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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2650. jonelu
10:37 PM GMT on August 18, 2010
Quoting utilaeastwind:
Any thoughts on the circulation developing SSE of Jamaica?



Looks unlikey...NHC says 10%
Member Since: October 31, 2007 Posts: 2 Comments: 882
2649. utilaeastwind
2:19 PM GMT on August 18, 2010
Any thoughts on the circulation developing SSE of Jamaica?

Member Since: October 12, 2007 Posts: 0 Comments: 192
2648. IKE
2:15 PM GMT on August 18, 2010
NEW BLOG!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2647. IKE
2:12 PM GMT on August 18, 2010
If I had had a daughter I always thought Danielle was a pretty name. Closest song I could find...yeah...he's singing about a male...who cares....I think it's pronounced the same:)

Member Since: June 9, 2005 Posts: 23 Comments: 37858
2646. homelesswanderer
2:09 PM GMT on August 18, 2010
I think everyone should just keep up with what's going on out there. If these storms do start spinning up, especially on the other side of the Atlantic, they could go ANYWHERE. I follow the models too. And like to watch the storms and talk about where they might go. But I've had a few recent experiences with storms in strength and track that the models either didn't pick up on or did so at the last second. Humberto the obvious blown "strength" forecast. And as the Hubs and I were talking about yesterday the forecast track of Ike went down to the morning of the 11th (he hit at 2am the 13th), when our local officials came on the TV and said, "The buses are in South Texas but Leave now." What they meant was that the state resources were still farther down the coast where they had been sent because that's where everyone said Ike would go. I live on the up Tx coast, La border. Water was already covering some of the roads here even that early. They made a gutsy and correct call that morning. So if there's a storm in the Atlantic basin watch it well until you're sure it's not coming your way. I wish models could tell us 2 weeks in advance where these things will go. Ah well, maybe someday. :)
Member Since: August 15, 2008 Posts: 10 Comments: 3665
2645. CybrTeddy
2:07 PM GMT on August 18, 2010
Quoting YourCommonSense:
Dry Hair destroying every little ball of convection in its path.


Best wash it.
Member Since: July 8, 2005 Posts: 259 Comments: 23015
2643. hurricanejunky
2:03 PM GMT on August 18, 2010
GFS, NOGAPS and ECMWF all seem to develop a CV storm (intensity varies based on model) by the Monday/Tuesday range near northern leeward islands. CV season finally in gear?
Member Since: August 28, 2006 Posts: 6 Comments: 2895
2642. alaina1085
1:59 PM GMT on August 18, 2010
Quoting Jeff9641:


Enjoy it as your rain may come to a end for quite sometime starting in about 2 to 3 days. Northern LA is been all over the news recently because of a terrible drought of extreme porportions.

Im a little farther south east of that, so no rain here. Im sure we will have some more today tho. But yea im actually enjoying it because the temps are cooled off... but the humidity is still a KILLER!
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2641. StormChaser81
1:58 PM GMT on August 18, 2010
GFS 7 days from now. Wow thats an impressive system.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
2639. alaina1085
1:56 PM GMT on August 18, 2010
Quoting LAlurker:
Looks like xTD5 has finally gotten it's act together. Plenty of convection all around CoC now.

It likes land better then water!
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2638. ShenValleyFlyFish
1:55 PM GMT on August 18, 2010
Quoting LAlurker:
Looks like xTD5 has finally gotten it's act together. Plenty of convection all around CoC now.
Anybody know where to find a track projection for x05L?
Member Since: September 9, 2007 Posts: 36 Comments: 4687
2636. alaina1085
1:54 PM GMT on August 18, 2010
Link

Baton rouge, LA... is getting hammered. Thanks ex TD 5....
Member Since: August 2, 2006 Posts: 0 Comments: 1240
2635. nrtiwlnvragn
1:53 PM GMT on August 18, 2010
Some cyclonic curvature on latest ASCAT


Member Since: September 23, 2005 Posts: 13 Comments: 10471
2633. LAlurker
1:51 PM GMT on August 18, 2010
Looks like xTD5 has finally gotten it's act together. Plenty of convection all around CoC now.
2632. MahFL
1:51 PM GMT on August 18, 2010
What does + NAO mean for recurving ?
Member Since: June 9, 2004 Posts: 0 Comments: 2912
2631. itrackstorms
1:50 PM GMT on August 18, 2010
Quoting NJ2S:
i totally agree that its way to early to rely on models.....anywhere from nicaragua to canada is a potential target at this point....BUT its good to watch b/c if they dont change 5-6 days from now and a place like NYC is threatened they will require way more warning time then the more prepared SE & gulf.


That might be a stretch... just a bit.
Member Since: July 20, 2008 Posts: 0 Comments: 152
2629. reedzone
1:50 PM GMT on August 18, 2010
With the NAO going positive, I'm not so sure the system will recurve, NAO going positive means more ridging. The GFS has been showing this, more CONUS impacts. It's just something to really speculate right now.
Member Since: July 1, 2008 Posts: 13 Comments: 7334
2628. AstroHurricane001
1:47 PM GMT on August 18, 2010
The second storm shown on the long-range GFS (future Fiona?) looks like it takes a track very similar to Georges, and could be a cat. 2 crossing Haiti.
Member Since: August 30, 2008 Posts: 8 Comments: 2834
2626. TheCname
1:44 PM GMT on August 18, 2010
It looks like an Isabel track almost.
Member Since: April 15, 2010 Posts: 0 Comments: 22
2625. pottery
1:44 PM GMT on August 18, 2010
Quoting Snowlover123:
0Z GFS, and I know this is subject to change, shows a major hurricane hitting my area. It also develops storm 2, but takes it into the Carribean...



Direct impact.



Storm #2 entering the Carribean...

-Snow

Those models that bring storms into the Caribbean are all WRONG.
(he says with Downcast Flag Waving....)
Member Since: October 24, 2005 Posts: 0 Comments: 23105
2624. NJ2S
1:44 PM GMT on August 18, 2010
i totally agree that its way to early to rely on models.....anywhere from nicaragua to canada is a potential target at this point....BUT its good to watch b/c if they dont change 5-6 days from now and a place like NYC is threatened they will require way more warning time then the more prepared SE & gulf.
Member Since: August 2, 2010 Posts: 0 Comments: 115
2623. IKE
1:41 PM GMT on August 18, 2010
Quoting YourCommonSense:


Models are disregarding the -NAO. Correct?


Goes positive by the 28th on the latest ECMWF...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
2622. RipplinH2O
1:39 PM GMT on August 18, 2010
Howdy all...
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2621. MahFL
1:39 PM GMT on August 18, 2010
The wave about to exit Africa is massive.....
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2620. StormSurgeon
1:39 PM GMT on August 18, 2010
Quoting Snowlover123:


The question is though, where IS the axis of the trough? And model forecasting 10 days out is usually not trusted...


A model beyond three days shouldn't be trusted.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
2618. IKE
1:38 PM GMT on August 18, 2010
Morehead City,NC....

LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 2 PM TUE...DRY FRI AFTN INTO SAT AS HIGH PRES BUILDS INTO
THE REGION AND SLOWLY SLIDES OFFSHORE. BOTH GFS/ECMWF SHOW SHARP
UPR TRF/POSS UPR LOW DEVELOPING OVER THE AREA EARLY NEXT WEEK.
THIS FEATURE WILL LEAD TO AT LEAST WIDELY SCT CONVECTION WITH A
SFC FRONT EXPECTED TO BE IN THE VICINITY. HIGHS FRI AND SAT WILL
CONTINUE IN THE LOWER 90S INLAND...FALLING HGTS WILL KEEP HIGH
TEMPS MAINLY IN THE 80S EARLY NEXT WEEK.


Long term Wakefield,VA...

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
ZONAL MID LVL FLOW WILL CONTINUE INTO PORTIONS OF THE WKND OVR THE
ERN CONUS. ENHANCED WV IMGRY FINALLY SHOWING A TROF DEEPENING OFF
THE COAST OF ALASKA AND THIS WILL EVENTUALLY PUSH S/SE INTO THE PAC
NW RGN (WHICH MODELS HAVE SIGNALED AT, BUT HAVE BEEN TOO EAGER TO
BRING IT IN TOO SOON). SHRTWV CRNTLY MOVING OVER THE PAC NW WILL
MOVE INTO THE CENTRAL CONUS OVER THE NEXT FEW DAYS ALONG THE NRN
EXTENT OF A MID LVL RIDGE THAT WILL EVENTUALLY BUILD NORTHWARD AS
THE AFOREMENTIONED TROF DEEPENS OVER THE PAC NW. THIS SHRTWV MAY
EVENTUALLY GET INFUSED INTO A TROF THAT BREAKS OFF FROM THE CUT OFF
SYSTEM CRNTLY CHURNING OVER THE HUDSON BAY RGN AND PUSH S/SE ON THE
FRONTSIDE OF THE DVLPG RIDGE AXIS INTO THE ERN CONUS. THIS IN TURN
COULD LEAD INTO A CUT OFF SYSTEM DVLPG OVER THE MID ATLC RGN
EARLY NEXT WK.

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2617. stoormfury
1:38 PM GMT on August 18, 2010
area of disturbed weather near 8N 38W with a mid level circulation
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2616. largeeyes
1:36 PM GMT on August 18, 2010
If the bread you buy in reaction to a model predicting a cane would be moldy by the time it got to you, you probably shouldn't trust it.
Member Since: August 22, 2006 Posts: 0 Comments: 1449
2614. hurricane23
1:34 PM GMT on August 18, 2010
Quoting Snowlover123:


The question is though, where IS the axis of the trough? And model forecasting 10 days out is usually not trusted...


No kidding? Just pure speculation at this point. A look at the larger scale pattern changes on the ensemble mean show any tc that gains sufficient latitude could recurve.
Member Since: May 14, 2006 Posts: 8 Comments: 13597
2613. MahFL
1:31 PM GMT on August 18, 2010
Quoting SaintPatrick:


Thanks for posting the Louisiana radar throughout the day Pat. Im at work and can't ever look at it because they have alot of websites blocked! ;[


Lol that one is not blocked then as you can see it......
Member Since: June 9, 2004 Posts: 0 Comments: 2912
2612. angiest
1:31 PM GMT on August 18, 2010
Quoting Snowlover123:
0Z GFS, and I know this is subject to change, shows a major hurricane hitting my area. It also develops storm 2, but takes it into the Carribean...



Direct impact.



Storm #2 entering the Carribean...

-Snow


Almost looks similar to a David/Frederick setup.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
2611. Snowlover123
1:29 PM GMT on August 18, 2010
Quoting hurricane23:


Ensembles and OP models all seem to agree on some form of an east Coast trough around 7-10.


The question is though, where IS the axis of the trough? And model forecasting 10 days out is usually not trusted...
Member Since: April 1, 2010 Posts: 9 Comments: 2699
2610. StormSurgeon
1:29 PM GMT on August 18, 2010
Quoting CrazyDuke:


It's one of those things I'd rather be wrong about. I just hope helps keep this board healthier than it would be otherwise.


Agreed.......and you're not wrong.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
2609. hurricane23
1:28 PM GMT on August 18, 2010
Quoting jasoniscoolman2010x:
last night 80% fish storm now is 50% of being a fish storm.


Ensembles and OP models all seem to agree on some form of an east Coast trough around 7-10.
Member Since: May 14, 2006 Posts: 8 Comments: 13597
2608. Snowlover123
1:28 PM GMT on August 18, 2010
0Z GFS, and I know this is subject to change, shows a major hurricane hitting my area. It also develops storm 2, but takes it into the Carribean...



Direct impact.



Storm #2 entering the Carribean...

-Snow
Member Since: April 1, 2010 Posts: 9 Comments: 2699
2607. PensacolaDoug
1:27 PM GMT on August 18, 2010
Quoting LavosPhoenix:


Let me guess, they turned it into yet another Waffle House...



WH rules!
Member Since: July 25, 2006 Posts: 0 Comments: 519
2606. NJ2S
1:26 PM GMT on August 18, 2010
http://raleighwx.easternuswx.com/models/gfs/00zgfs500mbHGHTPMSLtropicalGFSLoop.html
Member Since: August 2, 2010 Posts: 0 Comments: 115
2605. IKE
1:25 PM GMT on August 18, 2010


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2604. PensacolaDoug
1:25 PM GMT on August 18, 2010
G'morn back at ya CT.
Member Since: July 25, 2006 Posts: 0 Comments: 519
2603. CrazyDuke
1:24 PM GMT on August 18, 2010
Quoting StormSurgeon:
...that was quite a sermon.


It's one of those things I'd rather be wrong about. I just hope helps keep this board healthier than it would be otherwise.
Member Since: February 13, 2007 Posts: 0 Comments: 140
2601. TampaSpin
1:20 PM GMT on August 18, 2010
The GFSX long range are showing fish storms after a scrape with the Northern Caribbean Islands and a near Puerto Rico and a near Bermuda scrape.
Member Since: September 2, 2007 Posts: 177 Comments: 20430
2600. breald
1:20 PM GMT on August 18, 2010
Quoting NJ2S:


so we are possibly(although the models cam/will change way too far out ) BUT POSSIBLY looking at a Gloria or Bob impact??


I remember both those storm very well. Come to think of it, I have lived in three different states along the east coast and have experienced at least one hurricane in each state. NC, Hurricane Fran, Florida 2004 and Mass the two storms above storms. I think it is time for me to move into one of those square states in the middle of the country. But then again, they have their own weather issues.
Member Since: May 28, 2008 Posts: 38 Comments: 5303

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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.