Watching El Nino

By: Levi32 , 4:52 PM GMT on February 08, 2007

Hurricane season is only 3 months away, and like any year, the SSTs in the equatorial Pacific play a huge role in what the season will be like. Last year El Nino was partially responsible for the unexpected low number and intensity of storms. There has been an El Nino since last summer and through this winter, but there are signs of it weakening. The latest official update from Australia reflects this, and I encourage you to read it as it has some interesting information. Here are some maps and charts:

30-Day SOI (Southern Oscillation Index):



Here is a link to a 3-year chart with a brief explanation of the SOI.

SSTs and anomalies in the equatorial Pacific from the surface to 500 meters deep:



Near 125w at about 100 meters you can see a good-sized ball of cold water moving closer and closer to the surface in the anomaly map(bottom chart) over the last couple months. If this cold water does make it to the surface SST anomalies will go down dramatically. Also notice the cold water bulging upward towards the surface in the SST map (top chart). This is the area of cold water shown in the anomaly map above. This could be evidence of upwelling, which is bringing colder water up from the deep ocean closer to the surface.

Global SST Anomaly Map:



Experimental seasonal forecast models are all showing some sort of trend toward La Nina in their SST forecasts, some more dramatic that others. These same models are also forecasting precipitation patterns this summer which correspond to a La Nina pattern.

All these signs point to a weakening El Nino, and I think a La Nina could be in the making by the beginning of the hurricane season. Of course there's no way to tell how strong it will be, or exactly what impacts it will have. Predicting El Nino and La Nina is one of the toughest aspects of forecasting.

We shall see what happens!
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What is El Nino?

El Nino is a reversal of the normal trade wind flow over the equatorial Pacific. When conditions are normal, trade winds flow from east to west. This usually sets up high pressure over northwestern South America, and low pressure in the western Pacific near Australia. A normal rainfall pattern with moist in Australia and dry in the eastern Pacific and South America is the result.

However when El Nino pops up, those trade winds can be reversed or greatly slowed down. The flow is then from west to east, which sets up the low pressure over NW South America and the high pressure over Australia. This is the total opposite of normal conditions. If El Nino sticks around for several months, Australia experiences severe droughts, and NW South America experiences heavy tropical rains. SSTs in the eastern equatorial Pacific are warmer than normal because no upwelling is occurring due to the reversed trade winds. Upwelling is brining up colder water from the deeper ocean to the surface. When the trade winds are from the east like normal, they "push" the ocean water westward from the coast of South America. As the warm surface water is pushed westward, the cold water from deep down moves up to replace it in response. But when the trade winds are reversed, upwelling is shut down, and the SSTs near the South American coast are warmed greatly. Warming of the SSTs near the equator is one of the first signs of an El nino, and is an easy signature to recognize on an SST anomaly map. El Nino is also known to cause global weather pattern changes which can be very severe. Where I live in Alaska, El Nino causes winters to be extremely mild and rainy, and summers to be very hot and dry. The affects are different for different parts of the world.

El Nino also has a large impact on the Atlantic and eastern Pacific Hurricane seasons. Warming of the SSTs in the eastern equatorial Pacific tends to be counter-acted by a cooling of the SSTs in the Gulf of Mexico, the Caribbean, and the western Atlantic. It also tends to increase wind shear. This lowers the average intensity and number of hurricanes. A classic example is last year, when even a weak El Nino greatly reduced the number and strength of hurricanes. The affects of El Nino can reduce the number of U.S. hurricane landfalls as well. When low pressure sets up over NW South America, high pressure sets up over the Caribbean, which directs tropical waves south and west over South America. These waves then pop out on the other side in the eastern Pacific, where they have a much better chance to develop. This results in a much more active eastern Pacific hurricane season. Therefore El Nino decreases hurricane activity in the Atlantic, and increases activity in the eastern Pacific.

La Nina is the opposite of El Nino, and is simply an intensification of normal conditions. Easterly trade winds are stronger, which causes more upwelling of colder deeper water in the eastern equatorial Pacific. SSTs are colder than normal, which is the signature of a La Nina on an SST anomaly map. Rainfall in Australia is increased, and NW South America experiences very dry conditions. La Nina, like El Nino, also has major impacts on weather patterns across the globe, though usually the opposite of El Nino. Likewise the affects on the eastern Pacific and Atlantic hurricane seasons are opposite. Strong high pressure builds in the eastern equatorial Pacific, which results in low pressure over the Caribbean. Tropical waves in the Atlantic are steered northwest towards the U.S. and Mexican coasts, increasing the number of storm landfalls. The cooling of the SSTs in the equatorial Pacific also tends to warm the SSTs in the western Atlantic. Wind shear is also decreased. This results in a more active Atlantic hurricane season. On the other end the eastern Pacific sees very little tropical activity, as SSTs are lowered and few tropical waves make it across into the pacific basin.

El Nino and La Nina are some of the toughest pieces of the weather to forecast. Either one could pop up any time without us foreseeing it. However lots of research is being put into these phenomenon, and hopefully some day we will be able to accurately predict these climate-changing events.
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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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42. Skyepony (Mod)
8:43 PM GMT on February 11, 2007
LOL~ it was from your link you left atmos in this post..

Posted By: Levi32 at 5:25 AM GMT on February 09, 2007.

Perhaps you don't live in GMT? (atleast here)
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41. Levi32
8:09 PM GMT on February 11, 2007
Wow that is a nice page Skye thanks! I don't quite understand what you were saying about a 5:25am comment link, but thanks for finding that page on the CDC site. That site is sure loaded with all sorts of good stuff.

Hey ryang!
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40. ryang
7:52 PM GMT on February 11, 2007
Hey Levi.
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39. Skyepony (Mod)
7:41 PM GMT on February 11, 2007
Levi~ that 5:25am comment link, the MJO area in there was awesome. Most complete I've seen yet. Even has the square plot
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38. Levi32
7:15 PM GMT on February 11, 2007
Warm January in the east points to weakening El Nino:

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37. Levi32
9:08 PM GMT on February 09, 2007
As I suspected the upgraded TC Enok to 50 knots. Link
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34. Levi32
6:22 PM GMT on February 09, 2007
Hey here's something interesting:



Ever seen a 40-knot storm with an eye-wall? It can be seen on satellite as well.
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33. Levi32
5:35 AM GMT on February 09, 2007
Did I even give you the right link? LOL I forgot to get the first one in code when I wrote it lol. I guess the second link turned out to be better. Anyways you just click on experimental seasonal foreecasts from the home page and you're there lol. Glad you like the link! Hope it serves your purposes.
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31. atmosweather
5:27 AM GMT on February 09, 2007
Thanks Levi! That'a actually a better link than the one I had originally! I think the one I lost was from the UK Met Office, but I can't find the page on the site. Anyway, your link is better!
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30. Levi32
5:25 AM GMT on February 09, 2007
Hey Rich, about the link you said you lost:

This link is from the CDC site you and Skyepony were getting addicted over lol. It's experimental seasonal forecasts, which show anomaly and probability maps for several different variables. It's not quite what you had before I'm sure, but it's the closest thing to it out there I think. If you or I spend more time exploring the whole site (which might take me months lol) I'm sure we could find some even better maps. Here's another map homepage from the site to get you started so you don't get lost lol!

Goodnight, see you later,

Levi
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27. Levi32
4:27 AM GMT on February 09, 2007
Thanks so much Rich! I really appreciate that :)

Yeah the way that cold water is coming up La Nina could definately be in the books before hurricane season starts. I would be very interested to know where you got those steering forecasts. That's too bad you lost the bookmark. The only place I can even think of getting that sort of stuff is on Accuweather Pro, which (don't tell Bob) I subscribe to. That is interesting that they would be forecasting a more west-positioned Bermuda high. I would actually agree with that based on how the seasonal pattern is setting up, though of course it's too early to draw any conclusions.

I think you're right 2007 will be one rough and intriguing challenge for us! I can't wait either. Hopefully I'll be able to start getting on more as we inch closer to the start of the hurricane season. As you may have noticed I already switched my Alaska weather updates to my other handle, and this blog is now about the tropics again for the summer. Hope to see you around more Rich! I know we definately will after June 1st! I'm sure you will be a very valuable asset this hurricane season as you always have.

Hasta luego mi amigo. Buenas Noches.
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25. atmosweather
4:01 AM GMT on February 09, 2007
Hey Levi, what a blog! Awesome stuff! And I would have no problem with you outrightly posting a prediction of a La Nina for this summer, because I would totally agree. In fact, if you look at the latest 30 day SST anomalies below the surface in the equatorial Pacific and then look at the upper level wind patterns in the tropical Atlantic, I expect ENSO-neutral conditions as early as the end of the month. Actually, I think La Nina will develop BEFORE the start of hurricane season! I don't think it will last long (a recent trend in the ENSO pattern along with the SOI has been to fluctuate a little more drastically over the past few years compared to the previous 30-40 years), but it should be enough to impact the East Pacific and Atlantic Hurricane seasons. But, as we keep finding out, we don't know to what extent, and in what ways!

One intersting thing that I found a few days ago that I somehow lost the bookmark for...a long range forecast for steering currents in the tropical and subtropical Atlantic for the summer months. It seemed to indicate a stronger and more westerly positioned Bermuda High (likely due to the forecast weak La Nina developing at that time), which would analogue 2007 with 2004 and 2005 in terms of where tropical cyclones could track (the Florida east coast, the Caribbean, and the Gulf coast). Naturally, a forecast such as this has a considerable error margin, so there is no way to draw any conclusions from it, but it is very interesting. Add that with NOAA's prediction of a 60% chance that 2007 will be the warmest year on record globally (and supported by an astonishing 1.71 C above average anomaly for the Northern Hemisphere in January, the largest such in history!), and it looks like 2007 will be another busy year for us weather folk! I can't wait for the ride!

Once again, fantastic blog, and I hope you can return here regularly very soon, you are definitely one of the site's "most valuable players".

Take care my friend,

Rich
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24. Levi32
1:12 AM GMT on February 09, 2007
Yeah, but it's impossible to tell what a La Nina will do to the hurricane season. Sometimes it has no affect whatsoever. Other times it really jacks things up.
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22. Levi32
1:03 AM GMT on February 09, 2007
Hey GR! Long time no see to you too! I agree La Nina by July is possible. I can't wait to see what affects that might have on the SSTs in the Atlantic.
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20. Levi32
1:00 AM GMT on February 09, 2007
I'm relieved Bob LOL. Yeah who knows what the heck the ENSO or the hurricane season is gonna do this year. By the way, just a little advice, I don't think many people will think you know what you're doing if you make your forecast the day the season starts lol!

Hey Mark :) Long time no see. Good point about CA. Yeah this El Nino was never really that strong. Then again we havn't had a strong Nino or Nina since the 1998 El Nino. Could bode bad for this upcoming hurricane season.
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19. GetReal
12:59 AM GMT on February 09, 2007
Levi I finally had a minute to stop by, and your blog header caught my eye. I do agree with you that El Nino is rapidly fading away, and will not be a factor for this upcoming hurricane season. In fact I am also leaning towards believing that we will in fact a La Nina event in the EPAC come late July. It may be another interesting season, but no unofficial forecast for 2007 just yet!
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18. DenverMark
12:34 AM GMT on February 09, 2007
Hi Levi :)
I think El Nino is dying out...may transition to La Nina rather quickly. This El Nino never really produced the typical weather. Southern California has been bone dry while the Pac NW got pounded, etc.
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17. weatherguy03
12:29 AM GMT on February 09, 2007
Not me Levi!!..LOL Nah, I agree with that. It makes sense, but the way the ENSO has behaved recently, who knows!..LOL I will make my Hurricane forecast on June 1st!!..LOL
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16. Levi32
12:07 AM GMT on February 09, 2007
Yes Michael I see what you're saying. Yeah I would say we have a good chance of a La Nina too. In fact to tell you the truth I would have said so in my blog entry, however I have a tendency to exaggerate and Bob(weatherguy03) would be all over my case if I did it again lol. If a La Nina does indeed form, I think we can safely say that there's a good chance we'll have a more active hurricane season than last year.
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13. Levi32
5:56 PM GMT on February 08, 2007
How much snow did they have before this event started? I find it hard to believe that they had no snow before now.
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12. Tazmanian
5:55 PM GMT on February 08, 2007
Levi32 but 7ft in olny a few days time they are makeing up there lost time with snow fall
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11. Levi32
5:49 PM GMT on February 08, 2007
And right now they're on the back side of a storm which is producing strong NW winds over the lake, which is probably the cause of all that lake-affect snow the last few days.
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10. Levi32
5:47 PM GMT on February 08, 2007
Well I don't have much experience with New York weather patterns, but from what I can guess it's because they're right on lake Eerie, and they get a lot of lake-affect snow in the wintertime.
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9. Tazmanian
5:45 PM GMT on February 08, 2007
ok why are they geting so march snow in this a few days time???? is this odd for them
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8. Levi32
5:44 PM GMT on February 08, 2007
They have just over 7 feet of snow. 10 feet would be 120 inches, but they have 88 which is 7 feet and 4 inches.
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7. Tazmanian
5:43 PM GMT on February 08, 2007
: Levi32 so they have about 9ft of snow or 10ft?
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6. Levi32
5:42 PM GMT on February 08, 2007
Thanks Bob.
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5. Levi32
5:42 PM GMT on February 08, 2007
Ok well 27 inches is 2 feet and 3 inches. 88 inches is 7 feet and 4 inches. That's a lot of snow!
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4. weatherguy03
5:41 PM GMT on February 08, 2007
Good work Levi.
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3. Tazmanian
5:40 PM GMT on February 08, 2007
Levi32 thy beeen geting snow none stop with and right now they have had 3ft wish is 27.0 inch of snow on and now they have 88.0 wish is about 10ft of snow i think
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2. Levi32
5:38 PM GMT on February 08, 2007
What is the 27? Inches of snow?
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1. Tazmanian
5:37 PM GMT on February 08, 2007
PARISH NY 88.0 1115 AM 2/8

wow 88.0


+

PARISH 27.0 1115 AM 2/8


27.0 they got right now they most have about 11 to 15ft of snow right
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About Levi32

Masters student in tropical meteorology at FSU. Raised in Alaskan blizzards, but drawn toward tropical cyclones by their superior PGF.

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