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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1600. angiest
Quoting FloridaToz:
It is going to explode tomorrow....(nothing happens).... It is going to blow up by the weekend....(a weak prayer of a depression dies)

Predictions, models, graphs, etc. I hope we get something for the board to talk about soon, the wish-casting is getting fatiguing



I dont think everyone is wishcasting. I think this year is teaching us we still have a lot to learn about the conditions necessary for tropical cyclogenesis.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting troy1993:
Does the wave that is about to emerge off Africa have any sort of circulation with it?
Vigorous mid-level circulation. If you look at satellite loops you'll see the cyclonic curvature.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1597. angiest
Quoting GBguy88:


Weird though it may be to call it based on a name only, I'd have to agree. And I think Fiona could be interesting. They just sound like historically significant names. Now if we can nail down a track with our premonitions, we'll be doing alright :P


Fiona will be a bad one. A real ogre.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1596. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting NHCstevehayward:

yes indeed!! if you'll notice that they appear to be below the latitude of the cape Verde islands, that gives these waves a less chance of re curving out to sea
Very true. They're picking a pretty good latitude to emerge at.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Accuweather thinks we'll see some development from the wave in the carribean.
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Does the wave that is about to emerge off Africa have any sort of circulation with it?
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Good evening.

What are the GFS showing on storm they develop?
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Quoting JavPR:
that wave southwest of PR is hitting hard the southwest area of Cabo Rojo and Mayaguez PR...I just got heavy winds in the northwest of the island...

thanks for the update looks to be a vigorous wave regardless of development!
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Quoting BahaHurican:
Somebody pls remind me when 00Z model runs are supposed to be available?

Ta.
GFS starts at around 11:30p.m EDT, finishes around 1:15a.m EDT. CMC about the same time that the GFS finishes. NOGAPS updates around the same time as the CMC. UKMET around 2a.m EDT. ECMWF around 3:15a.m EDT.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1588. JRRP
Quoting BahaHurican:
Somebody pls remind me when 00Z model runs are supposed to be available?

Ta.

11:30 pm
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from the san juan office

.DISCUSSION...IN THE LATER TERM THE APPROACH OF A TUTT LOW WILL
PRODUCE FAVORABLE CONDITION OVER THE AREA AND HAVE ADJUSTED POPS
THURSDAY THROUGH FRIDAY MORNING. THE NEXT TROPICAL WAVE MAY BE
CONNECTED TO AN APPROACHING TROPICAL SYSTEM AND IS ALSO EXPECTED
TO BRING INCREASED SHOWER ACTIVITY ON MONDAY AND TUESDAY.

IT IS STILL TOO EARLY TO SAY MUCH ABOUT THE SYSTEM EXPECTED IN BOTH
THE GFS AND ECMWF THAT PASSES NORTHEAST OF THE AREA...POSSIBLY ON
THURSDAY OF NEXT WEEK...BY VERY LITTLE OR A CONSIDERABLE
DISTANCE...DEPENDING ON MODEL RUN TIME AND TYPE...BUT MODELS HAVE
BEEN ADVERTISING DEVELOPMENT FOR OVER 48 HOURS WITH ROUGHLY
SIMILAR TRACKS AND TIMING.

Member Since: Posts: Comments:
It is going to explode tomorrow....(nothing happens).... It is going to blow up by the weekend....(a weak prayer of a depression dies)

Predictions, models, graphs, etc. I hope we get something for the board to talk about soon, the wish-casting is getting fatiguing

Member Since: Posts: Comments:
1585. GBguy88
Quoting washingtonian115:
I think Igor will be the big bad boy of the season.It has that look...The name that is.


Weird though it may be to call it based on a name only, I'd have to agree. And I think Fiona could be interesting. They just sound like historically significant names. Now if we can nail down a track with our premonitions, we'll be doing alright :P
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Quoting jasoniscoolman2010x:
big ridge over SE Canada argues very bad news for the usa.
You just said we would see fish storms....
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Hey, zoomiami. Any boomers today?
Member Since: October 25, 2005 Posts: 19 Comments: 22583
This is a great satellite image of Africa (that updates every 15 minutes!). If you look at the loop, you'll notice just how fast these tropical waves are moving. Likely that the first one will emerge tomorrow evening with the one east of it the next day.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
1580. JavPR
that wave southwest of PR is hitting hard the southwest area of Cabo Rojo and Mayaguez PR...I just got heavy winds in the northwest of the island...
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Somebody pls remind me when 00Z model runs are supposed to be available?

Ta.
Member Since: October 25, 2005 Posts: 19 Comments: 22583
Quoting KanKunKid:


Yeah, they call that location...my back yard!

I'm A Caymanian, live here , love here , wouldn't trade it for anywhere else in the world, but we often refer to it as the ROCK, and really all it is is a piece of land in the vast ocean'but a great piece of land" I sure didn't take offence to your comment as you basically spoke the truth most storms that affect usually head your way so you pay close attention to what happens in our neck of the woods, I'm not too sure what happened to 'wunderkidcayman' that he took offense to your comment or he made a poor try at a sense of humor, one never knows, just forgive him as I'm sure he realised his comment was not appropriate.
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1576. xcool


PGI27L
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting StormSurgeon:


...and tattled on to boot!


lol
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I think Igor will be the big bad boy of the season.It has that look...The name that is.
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Quoting blsealevel:


Thanks storm i was looking for that


Also, contact your local NWS. They usually do one or two training sessions per year. We hosted one at our station last month.
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1570. xcool


Member Since: September 26, 2009 Posts: 2 Comments: 15684
Well, that was quick. Pre-TWO.... everything is cool.... post TWO? Nuthouse....

As Pat likes to remind pple, have a Fresca .......[or, I extend any potable beverage designed to soothe rather than invigorate].
Member Since: October 25, 2005 Posts: 19 Comments: 22583
1567. JRRP

Link
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Quoting StormW:
For anyone interested:

SKYWARN


Thanks storm i was looking for that
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hey guys, good evening!

Is anyone else having the feeling that the Atlantic Basin is like a microwave heating up steadily the popcorn (tropical systems) until we hear the first pop followed by a giant wave of pops roaring on the microwave?

When do you think the first important pop will be heard?

A. Within 1 week
B. Last week of August
C. September
D. Cheap useless popcorn that didn't worked at all.
E. Get a new microwave.
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Have a good evening guys. Have fun figuring it all out. :)
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Quoting pilotguy1:


And of course you are one of the sane people?


LMAO!!!
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1562. robj144
Quoting YourCommonSense:


So did the QBO affect HANNAH


I thought you were talking about astrophysical gravity waves. This would be huge news if this actually happened from an astrophysical source!
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1560. Levi32
Quoting YourCommonSense:


So did the QBO affect HANNAH


Not sure what the author of that video meant by "gravity wave"....it was an upper trough at work plus entanglement with Hispaniola that killed Hannah. The QBO is also not something you can really tie to specific storms....it's more of a large-scale factor affecting seasonal activity as a whole, like the MJO.
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Quoting Abacosurf:


Wait till the carribean wave and the storm by Nica meet up north of Honduras.....

Nogaps has been pointing to something for a few days now.
You mean for 3 months now?.
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Quoting washingtonian115:
More gloom,and doom grahpics.lol.
LOL, I can post plenty.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting MiamiHurricanes09:
Anticyclone over the tropical wave nearing the African coast. You can tell that the anticyclone is really helping the system out because of the good outflow channels the tropical wave has.

More gloom,and doom grahpics.lol.
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1556. JRRP
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1555. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15684
Quoting stormpetrol:
I think the area off Nicaragua bears watching, sames to be moving offshore. Sorry if this is the 2nd post, my post seems to be eaten up this evening!


Wait till the carribean wave and the storm by Nica meet up north of Honduras.....

Nogaps has been pointing to something for a few days now.
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Quoting sammywammybamy:
Well the Blog is Still Full of Crazy and Annyoing People.....

Wheres DestinJeff and IKE? Two of the Sane People in here...

Its a Mad-House..
There's more sane people on the blog than you think.
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I'm on vacation! Birthday Week so going to be good.
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Quoting hydrus:
Yeah. I noticed that one this morning.
It has been very persistent throughout the day. I think it is a surface trough if I am understanding the surface map.
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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.