La Niña is gone

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

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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

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113. StormJunkie
9:06 PM GMT on May 11, 2006
Intresting K8eCane. You got anymore info on that one. Right up the road from me.

And yes Creg, today is the closest approach for some chunk of the commet +- the 11hr thing. Don't wory though, I think that someone has installed a carbon nano tube net to protect us. lol.

SJ
Member Since: Agosto 17, 2005 Posts: 26 Comments: 15634
112. StormJunkie
9:02 PM GMT on May 11, 2006
Recap of katrina on the National Geographic Channel. They are going over the infamous, Stormtop predicted S movement across Florida now.
Member Since: Agosto 17, 2005 Posts: 26 Comments: 15634
111. K8eCane
8:54 PM GMT on May 11, 2006
has anyone ever heard the legend of the grey man ?..took place at Pawleys Island SC many many years ago...but as the legend goes, he appears now and then...appeared to a couple before Huricane Hugo
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110. Cregnebaa
3:49 PM EST on May 11, 2006
Just had a thought, didn't some one say we were going to be hit by a comet today?
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109. TheLuckyTacoBlizzard
1:23 PM PDT on May 11, 2006
i think may be tx this year
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108. ForecasterColby
8:20 PM GMT on May 11, 2006
I will say this - I think Dr. Masters will be eating the 'worst case 2004' words later on. It may not be 2005-scale, but I'd say it'll throw '04 right out the window. 2004 was Florida's year, 2005 was the northern Gulf Coasts, who's to say 2006 won't be Houston's?
107. ForecasterColby
8:19 PM GMT on May 11, 2006
I stand corrected. I thought the synoptic-scale system was also called a mesocyclone. *shrugs* Still impressive, whatever one calls it.
105. StormJunkie
8:14 PM GMT on May 11, 2006
Afternoon all and welcome NolaNC. Nice discussion on the ITCZ. As for the storms it is only a matter of time. I say give or take a week from the offical start. June 1.

Anywho I am diligently working to update the content on StormJunkie.com. There are aready some very good links there, and I have many more to go through. Ya'll let me know what you think in my blog.

Thanks
SJ
Member Since: Agosto 17, 2005 Posts: 26 Comments: 15634
104. Alec
4:17 PM EDT on May 11, 2006
darn mistyped my last post....lol Yes agree w/you Colby....gotta treat articles carefully...well im off, have a great afternoon guys:)
102. Alec
4:10 PM EDT on May 11, 2006
Hey Colby, i noted that...(the fact that the ITCZ moves north and south) The article I found, said their definition of the ITCZ in a weird way...
101. CFLweather
7:48 PM GMT on May 11, 2006
Its normal for the waves coming off of Africa to be too far south to support tropical development this time of year. This mimics last years hurricane season, there was a few impressive waves around 3-6N in May of 2005 but none formed into a tropical system.

The SST's are a concern, especially in the Gulf. It will be interesting to see what the SST's are in the peak of this years hurricane season. I can only assume it will be as high if not higher than last year. This is a scary thought now that we have seen how quickly a cat 1 hurricane can turn into a 890mb hurricane.

The record high temps in the US are obviously a sign that the SST's in areas that can support warm water (26+ celsius) are going to warm MUCH more than normal. This is going to be another worst case scenario if the shear levels die off surrounding the US, and the Bermuda High manages to push everything in the open atlantic due West.

2004 was a horrible hurricane season, and I will never forget it because I was hit dead on by numerous hurricanes. 2005 hurricane season was something that has never happened
recorded history. 2006 may eclipse both 2004 and 2005, so please be prepared. Think about, can you honestly say that the 2004 and 2005 hurricane seasons were a coincidence along with all the other worldwide weather events that have been occuring. Not to mention all the warnings we have had from NASA, NOAA, The Pentagon, and numerous other government agencies and brilliant scientists from around the world.
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100. ForecasterColby
8:14 PM GMT on May 11, 2006
It's not a hurricane. That's a mesocyclone, a low that forms when a warm and cold front start to rotate around each other. It is an absolutely stunning storm, though.
98. ForecasterColby
8:07 PM GMT on May 11, 2006
Correct, Alec, but the ITCZ doesn't stay at the Equator as noted above. Storms can form at the Equator with sufficient vorticity already present, but it is exceedingly rare.
97. ForecasterColby
8:02 PM GMT on May 11, 2006
NOLA, you're correct, many hurricanes do form from the ITCZ. Most of those originate in the eastern Atlantic (the ITCZ goes around the world), and track WNW across the Atlantic before recurving around the Bermuda High (usually, as the name suggests, centered east of Bermuda).
96. ForecasterColby
7:18 PM GMT on May 11, 2006
The ICTZ is an area of low shear, easterly winds, and convective activity that moves north and south roughly 15 degrees to either side of the equator.
95. Alec
3:49 PM EDT on May 11, 2006
also the coreolis effect is nill near the equator...(C.E. helps the storms spin)
94. Alec
3:42 PM EDT on May 11, 2006
The ITCZ is where NE and SE trade winds converge which support thunderstorm growth ....thats the short and sweet version...here's the long explanation I found from this site below-

http://www.bbc.co.uk/weather/features/az/alphabet75.shtml

"The ITCZ is the area where the northeast and southeast trade winds, centred on the equator, converge. This convergence forces the very moist tropical air to rise and produce huge cumulonimbus clouds, which can reach up to 60,000 feet, and give some tremendous thunderstorms and rainfall.

This wet zone moves north and south with the angle of the sun, taking the clouds and rain with it. So the Yoruba in Nigeria, have a wet and dry season. In fact, in southern Nigeria there can be two wet and two dry seasons as the ITCZ pushes northwards and then south again.

The wet season starts in March in the south and lasts until July, with another shorter rainy season during September and October. In the north the wet season is usually from June to September with the rest of the year dry, very hot and sunny. It is during the wet season that the large storm clusters move westward and out into the Atlantic on their journey to the Caribbean."
93. HurricaneMyles
7:43 PM GMT on May 11, 2006
Posted By: STORMTOP at 6:53 PM GMT on May 11, 2006.
the temps would not support development yet off the coast of africa...looks very impressive for so early in the year...

Acutally, the temps are plenty warm down there near Africa. Like Dr. Masters said, the whole Atlantic basin is warm enough to support development. The true reason these wont develope is that they are far too close to the equator at around 2-6N. The shear is even pretty low out there, and even though it has happened in other basins, I don't think a storm has ever developed that close to the equator in the Atlantic.

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92. ClwtrChuck
7:41 PM GMT on May 11, 2006
Last year storms seemed to explode in intensity in the waters of the southern Gulf. Can we expect more of the same this year with the elevated SST in the gulf?
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91. NOLAinNC
3:28 PM EDT on May 11, 2006
Alec if you are still around - can you define the intertropic convergence zone for me? Those bubbles/blobs look like future hurricanes to me!
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90. TheLuckyTacoBlizzard
12:19 PM PDT on May 11, 2006
: MichaelSTL i seee look on the photo look like a lot of storms and look at my link and look at the shear down there where the storm are
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88. TheLuckyTacoBlizzard
12:11 PM PDT on May 11, 2006
hmmm now i got to no how to not put my word along with my words in my link
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86. Alec
2:56 PM EDT on May 11, 2006
ITCZ-intertropical convergence zone
85. STORMTOP
6:53 PM GMT on May 11, 2006
the temps would not support development yet off the coast of africa...looks very impressive for so early in the year...
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84. NOLAinNC
2:54 PM EDT on May 11, 2006
What is ITCZ?
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83. Levi32
10:52 AM AKDT on May 11, 2006
The MJO is in Phase 1 which corresponds to Africa and the Atlantic so that is probably why there is increased convection at the ITCZ.
Member Since: novembre 24, 2005 Posts: 635 Comments: 26547
82. Alec
2:51 PM EDT on May 11, 2006
you are perfectly correct Michael....for the short term it "modifies" and may actually decrease the SST temps but that may help in the long term create a deep heat content...
81. Levi32
10:50 AM AKDT on May 11, 2006
My gosh Colby just wait till that all comes north!
Member Since: novembre 24, 2005 Posts: 635 Comments: 26547
79. ForecasterColby
6:47 PM GMT on May 11, 2006
NOLA, it cools by evaporation, whether fueling a hurricane or not.

Syke, Accuweather predicted a major New England hurricane for the year, and for some arcane reason the media worships Accuweather.

And...can you say 'cape verde'?



That's some serious ITCZ!
78. Alec
2:44 PM EDT on May 11, 2006
NOLA, the cooler air temps(which are forecasted the next 5 days for the Gulf coast) help to stop dramatic heating and may pull down the SST a little bit...Water is much more efficient at storing the sun's heat energy than land....that's why ocean temps dont drop as quickly as land temps do.....large waves also help upwell cooler water(if the warm layer is thin)
77. NOLAinNC
2:46 PM EDT on May 11, 2006
Holy Moly!
We just got a huge wind gust here in the mountains out of nowhere! I guess a front has arrived. Look out Piedmont!
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76. Alec
2:43 PM EDT on May 11, 2006
a ton OF* energy...sorry for my typos:(
75. NOLAinNC
2:42 PM EDT on May 11, 2006
Alec - that is a scary thought. Are there other ways that heat can disapate from the Gulf?
-NOLA
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74. Skyepony (Mod)
6:26 PM GMT on May 11, 2006
yeah, look it how anomusily warm it is up toward the New England area. Is that why the media has been pushing the NE to be ready? It's the only indicator that I've seen for the warning.
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73. Levi32
10:41 AM AKDT on May 11, 2006
Colby thank you for clarifying what "Chanchu" is. Interesting they would give a storm a name that is an "it".
Member Since: novembre 24, 2005 Posts: 635 Comments: 26547
71. Alec
2:37 PM EDT on May 11, 2006
that is exactly why if the Gulf doesnt see any storms till Aug/Sept there will be a ton heat energy stored in there(with depth) Hope then, that a huricane doesnt get in there...
69. TheLuckyTacoBlizzard
11:40 AM PDT on May 11, 2006
Posted By: TheLuckyTacoBlizzard at 11:39 AM PDT on May 11, 2006.
hmmm where my post go from be for i was only asking hmm a ? was it some in i said


for get that post i this did i see it now
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68. TheLuckyTacoBlizzard
11:38 AM PDT on May 11, 2006
hmmm where my post go from be for i was only asking hmm a ? was it some in i said?
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67. TheLuckyTacoBlizzard
11:36 AM PDT on May 11, 2006
Jeff Masters


oh i fro got to ask you how march hoter is the gulf from this time last year

this is david how you like my new ID?
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66. TheLuckyTacoBlizzard
11:34 AM PDT on May 11, 2006
Jeff Masters

got a ? if a hurricane get in the gulf could it go right in to a cat 5 hurricane and do you think a hurricane will make land fall as cat 5 this year?
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64. NOLAinNC
2:32 PM EDT on May 11, 2006
Thanks Dr. Masters!
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63. ForecasterColby
6:31 PM GMT on May 11, 2006
Personally, I'd say we're still in a weak La Nina. But given that this Nina should never have developed in the first place, STORMTOP, the SPC, Dr. Masters, and myself are all in uncharted waters.

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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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