Quoting afj3:
Question for all you experts out there: Why do they call it "recurve" as in "the storm will recurve out to sea?" Why not call it curve? The word recurve would suggest a second curving movement, as in repeat, restart, or reboot--i.e., doing the same thing again--a repeat of an earlier action. If a storm curves once, can it technically be recurving?


It's a verb meaning to curve or bend back or backward. It is used properly but it is a good question.
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Thanks for the update.
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34. afj3
Question for all you experts out there: Why do they call it "recurve" as in "the storm will recurve out to sea?" Why not call it curve? The word recurve would suggest a second curving movement, as in repeat, restart, or reboot--i.e., doing the same thing again--a repeat of an earlier action. If a storm curves once, can it technically be recurving?
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HPC discussion:
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
357 AM EDT FRI OCT 01 2010

VALID 12Z TUE OCT 05 2010 - 12Z FRI OCT 08 2010

THE GUIDANCE IS IN GOOD AGREEMENT THIS PERIOD IN DEVELOPING A
NEGATIVELY TILTED TROUGH FROM HUDSON BAY SOUTHEASTWARD THROUGH THE
NORTHEAST AND MAINTAINING A QUASI-STATIONARY DEEP CYCLONE
OVER/NEAR CALIFORNIA. THE 00Z GFS/00Z ECMWF ARE CLOSE TO THEIR
RESPECTIVE ENSEMBLE MEANS...SO CHOSE TO COMPROMISE BETWEEN THEM
FOR THE PRESSURES AND 500 HPA HEIGHTS FOR NEXT WEEK. THE 00Z
CANADIAN COULD NOT BE USED DUE TO ITS RECURVING HURRICANE-LIKE
VORTEX JUST OFFSHORE NEW ENGLAND INTO ATLANTIC CANADA MID TO LATE
NEXT WEEK. THE 16Z CONFERENCE CALL BETWEEN HPC AND NHC AGREED NOT
TO RECURVE THIS FEATURE...WHICH FITS THE 12Z MULTI-MODEL ENSEMBLE
GUIDANCE WHICH TRACKS IT SLOWLY THROUGH THE GREATER ANTILLES.

ROTH
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Quoting Buhdog:
In case anyone missed it...a great shot of a rainbow and lightning from hollywood


That's a great photo (from Mike Meadows)--but you forgot to point out the helicopter inside the rainbow. I lived in SoCal for a long time, and CG lightning in September, while not unheard of, is pretty rare. Excellent.

More images here
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My turn for the rain,shouldn't get as much as the rest of you along the coast,but going to be downpours and strong winds this afternoon here in eastern Mass.
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Just got off a Skype chat with a friend in the hills of Vermont a short ways north of Montpelier; she said the rain is coming down "in buckets", that the rain gauge on her porch, which read nothing this morning, now reads almost 4", and that the various gullies and ravines near her home are "loud with the sound of rushing water". All I could tell her was that it would be over with by this evening; she didn't seem comforted. :-)
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In case anyone missed it...a great shot of a rainbow and lightning from hollywood
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I really don't understand why a floater is not yet on invest 97L! I guess Floater 1 will go up live when it does as that is the one i have put on 97L
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Quoting Bordonaro:

Oh, La Nina is going to give you a fabulous rainy season this year, you will get to see heavy rains and snows, you may see a foot of rain in a storm or two and maybe a foot of snow on more than one occasion. It's payback from El Nino.


I don't mind a foot of snow.. a foot of rain.. no thank you...
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Quoting cat5hurricane:
Shear a little on the upswing near the area of 97L --> 12.5N 53.1W



Those coordinates are at least 24 hours old and are no longer valid. The low that they related to is the one I have referred to that is now near 13 N and 57 W where shear is low.
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Thanks, Dr. Masters. Amazing amount of rainfall from linear Nicole.
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From previous blog:

Quoting Neapolitan:
Good morning, Cotillion. Good points, yours. Please allow me to respond to them one by one:


Good morning.

To take each response:

- Yes, I will agree that Nicole is hardly the last. Even if October and November follows the form that recent inflated Septembers have produced, we should see Paula and Richard soon enough. I would be very surprised to see the season shut down at this point.

That said, Virginie and Walter?

Seeing 6 storms in October and November is a lot to ask. Only two seasons have ever managed 6 storms in October (1950 and 2005) and November isn't a month that can be relied on to produce anything (it's like June in that respect). It's not impossible, nor is it unfathomable, but it is unlikely.

As always, we will see.

- To tie the second and first part of the third together, yes there are a lot of people with that point of view. I understand the feelings and response of perplexity as well as understanding those who proclaim that 2010 underwhelmed the expectation. Depends on how you view hurricane season: some see it on a more broad level (i.e. scientifically) and of course, 14 storms with half of those becoming hurricanes by the end of September is exceptionally rare to see and is by no means a 'bust'.

On the other hand, especially after certain seasons of late, people wish to only explore how storms affect them directly (i.e. anthropocentric). Now, sure, there does lack a certain sense of an holistic approach in those types of comments (why the continual disregard to how countries such as Mexico have fared can be bamboozling), but it can at least be understood. Some do not care for the science behind it, they just want to know if they have to evacuate or not (of course, the argument about 'just look at the NHC!' is pertinent here. I say understanding, not necessarily anything beyond that).

Possibly because I only get hit by the remnants at best 99 times out of 100 (storms like Debbie and Faith aside), I find it difficult to really criticise that perspective.

And some are just trolls. Need not be expanded.

- As to the other point with storms missed, it has been raised a bit lately. Now, in doing so, it is not meant to disregard this season's activity nor to underplay its meaning. Without doubt, it is one of the most active seasons - at this point in time - that we have ever seen.

However, there is still that point to consider. The issue that two storms is actually one is valid to consider, but that is a minor point compared to missing the Gastons, the Nanas, the Jerrys of recent years. The trend of medium to long term storms has changed little even since 1900, let alone 1950. Some increase, yes, but not as much as it is made out to be at times. Would that be then countered by the Julias, the Lisas that were missed until a couple of decades ago?

There's no doubt that this is one of the more active seasons ever observed, even taking into account the lost Atlantic storms. It isn't a 1887/1933/2005 - however, it is looking likely to be comfortably bundled in with 1916, 1995 etc. The First Anomaly group and then the Second Anomaly group, perhaps.

It's more an issue of how active this period is in the long term. An average post-1995 of 14 named storms per year (2010 may end up upwardly adjusting that number) versus a theoretical re-adjusted climatological long term average of 13 named storms is not that impressive considering the coverage.

Again, this season is active - on its way to hyperactive in named storms and ACE - but how often are the active/hyperactive seasons, really?

That type of thinking is what I mean by not just looking at active vs bust.

Apologies to the tl;dr people...
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Its gonna be a beautiful weekend south of the mason dixon line!

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18. HCW
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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.

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