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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What, only 116 comments? Everybody must be enjoying the break....

Well, it's raining like crazy here.... must be the FROPA, since I'm not seeing any obviously tropical type developments via satellite....



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do all the models the high being strong?
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I know I am a newbie here, but I have been keeping statistics on if NHC forecast points verify with the radius of 2/3 probability they provide. I have the updated numbers through Nicole on my WU blog if anyone is interested.
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114. HCW
Quoting cat5hurricane:
Nice post. Thnx for the info.


No problem :) I'm surprised that more people don't know about IEM Bot. Our local NWS office warning feed has only 75 people following it. I have found that it works best when you use Tweetdeck or Trillian.
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Levi,

couple of quick questions for you. First, in your synopsis, you basically are saying that 97L should recurve. are troughs the only things that make storms recurve? Or are there other entities that make storms turn?

Second, are you thinking that either the High will not build back in time to force more of a westward push or you think the High will not be strong enough to prevent a recurve? thanks
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Great update Levi! Thanks!
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awesome update Levi! thank you!
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108. HCW
Are you tired of hitting F5 at advisory time waiting for for updates from the NHC ? If so I have found a way so that you don't have waste your energy reloading a page. It's IEM BOT on Twitter get Instant warnings, storm reports and NHC updates



http://twitter.com/iembot_HGX

This will work in your area also by changing the last 3 letters to your local radar code


If you have any questions feel free to shoot me a WU email . Have a great day James n Mobile
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106. Relix
97L looking awful
Member Since: August 3, 2006 Posts: 0 Comments: 2741
Quoting jasoniscoolman2011xz:
jason outside in the big wind storm
Wait until you see 150.
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This model shows something coming up out of the Caribbean into the Bahamas, and then gets pushed west towards Florida...Link
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Quoting weatherwart:


Thanks, Levi. Good update!
Quoting Bordonaro:

Great Update Levi, thank you!
Quoting DookiePBC:


Levi...excellent analysis as always!


Thank you, and you're welcome :)
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Quoting hydrus:
I see said this man with 4 eyes...:)...It almost looks like there could be a little ridging north of 97L...


Indeed, and there probably will be until 70W or so.
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Quoting Jeff9641:


Same as CMC and NOGAPS. CMC is just a little further N.


Ahh.... And this is 6+ days out, yes?
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Quoting Jeff9641:
FL may want to watch what could be OTTO next week as he looks like he may miss the turn North and head WNW.
Why do you think it will miss the turn to the north?
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Quoting Jeff9641:
Here comes OTTO on the 12Z GFS.


At 150 hours out?
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Quoting Levi32:
Just to clear it up, look at the 5-day movie of 850mb vorticity and anyone off the street can see plainly that Nicole ran up the eastern seaboard.

What I think Dr. Masters meant to say is that a piece of energy left behind by Nicole is bringing rain showers to the Caribbean. We all knew she was going to leave low pressure behind, but that does not mean she herself is still there in remnant form. She is gone. What is in the Caribbean now is a new entity.
I see said this man with 4 eyes...:)...It almost looks like there could be a little ridging north of 97L...
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Friday, October 1st, with Video


Levi...excellent analysis as always!
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Quoting Levi32:
Just to clear it up, look at the 5-day movie of 850mb vorticity and anyone off the street can see plainly that Nicole ran up the eastern seaboard.

What I think Dr. Masters meant to say is that a piece of energy left behind by Nicole is bringing rain showers to the Caribbean. We all knew she was going to leave low pressure behind, but that does not mean she herself is still there in remnant form. She is gone. What is in the Caribbean now is a new entity.

Great Update Levi, thank you!
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Friday, October 1st, with Video


Thanks, Levi. Good update!
Member Since: August 18, 2008 Posts: 0 Comments: 884
Just to clear it up, look at the 5-day movie of 850mb vorticity and anyone off the street can see plainly that Nicole ran up the eastern seaboard.

What I think Dr. Masters meant to say is that a piece of energy left behind by Nicole is bringing rain showers to the Caribbean. We all knew she was going to leave low pressure behind, but that does not mean she herself is still there in remnant form. She is gone. What is in the Caribbean now is a new entity.
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Quoting Levi32:



She did...
She sure left a lot of moisture in her wake though...
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Quoting EyeWallPaperInc:
From a climatology perspective is there an explanation for the mid August and mid October peaks on each side of the main peak of the hurricane season. One would think with a 100 years of records we would see more of an even bell curve.


And there's the catch. We don't actually have 100 years of records. Well, not accurate records anyway. Until the satellite age, a lot of activity could, and almost certainly did go unnoticed.

Another thing to keep in mind when it comes to statistics. They're only as complete as the data that was used to derive them. So if every year was counted, you have a better chance at valid statistics. But if they 'throw out' years for whatever reason, the statistic is useless.

Statistics can manipulated to prove whatever you want.
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Quoting hydrus:
(From Dr.M,s blog>...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. ............................,(I thought Nicole moved north into the Carolina,s..
I may be mistaken, but I think they dropped Nicole somewhere north of Cuba, and what was Nicole was split with part being pulled both north into the low sitting of the South Carolina coast, and the rest south to the Caribbean.

MODIFIED: I concede to Levi, post #79
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From a climatology perspective is there an explanation for the mid August and mid October peaks on each side of the main peak of the hurricane season. One would think with a 100 years of records we would see more of an even bell curve.
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Good Afternoon, any observations about 97 ?
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Quoting hydrus:
(From Dr.M,s blog>...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. ............................,(I thought Nicole moved north into the Carolina,s..



She did...
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This is a blog for the true weather lover. I am around winter, spring, summer and fall.

Those who drift away are losing out on good conversation about weather and they're missing out on learning about changing upper air patterns, winter storms and severe weather forecasting :O).
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The blog has slowed along with the hurricane season. I'm out till June 1st of the 2011 hurricane seaason which should be a very active conus hitting season lol. Don't listen to the experts as for the don't have a clue on what the hell they are talking about. Peace out WU bloggers, its been a treat. I'm letting my gaurd down as of now...
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Storm distribution over time.

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What is with this cloud deck in FT myers today? Thought it was supposed to be dry and sunny.
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(From Dr.M,s blog>...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. ............................,(I thought Nicole moved north into the Carolina,s..
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Quoting kmanislander:


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.
Goodmorning, Ive seen coordinates with 97L all over the place. This morning tropical atlantic has it at 15.7 N 49.7 W
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Good morning all.

Tropical Tidbit for Friday, October 1st, with Video
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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? :-)


Your so Smart
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Quoting CaptnDan142:


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.


"approximately one-third of all named storms and hurricanes in the Atlantic season occur after October 1"

not referring to time. referring to named storms.
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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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