An active Atlantic hurricane period coming

By: Dr. Jeff Masters , 1:48 PM GMT on August 17, 2010

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The remnants of Tropical Depression Five are no longer a threat, done in by high wind shear and close proximity to land. However, an active period for Atlantic hurricanes is likely for the remainder of August, as the global atmosphere undergoes a major change to the circulation pattern that has dominated Northern Hemisphere weather during July and August. A large trough of low pressure is gathering strength over Europe, and is expected to push eastward. By Thursday, this trough should be able to push away the blocking ridge of high pressure that has given Russia its worst heat wave in history. The shift in circulation has already weakened the large region of sinking air that has brought dry, stable conditions to the tropical Atlantic over the past month. Vertical instability, which was unusually low since late July, has now returned to near normal levels over the tropical Atlantic (Figure 1), though it remains quite low over the rest of the North Atlantic. Instability is measured as the difference in temperature between the surface and the top of the troposphere (the highest altitude that thunderstorm tops can penetrate to.) If the surface is very warm and the top of the troposphere is cold, an unstable atmosphere results, which helps to enhance thunderstorm updrafts and promotes hurricane development. Since SSTs in the Atlantic were at record highs and upper tropospheric temperatures were several degrees cooler than average in July, enhancing instability, something else must have been going on to reduce instability. Dry air can act to reduce instability, and it appears that an unusually dry atmosphere, due to large-scale sinking over the Atlantic, was responsible for the lack of instability. Now that vertical instability has returned to near normal levels, Atlantic hurricane activity should increase to at least average levels over the next two weeks. This is particularly true since SSTs are at record highs and vertical wind shear is at average to below average levels over the tropical Atlantic.


Figure 1. Vertical instability (in °C) over the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right) in 2010. Normal instability is the black line, and this year's instability levels are in blue. The atmosphere became much more stable than normal in both regions at the end of July. This lack of instability also extended to the Gulf of Mexico and North Atlantic Ocean between Europe and North America. However, in the past few days, vertical instability has returned to normal, thanks to a major pattern shift in the global atmosphere. Image credit: NOAA/CIRA.


Figure 2. The climatology of Atlantic hurricane activity shows a sharp rise in activity around August 18.

Analysis
August 18 historically marks the point where Atlantic hurricane activity makes a major spike upwards (Figure 2.) On average, we can expect to see two named storms and one hurricane during the last half of August. The last half of August usually sees a moistening of the atmosphere off the coast of Africa, as the the African monsoon kicks into high gear. This year is no exception (Figure 3.) The dry Saharan Air Layer (SAL) has retreated to the north, leaving a moist atmosphere conducive for tropical cyclone development off the coast of Africa.

It would not be a surprise to see atmospheric instability increase to above-average levels by early next week as the major atmospheric pattern shift progresses. Will this usher in a hyperactive period of Atlantic hurricane activity next week, with a parade of three or four simultaneous storms strung out across the Atlantic? Probably not, since the Madden-Julian Oscillation (MJO) only marginally favors upward motion over the tropical Atlantic, and is not forecast to change much over the next ten days. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The bottom line: I expect we will see 2 - 3 named storms in the Atlantic by the end of August, including one hurricane. Where these storms might develop and move is difficult to say. It currently appears that the global shift in circulation will bring near-average steering currents to the Atlantic over the next ten days, with a series of troughs of low pressure capable of recurving hurricanes, moving across the Atlantic. The GFS model is indicating, though, that during the few days of August, these troughs may weaken, making recurvature of hurricanes less likely, and increasing the probability of landfalling storms.

The GFS, NOGAPS, and ECMWF currently predict that one or two tropical storms will form between Africa and the Lesser Antilles Islands during the period 4 - 10 days from now. The NOGAPS model is predicting the development of a strong tropical disturbance near the coast of Honduras late this week.


Figure 3. Saharan Air Layer (SAL) analysis shows that the dry air and dust of the SAL (orange colors) lies well to the north of the hurricane breeding grounds off the coast of Africa, near the Cape Verdes Islands. Image credit: University of Wisconsin/NOAA Hurricane Research Division.

Smoke bedeviling Moscow again
Light easterly winds over the past few hours have brought smoke from wildfires back into Moscow today. Temperatures at Moscow's Domodedovo airport hit 29°C (84°F) today, which is 11°C (20°F) above average. The latest forecast for Moscow predicts that just one more day remains for Russia's greatest heat wave in recorded history. On Thursday, a strong trough of low pressure will move through European Russia, finally bringing below average temperatures.

Jeff Masters

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1149. xcool


108hrs
Member Since: September 26, 2009 Posts: 2 Comments: 15624
Ever wondered why hail is not commonly seen with Tropical Systems? Read my recent blog and learn the answer!

Link
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GFS is still developing PGI31L rather than its brother further to the north (30L).

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1146. will45
Quoting hydrus:
It resembles that path too. Hugo was very bad.


Yes i heard that you can still see the affects in the forrest areas of SC
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1145. SQUAWK
Quoting CoopsWife:


Yep, I''m pretty familiar with that year. It was a very bad year here in the Tidewater.


You were there in '33?????? Cut it out - say it ain't so!
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Dag nabbit, I was wishcasting for a nice QUIET season !!!
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PGI27L getting ready for nightfall. What'll happen overnight? We'll see. (Click the image for a large version.)

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Quoting hydrus:
Well, some of the Mets did use 33 as an analog year. Another thing that is worth noting, the Chesapeake Bay area sticks out there pretty far. Yall have had your share of storms and will have many more i,m afraid....Check this out, the full list of 1933 storms. 21 in all...Link... Be sure to scan downward for individual tracks.


Yep, I''m pretty familiar with that year. It was a very bad year here in the Tidewater.
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Quoting Drakoen:


Yea, I looked up the monthly mean temperatures to know what to pack for the Fall.


Actually Drak probably has a complete Weather Synopsis for the Tally region!
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1139. hydrus
Quoting will45:


more like a hugo hit
It resembles that path too. Hugo was very bad.
Member Since: September 27, 2007 Posts: 1 Comments: 20518
1137. xcool


90hr
Member Since: September 26, 2009 Posts: 2 Comments: 15624
18z GFS trending stronger than the 12z run. In the 12z run it was still a weak TD (1010mb) by 72 hours, now by 72 hours it's a weak TS (1005mb).
Member Since: September 2, 2009 Posts: 130 Comments: 21091
if it develop tomorrow or so it will be like 1986, 1998 and 2004 Danielle history maker but perhaps further west.
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I see a yellow hatch so It looks like things are picking up.....be back to discuss if there is a TD. Have a great afternoon folks.....
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72 hours:

Member Since: September 2, 2009 Posts: 130 Comments: 21091
1131. KEEPEROFTHEGATE (Mod)
AOI/XX/XX
MARK
15.25N/67.45W

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Quoting Drakoen:


Classes start next Monday


Drak starts school, then he will be too stuck up to hang out with us anymore! LOL

Drak, promise you want get stuck up1 :D
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This track is scary if it is correct.
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1128. will45
Quoting MiamiHurricanes09:
No way, much further south. It appears to me that the track that he set is at the bottom of the flag pole.


more like a hugo hit
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Starting to think again this might be our system. Or at least what triggers PGI31L to develop..
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1126. xcool


66hrs
Member Since: September 26, 2009 Posts: 2 Comments: 15624
Quoting btwntx08:
can anyone see my posts excluding squwak

Hi there!
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1124. xcool
ha
Member Since: September 26, 2009 Posts: 2 Comments: 15624
Quoting tkeith:
I cant see your posts...you've got me poofed.

unpoof me then I'll be able to see them.
LMAO!
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting tkeith:
yes he was and me too...can you hear me?
Hey, BTWN. Somebody said u'd been minused or banned or something, but I was pretty sure I saw u a minute before that, being all innocuous and all... couldn't figure out why that would happen.
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1121. tkeith
Quoting btwntx08:
can anyone see my posts excluding squwak
I cant see your posts...you've got me poofed.

unpoof me then I'll be able to see them.
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1120. SQUAWK
Quoting hydrus:
Well at least you did not forget your sense of humor. Dont ever lose that, you will live a longer and happier life. I am not just saying that, its the truth...:)

I am 100% onboard with that. Just 'cause I like to stir the pot every once in a while, doesn't mean I am not having fun. Even with our friend. Funny how he usually cuts and runs when I show up. I like that. He earned it.
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54 hours:

Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting MiamiHurricanes09:
Oh, my bad.

I would assume that he means the bottom, it could also be the entire pole. LOL, funny that we're looking into flagpoles. Either way, we'll find out soon enough.
See, that's the problem with "cutesy" graphics. Too open to misinterpretation by the weather blogging public....

I suppose by tomorrow we'll all have a better handle on formation of both ECar and EAtl Twaves...

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1116. hydrus
Quoting CoopsWife:


Noooooooo. Don't say that. ROFL!!!

According to the old storm info, I'll be underwater, and I'm 21 feet plus above sea level and 11 miles from the oceanfront! Of course, I'm only 2 -3 miles south of the Bay, but still.....
Well, some of the Mets did use 33 as an analog year. Another thing that is worth noting, the Chesapeake Bay area sticks out there pretty far. Yall have had your share of storms and will have many more i,m afraid....Check this out, the full list of 1933 storms. 21 in all...Link... Be sure to scan downward for individual tracks.
Member Since: September 27, 2007 Posts: 1 Comments: 20518
1115. tkeith
Quoting btwntx08:
bahahurrican lookin for me??
yes he was and me too...can you hear me?
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1114. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15624
It will emerge tomorrow afternoon

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Quoting BahaHurican:
He said "for tropical development". Gotta take the whole phrase. So something is certainly going to develop, but how much and where it'll go isn't certain.

I still have a problem with that flagpole base. Unless he means anywhere from S FL to the Carolinas? [sorry Press]
Oh, my bad.

I would assume that he means the bottom, it could also be the entire pole. LOL, funny that we're looking into flagpoles. Either way, we'll find out soon enough.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
1110. xcool


42hr
Member Since: September 26, 2009 Posts: 2 Comments: 15624
1109. tkeith
Thank you for your patience. You may now return to discussing 368-hour model runs, pouch tracking, invests, and JFV's current emotional state. ;-)

and NFL football...
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1108. hydrus
Quoting SQUAWK:


Knew I forgot something! Thanks! LOL
Well at least you did not forget your sense of humor. Dont ever lose that, you will live a longer and happier life. I am not just saying that, its the truth...:)
Member Since: September 27, 2007 Posts: 1 Comments: 20518
Strong Tropical Wave

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Quoting MiamiHurricanes09:
Look at the image, it has it on south/central Florida's doorstep. He also said the future looks certain, he then said the path and intensity looks iffy. Oh well, nothing to look into, just what I understood.
He said "for tropical development". Gotta take the whole phrase. So something is certainly going to develop, but how much and where it'll go isn't certain.

I still have a problem with that flagpole base. Unless he means anywhere from S FL to the Carolinas? [sorry Press]
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1103. xcool


i'm model cast here hahaha
Member Since: September 26, 2009 Posts: 2 Comments: 15624
1102. SQUAWK
Quoting hydrus:
Squawk....Did you have your Geritol today?...You seem grouchy.:)


Knew I forgot something! Thanks! LOL
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1101. xcool


24hr
Member Since: September 26, 2009 Posts: 2 Comments: 15624
Quoting MiamiHurricanes09:
No way, much further south. It appears to me that the track that he set is at the bottom of the flag pole.
Ah, he treks that flagpole bottom right across the Bahamas, too!

This based on one run from one model? Wow.
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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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