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La Niña is gone

By: Dr. Jeff Masters , 03:13 PM GMT del 11 Maggio 2006

The La Niña of 2006 proved to be short-lived. Sea Surface Temperatures (SSTs) in the eastern Pacific near the Equator have returned to near-normal values over the past month, according to the latest El Niño advisory issued today by the Climate Prediction Center (CPC). We are now in what is characterized as ENSO-neutral conditions (or El Niño-neutral conditions), which means that there is neither an El Niño nor a La Niña occurring. This is the case about 45% of the time, and was true for March through December of 2005. The CPC expects El Niño-neutral conditions to continue for at least the next 3-6 months, which means for all of hurricane season. The 2006 La Niña was an unusual one, because it started very late--no La Niña of similar magnitude has ever formed in the middle of winter, as this one did. However, the demise of this year's La Niña came at the usual time such events end--April and May are the typical months for the demise of both La Niña and El Niño.

How will this affect the hurricane season of 2006?
So, what does all this portend for the upcoming hurricane season? It is well-known that the presence of a La Niña usually means more Atlantic hurricanes, and stronger hurricanes, too. This is because the large-scale wind circulation that develops during a La Niña keeps wind shear levels relatively low over the main development region for hurricanes in the tropical Atlantic. So, the demise of La Niña is good news for those of you living in Hurricane Alley. However, before we get too cheerful about this, it is worth remembering that the unbelievable Hurricane Season of 2005 occurred in El Niño-neutral conditions, and El Niño-neutral conditions are expected for this hurricane season, too. So, let's look at some other factors that will influence this year's hurricane season.

Figure 1. Comparison of this year's May SST anomalies with last year's. Image credit: NOAA.

SST comparison--this year vs. last year
Let's compare last year's SST anomalies (the difference in temperature between observed and normal) with this year's, to see how things have changed (Figure 1). The key things to look at are the SSTs in the Caribbean and the tropical Atlantic between Africa and the Antilles Islands, since this is where 85% of all major hurricanes form. While SSTs are .5 to 1.5 degrees above normal--which is a lot!--SSTs are a full degree Centigrade cooler this year than last year at this time. This reduction in SSTs should keep this year's hurricane season from producing early major hurricanes, like Dennis and Emily of July 2005. However, once we enter the prime hurricane months of August through October, expect another above normal year for hurricanes and intense hurricanes. My worst-case scenario for 2006 is a year similar to 2004, which was awful, but modest compared to 2005. My best-case scenario is a year like 1995, which was still very active, but the Bermuda High set up much farther east and recurved most storms before they hit land. Of course, this would be bad for the northeastern Leeward Islands, which got pounded in 1995.

The Gulf of Mexico SSTs are much warmer this year than last, due in part to the record warm temperatures the U.S. experienced in January and April. This may allow for more intense that normal June systems to develop in the Gulf this year. However, remember that systems that develop in the Gulf usually only last a day or two, which doesn't give them much time to strengthen before they hit land. There has only ever been one major hurricane in June (Audrey of 1957).

The other item of interest is that the pattern of SSTs over the eastern Pacific is much different this year versus last year. Waters near the Equator were much warmer last year, thanks to the lingering effect of the El Niño event early in the year. There is also a much warmer pool of water north of Hawaii this year. These differences may end up having a significant influence on this year's jet stream pattern, and where the Bermuda high ultimately sets up camp. The jet stream and Bermuda high determine how hurricanes are steered, but unfortunately we don't know enough about long-range influences of unusual SST patterns on the weather to be able to predict where this year's hurricanes are likely to be steered. The bottom line is that SSTs are cooler and have a much different pattern this year compared to last year, and thus we should not expect a continuation of last year's ridiculously hyperactive, once-in-a-lifetime hurricane season.

Outlook for the rest of May
SSTs are already warm enough to support hurricane formation in the Gulf of Mexico, and the entire tropical Atlantic. What is saving us are the strong upper level winds of the jet stream, which has been dipping far to the south and creating lots of wind shear. The jet stream is forecast to remain active and fairly far south for at least the next two weeks, which should maintain unfavorable levels of wind shear over the Atlantic for the remainder of May. As long as we're talking about tornado outbreaks in the southern U.S., such as we've experienced this week, we don't have to worry about hurricane formation in the Gulf of Mexico. Tornado outbreaks require a stong jet stream, which is the bane of a hurricane trying to form.

The other missing ingredient--at least in the Caribbean and tropical Atlantic--has been the lack of an initial disturbance to get a hurricane started. Africa has just begun to produce its usual summer parade of tropical waves, which frequently serve as the nucleus for a tropical storm. These tropical waves are coming off of Africa at about 2 degrees North Latitude, which is too close to the Equator to allow a hurricane to spin up. I'm not expecting any tropical development for the rest of May in the Atlantic due to high wind shear and the lack of proper initial disturbances.

It's another story in the Eastern Pacific, where wind shear is less and the remains of an old cold front coming off of North America could serve to trigger tropical storm formation as early as next week. The hurricane specialists at the National Hurricane Center begin rotating shift work on Monday May 15, which marks the official beginning of the Eastern Pacific hurricane season.

My next blog will be on Monday. I'll talk about air pollution some next week, since May marks the beginning of air pollution season, and next week is EPA's Air Pollution Awareness Week.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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613. TheSnowman
1:14 AM GMT on May 15, 2006
Colby Your Famous with your own Website!!!! Awsome man I never knew
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612. louastu
1:16 AM GMT on May 15, 2006
150 mph is considered a super typhoon.
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611. ForecasterColby
1:07 AM GMT on May 15, 2006
The right-front is the strongest in the northern hemisphere, the left-front is the strongest in the southern hemisphere.

Chanchu is on the borderline for supertyphoon status, I know >150mph is a supertyphoon, but I don't know if 150mph is considered one.

That visible looks superb.

For all you new people around, take a look at my site (www.theahc.webhop.net), and the thread for Chanchu here.
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610. louastu
12:53 AM GMT on May 15, 2006
The strongest winds are typically found to the right of the storm track. In the Northern hemisphere, this is usually the North side or East side of the storm.
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608. DisneyEchoEarRich
12:48 AM GMT on May 15, 2006
In general, is the worst side to be to the east of a super typhoon similar to how usually the worst winds are to the east of a hurricane when it makes landfall in the U.S.?
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607. Weather456
8:34 PM AST on May 14, 2006
from the 8:05pm EDT 14 may atlantic discussion
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606. Levi32
4:14 PM AKDT on May 14, 2006
First visible image of Chanchu of the evening. Click for larger image:

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604. RL3AO
6:58 PM CDT on May 14, 2006
Well, the 2006 Eastern Pacific Hurricane Season is underway. Looks like we might have an early storm. Just 2 weeks until the Atlantic Season starts.
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603. RL3AO
6:56 PM CDT on May 14, 2006
3 minutes until the start of the Eastern Pacific Hurricane Season.
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602. turtlehurricane
11:54 PM GMT on May 14, 2006
im going to try and make a website called hurricane warning that will have information about tropical cyclones around the globe
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601. TampaSteve
11:29 PM GMT on May 14, 2006
Chanchu will landfall as at least a solid Cat 4. Hong Kong better get ready!
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600. turtlehurricane
11:32 PM GMT on May 14, 2006
im looking at all the models now and theres a large cone of error from taiwan to hainan
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599. LemonAromatique
11:21 PM GMT on May 14, 2006
Hmm. That is a rather interesting GFS for it. Yea, the weather channel is beginning to run some brief segments on it, which usually means they find it pretty significant (of course, it is).
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598. squeak
6:21 PM CDT on May 14, 2006
Regarding the windfield, it has has been steadily expanding all day.
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596. hurricane23
7:02 PM EDT on May 14, 2006
hey guys ive also been tracking this incredible typhoon on the pacific...here the forcast from hurricane alley!

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595. RL3AO
6:05 PM CDT on May 14, 2006
I'm not sure when the first TWO is issued.
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594. ForecasterColby
11:01 PM GMT on May 14, 2006
I think Chanchu might be able to hold its eyewall. It certainly doesn't look too bad ATM.
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592. RL3AO
6:02 PM CDT on May 14, 2006
57 minutes until the start of the East Pacific Hurricane Season!
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590. hurricane23
10:52 PM GMT on May 14, 2006
hey guys iam trying to post but it wont let me.
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589. tornadoty
10:53 PM GMT on May 14, 2006
I think that Chanchu will probably
a) Start or be going through an ERC or
b) Weakening due to dry air entrainment at landfall. I expect a 115kt landfall, but with an expanding windfield, much like Katrina, that could produce a massive storm surge that could devastate Hong Kong.
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588. RL3AO
5:53 PM CDT on May 14, 2006
Hello hurricane23.
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587. hurricane23
10:51 PM GMT on May 14, 2006
hey guys whats up iam new here!
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586. tornadoty
10:50 PM GMT on May 14, 2006
It's size and structure quite remind me of Hurricane Floyd.
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585. ForecasterColby
10:31 PM GMT on May 14, 2006
Oooookay, that wasn't the image I was trying to post.

More like 5-6nmi from that one.
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584. ForecasterColby
10:19 PM GMT on May 14, 2006

On IR/Visible imagery, Chanchu's eye looks small, but it's actually rather large. I'd estimate 11-12nmi from this image.
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583. Levi32
2:12 PM AKDT on May 14, 2006
Central Atlantic visible loop shows that our little wave approaching the Caribbean still has a little spinning feature associated with it. It could still be something to watch if it gets some convection going when it enters a low shear environment.

I have to run for an hour or so. I'll be back then!
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582. Levi32
2:08 PM AKDT on May 14, 2006
Yep with that spin and look it had a couple days ago, it wouldn't have taken much time to turn warm core and then we would have been in trouble. Only I don't think there would be any way for it to get into the gulf in the middle of summer. Maybe the gulf stream but the trough would still have to dig pretty far south to get a system like that over water.
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581. StormJunkie
10:03 PM GMT on May 14, 2006
Yea Levi, especially if it had looked as good as it did when it was over the lakes. Just can't help thinking about it with that well defined spin. Could that system, with a little different conditions, have pushed due south and in to the Gulf or SE and out ove the Gulf Stream


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580. Alec
6:04 PM EDT on May 14, 2006
lol turtle...I would have hated to hear they went out to sea!
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579. turtlehurricane
10:02 PM GMT on May 14, 2006
ya, they burrowed in deep.
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578. Levi32
2:00 PM AKDT on May 14, 2006
Oh ok SJ sorry. That could be nasty if it was over tropical waters.
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577. Alec
5:59 PM EDT on May 14, 2006
I bet they were doing a bit more than just "hissing" when Wilma was threatening S FL...
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576. StormJunkie
9:58 PM GMT on May 14, 2006
Levi, I was actually talking about the whole system. The Great Lakes system.

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575. Levi32
1:58 PM AKDT on May 14, 2006
Just imagine what it would be like if Chanchu was forecast to be strengthening upon landfall. I don't want to think about it.
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574. turtlehurricane
9:57 PM GMT on May 14, 2006
lol, yup. no hissing yet this season though
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573. turtlehurricane
9:56 PM GMT on May 14, 2006
did any of u guys see taht discovery channel thing about wat if hong kong was hit? this whole situation seems eerily similar to the show
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572. Alec
5:56 PM EDT on May 14, 2006
so turtle, you still have your "hissing" turtles?lol
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571. Levi32
1:54 PM AKDT on May 14, 2006
Yeah SJ I see what you mean. If that tail end of the cold front was over the gulf with low shear and touched off that convection, we might be looking at something tropical.
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570. Weather456
5:51 PM AST on May 14, 2006
MANILA, Philippines (Reuters) -- The death toll from Typhoon Chanchu rose to 32 in the Philippines on Sunday, after more bodies were found from a capsized boat, and officials said the storm had affected or displaced more than 42,000 people.
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569. turtlehurricane
9:53 PM GMT on May 14, 2006
The Joint Typhoon Warning Center has set the initial intensity at 130 KNOTS as of Warning #25. Based on JTWC's intensity, Chanchu is now a SUPERtyphoon.-----courtsey of independentwx
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568. StormJunkie
9:50 PM GMT on May 14, 2006
well that did not work. and levi beat me to it with a much simplier explination then I was going to give.

This system over the US is impressive. Spurred hail storm in my area. Imagine if it got over warm water and low shear, then changed over. Ouch. Not that this could or will happen, just something I thought about.

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567. Levi32
1:50 PM AKDT on May 14, 2006
Weather456 a super typhoon has sustained winds of over 150 M.P.H. Chanchu has winds of 150 so she is basically a super typhoon but until she reaches 155 they won't lable her as such.
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566. turtlehurricane
9:50 PM GMT on May 14, 2006
thanks storm and levi
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565. turtlehurricane
9:50 PM GMT on May 14, 2006
o ok, just html
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564. Weather456
5:41 PM AST on May 14, 2006
Is Chanchu a Super typhoon?
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563. turtlehurricane
9:48 PM GMT on May 14, 2006
i see restriction in the north quadrant
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