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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13. GPTGUY
4:02 PM GMT on May 11, 2006
Dr. Masters

Do you think dust from the Sahara will play a factor this year?
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12. JeffMasters (Admin)
11:58 AM EDT on May 11, 2006

Posted By: oriondarkwood (13.13.137.2) at 11:53 AM EDT on May 11, 2006.
From what I read for this and eariler posts (correct me if I am wrong Dr. Masters). Is we will have a later start but during the peak of the season will be some real monsters and the spooky part is the above average chance for rapid intensification cycles near landfall. Specially in the gulf.

This sounds reasonable. I expect at least two Cat 4/5 storms this year. The key is where they will be steered. Hopefully, the Bermuda high will set up farther east, allowing the storms to recurve before hitting land, like happened in 1995. Of course, this would be bad for the Northeastern Leeward Islands, which got pounded in 1995.

Jeff Masters

11. NOLAinNC
11:53 AM EDT on May 11, 2006
Levi,
There are no dumb questions, just the occasional dumb post ;)
I'm curious too.
-NOLA
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10. oriondarkwood
10:49 AM EST on May 11, 2006
From what I read for this and eariler posts (correct me if I am wrong Dr. Masters). Is we will have a later start but during the peak of the season will be some real monsters and the spooky part is the above average chance for rapid intenseification cycles near landfall. Specially in the gulf.
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9. Levi32
7:49 AM AKDT on May 11, 2006
Can I ask a dumb question? is the name "Chanchu" (referring to Typhoon Chanchu) a "he" or a "she".

I don't know Chinese lol.
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8. seflagamma
11:45 AM EDT on May 11, 2006
Dr Masters, thanks for the update and information. I was starting to dance a little jig but then read the rest! Oh well; at leas we are informed.

Appreciate your information! Looking forward to the next blog entry.


Gamma
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7. gcain
3:28 PM GMT on May 11, 2006
Seems like there are two issues: Number of storms and intensity of storms...and while the two are related they are determined by different factors. So really, when we all think about th upcoming season, the questions are, "How many?" and "How intense?" Factors such as temperature probably have more to do with intensity and factors like initial African disturbances has more to do with how many...in a year like 2005 all the factors seemed to be against us...maybe this year it will be one or the other, but not both. At least we can hope.
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6. JeffMasters (Admin)
11:28 AM EDT on May 11, 2006

Thanks for the comments, and I see I needed to add this sentence to the blog:

However, once we enter the prime hurricane months of August through October, expect another above normal year for hurricanes and intense hurricanes.


My thought for a worst-case scenario this year is a year similar to 2004, which was awful, but modest compared to 2005.

Jeff Masters
5. NOLAinNC
11:25 AM EDT on May 11, 2006
I am learning so much from your blogs this year. Thanks Dr. Masters!
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4. weatherguy03
11:20 AM EDT on May 11, 2006
Dr. Masters thank you so much for pointing out SST trends. This has been a big topic of discussion on the blogs for awhile. Thank you for finally sheding some light on the subject.
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3. WSI
3:24 PM GMT on May 11, 2006
He never said this season wouldn't active. He just said the conditions are not as favorable as those where a La Niña is present. Again, as Dr. Masters said, the La Niña conditions where the exact same during the record breaking season last year.
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2. southbeachdude
3:22 PM GMT on May 11, 2006
this is new thinking...everyone else has been talking about a really active season. Thank you for this new research.
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1. haydn
3:18 PM GMT on May 11, 2006
gone? Does this mean that season will be closer to normal?
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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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