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ENSO Monitoring - A La Niña to boost the tropical season ?

Alexandre Aguiar

ENSO Monitoring - Pacific already in La Niña mode

Dear Friends

Here is the latest ENSO Diganostic Discussion from NOAA from January 11 (so 20 day ago to be fair):

Synopsis: El Niño conditions are likely to continue through March-May 2007.

Here is the Australian BOM bulletin released today (January 31):

  • Equatorial Pacific SSTs have cooled and are close to or below El Niño thresholds.
    [*]Negative subsurface anomalies have strengthened and spread further east along the thermocline and have nearly reached the surface in the eastern Pacific.
    [*]The SOI has a current (29th January) 30-day value of −9.
    [*]Trade Winds have generally been somewhat stronger than average apart from a weakening in the central-west Pacific in the middle of the month.
    [*]Cloudiness near the date-line has recently been above average.
    [*]Most computer models predict the decay of El Niño conditions in the first half of 2007.

If some thresholds for El Niño regions are not met at this time the real time condition of the Pacific is not of a warm phase. If the condition RIGHT NOW do not meet the standards of an El Niño and the phase is not cool, what you would call it ? We call a trend towards neutrality. Here are the anomalies for 01/28:

Nino 1: +0.28C
Nino 2: +0.26C
Nino 3: +0.64C
Nino 3.4: +0.43C
Nino 4: +0.57C

The cooling is ocurring very rapidly. Very soon, maybe still in February, Niño 1+2 will already be in the negative territory. A La Niña in the next moths is a possibility that increases by the day. Check the subsurface cold waters rising in the Pacific:

wkxzteq_anm.gif


The POAMA model two months prior to the El Niño declaration by NOAA in 2006 the POAMA model was not indicating a high percentage of a warm phase. Two weeks ago the model was indicating a July with near 0.5 and an August of 0.6. Now it is negative or near zero all over the first half of the year. The model appears to be behind the speed of the cooling underway and it is running to catch it. Note the first 15 runs (red line) and the trend in the last 15 runs (blue lines):

poama3101om3.jpg


See also NOAA's CFS trend to Niño 1+2 (major player of weather in South America) as the model inticates it will be plunged in very negative territory by March and April.

cfs3101mn7.jpg


Or you can check the FSU climate model:

elnino1.gif


I strongly believe the 2006/2007 El Niño event is basically dead and the question now is how fast a La Niña will start to be discussed in the ENSO climate bulletins by NOAA and the BOM.

We are seriously considering that the fall period (March to June) in South America southernmost areas (Southern Brazil, Argentina, Uruguay and Chile) may figure among the coldest in many years due to the influence of the very negative signal in the Nino 1+2 region indicated by CFS. The NOAA's CFS T2M maps corroborates the idea of an unusual cold autumn in this part of the globe.

It will be very interesting to see the next update from Dr. William Gray considering the shorter El Niño and the faster cooling of the Pacific. We would do not rule out a rise in the number of forecasted storms in the tropical season based on the real time data we see and the trend shown by the models.

Alexandre
 
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The subsurface temperatures are the best guide for forecasting the coming months. I have been noticing this cooling trend for the past couple of months now. As far as the atlantic tropical activity is concerned, no EL-Nino is needed for increased tropical cyclone occurance not so much La-Nina. Bill Grays December forecast has called for the demise of EL-Nino and increased his atlantic numbers. I would expect to see the same numbers in his April and June forecasts. The EL-Nino appears to be breaking down more rapidly than was predicted a few months ago. The 1997/1998 strong EL-Nino event broke down at a rapid rate which allowed in part to make the hurricane season of 1998 an active one.
 
Jim and others

See how fast the POAMA model is cooling the Pacfic. Note the difference between the 30-day running mean of yesterday and today:

poama3101om3.jpg


poama3101bco7.jpg
 
Alexandre, the MEI was updated this past week and you'll be interested to check out the comparison there to '63/'64.

Thank You Margie !! I saw the MEI bulletin earlier in the week. The trend, in fact, is similar to 1963-64. The 1964 season had twelve storms and six hurricanes. All six of the hurricanes strengthened into major (Category 3) storms. Another analogue I am paying attention is 1977/1978 (based in the SSTs), buit is does not offer a good clue to the tropical season as the Atlantic Multidecadal Oscillation was in the negative phase. Now there is the risk of a La Niña and a warm Atlantic at the same time and the result could be another busy season.
 
I am hoping that, like last year, the SSTs don't rise so much, and I will be watching to see if a pattern begins with the huge SAL outbreaks...and the weirdness with the upper level lows and troughing from last year. My big lesson from 2006 was to always "look out the window" and see what patterns are starting to develop. Last year the last half of July set the tone for the rest of the season, so, being friends with a met that was noticing these things early (and so subsequently made a very accurate season forecast update at the end of July -- 9/6/1-2), I learned the value of watching and looking for indications of developing patterns -- also, that many conditions that factor into whether a busy season will occur, really don't set up until the last minute, from what we are able to see with the current state of the science.
 
Where are you getting the CFS data from Alexandre? I'd like to see the Nino 3 and 4 graphs as well. The BoM graph in this case is Nino 3 so the CFS one is a only partly the Nino 3 area.
 
IRI has confirmed this Friday:

"As of mid-February 2007 conditions indicate that the El Niño event has ended. SSTs are currently observed to be approximately 0.5C above average in the parts of the equatorial Pacific, particularly near the dateline. In the ENSO relevant regions of the central/eastern equatorial Pacific SST anomalies have declined considerably since their peak values in December 2006. Cold SST anomalies have developed in the eastern Pacific, reaching approximately -1.0C below average near 125W. The deep, or downward, thermocline perturbations in the eastern Pacific, associated with the El Niño event, have been replaced over the past month with shallow anomalies. The upwelling Kelvin wave associated with the shallow thermocline anomalies originated in the off-equatorial western Pacific, and has been slightly amplified by large-scale easterly wind anomalies since late December. These easterly wind anomalies are also helping to draw these subsurface temperature anomalies toward the surface, resulting in the localized cold SST anomalies. Currently the thermocline is shallower than normal across most of the equatorial Pacific, and the Trade Winds have been anomalously easterly".

You can read the entire bulletin at:

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html
 
The Australia Bureau of Meteorology also declared the end of the El Niño episode. Now only the NOAA remains indicating "weak El Niño conditions". Here is the latest BoM bulletin:

CURRENT STATUS as at 21st February 2007

Next update expected by 7th March 2007 (two weeks after this update).

Summary: The 2006/07 El Niño has ended

The 2006/07 El Niño has ended. All the main ENSO indicators show that neutral conditions have returned to the Pacific Basin. Along the equator, sea-surface temperatures are cooling rapidly and have been below their El Niño thresholds for about a month now. The Trade Winds have mostly been close to or somewhat stronger than normal since December, the SOI has been neutral for three of the past four months and central-western Pacific cloudiness is close to average. Computer models indicate further cooling in the Pacific, with a La Niña not out of the question (see third paragraph).

What does this mean for Australia? Firstly, while the end of the El Niño would normally be associated with a return to more normal rainfall patterns, it should not be seen as a precursor to drought-breaking rains. This particularly applies to water supplies in parts of eastern and southern Australia, which in some instances require several years of healthy rainfalls to recover to a satisfactory level. Nonetheless, we can be cautiously optimistic that there will be a general easing of dry conditions in drought-affected areas over the next one to two seasons.

A La Niña in 2007?

The chance of a La Niña developing in 2007 is thought to be higher than the long-term average (which is about one in five or 20%) because (a) they have a tendency to follow an El Niño; (b) the El Niño has decayed somewhat earlier than normal thereby giving time for a La Niña to begin developing during the critical March to June period; and (c) a large pool of cold sub-surface water has developed in the central to eastern tropical Pacific Ocean. La Niña events are generally associated with wetter than normal conditions across much of the eastern half of the country from about autumn.
 
Last December we for the first time released our own forecast for a hurricane season in 2007. It was our first attempt. In the bulletin relesead by us on December 6th and published on our site on December 7th, one day before Dr. Gray's forecast, we indicated 14 storms, 7 hurricanes and 5 major. In the following day Gray's forecast was 14 storms, 7 hurricanes and 4 major. The most important. We indicated the risk of a La Niña developing during 2007 in time to affect the hurricane season. Well, NOAA is finally indicating the chance of a La Niña and is considering its impact in the North Atlantic tropical season.

La Nina could provide favorable conditions for hurricanes

By Ken Kaye

South Florida Sun-Sentinel

(MCT)

FORT LAUDERDALE, Fla. - La Nina, an atmospheric condition that promotes the formation of hurricanes, might be back in time for this year's six-month Atlantic storm season, government forecasters said Tuesday.

The weather pattern, the result of a cooling of the equatorial Eastern Pacific Ocean, acts to calm the atmosphere, allowing hurricanes to form uninhibited.

Though its return isn't altogether certain, satellite images and readings from ocean buoys indicate water temperatures in that Pacific region have rapidly decreased, National Oceanic and Atmospheric Administration officials said.

"Although other scientific factors affect the frequency of hurricanes, there tends to be a greater-than-normal number of Atlantic hurricanes ... during La Nina events," NOAA Administrator Conrad C. Lautenbacher said in a statement.

Meanwhile, the condition's counterpart, El Nino, a warming of the Eastern Pacific, is fading, NOAA officials said. El Nino tends to tear storms apart by creating high-level wind shear. It was credited in part with making the 2006 hurricane season so uneventful.

La Nina commonly comes on the heels of El Nino and can stick around for up to three years, said Vernon Kousky, a research meteorologist at NOAA's Climate Prediction Center in Camp Springs, Md.

That happened from 1998-2001, helping to make each of those years stormier than normal, officials said. If there is a bright note, La Nina conditions that develop between March and June - as this one appears to be doing - usually don't reach peak intensity until the following December, Kousky said. That means the condition might not be fully in place during the June-November hurricane season.

Noted storm prognosticator William Gray of Colorado State University and his research assistant, Phil Klotzbach, have predicted 14 named storms, including seven hurricanes in 2007.

That would represent a slightly busier than normal season, which typically sees 11 named storms and six hurricanes. However, Gray's forecast was drafted in December before the La Nina conditions were detected. Gray's forecast was over-inflated last year because, he said, he didn't foresee El Nino's arrival.

NOAA will release its seasonal outlook in May.

Meteorologists picked up the name El Nino ("The Christ Child") from a Peruvian Christmas festival, which celebrated the waters off the coast of that South American country warming at Christmas time. They opted to call the opposite cooling condition La Nina, Spanish for "baby girl."

---

© 2007 South Florida Sun-Sentinel.

Source

You can read also at the NOAA press release.
 
It's nice to see NOAA is finally talking about a developing La Nina in the next few months. Those very cold subsurface water temps have been there for several weeks, so there latest forecast isn't really a surprise. This is especially true thanks to Alexandre's post here over the past while. I think the biggest question is how strong will this cool episode be? Seems to me it has potential to be quite strong if those subsurface waters of -3 to -4C remain in place.
 
One thing to remember that you don't need a La-Nina to make the enviroment more favorable for tropical cyclone formation. Just have no El-Nino or a neutral. 2004 and 2005 are recent examples the pacific ENSO was neutral not a La-Nina.
 
Of course, NOAA will wait for the three-month SST anomalies under -0.5 to establish the threshold for La Niña, but the Pacific is already in a La Niña mode. Check the pictures below of the SSTs in February 3rd. (above) and March 3 (below).

nina03002007pp6.jpg
 
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I continue to agree that we are rapidly heading into a La Nina spring/summer. The only question in my mind is just how strong it will be. The latest models indicate a continued rapid decline in SSTs in the Nino3.4 region through the spring. Even though the mean solution brings us to weak La Nina by the summer, it's interesting that so far the more bullish models have been verifying better and suggest a moderate to strong La Nina going to the summer and fall.

Looking at the subsurface waters, I don't think a moderate to strong La Nina is out of the quesiton. Not by a long shot.
http://www.pmel.noaa.gov/tao/jsdisplay/

I also wanted to point out that based on research done by Dr. Gray at Colorado State, "La Nina increases hurricane activity (in the Atlantic Basin) & it makes it more likely to threaten the U.S. & Caribbean". I couldn't find the actual paper, but through a Google search I found numerous sites with the same quotes from Dr. Gray.

So while it's true neautral ENSO does enhance the hurricane season, La Nina does a bit more, and more importantly it actually increases the likelyhood of U.S. landfalls. That makes me wonder if the strength of La Nina correlates to anything, or whether it's strengthening or weakening during the hurricane season.


nino34SSTMon.gif
 
As long as we have no El-Nino the chances are the tropical season across the atlantic basin should be above average in number and intensity. I've seen so, so seasons in La Nina years and real active during neutral years. The question on where they track all depends on where the longwave trough's and ridges setup toward the latter part of the summer. If the dreaded Hudson Bay vortex is in place which is there more than not. The majority of the atlantic tracks will be east of the U.S. coastline much like 1995. If we have a setup like 2004 and 2005 which are not very common the main trough will favor the western U.S. which would allow tracks into the southeastern coastline and Gulf coast.
During neutral and La-nina years the are many more hurricane tracks across the Caribbean sea.
 
As long as we have no El-Nino the chances are the tropical season across the atlantic basin should be above average in number and intensity. I've seen so, so seasons in La Nina years and real active during neutral years. The question on where they track all depends on where the longwave trough's and ridges setup toward the latter part of the summer. If the dreaded Hudson Bay vortex is in place which is there more than not. The majority of the atlantic tracks will be east of the U.S. coastline much like 1995. If we have a setup like 2004 and 2005 which are not very common the main trough will favor the western U.S. which would allow tracks into the southeastern coastline and Gulf coast.
During neutral and La-nina years the are many more hurricane tracks across the Caribbean sea.

Is Nino coming back after a relatively little brief La Nina tendence?It would seem it is.

sstanim.gif
 
El Nino's not coming back, but La Nina isn't developing as quickly in the Central Tropical Pacific as I thought initially. It is developing rapidly in the Nino 1+2 region, however, and historically La Nina events develop from that region first and spread westward. Judging by the subsurface waters of -3C to -4C throughout the entire region, La Nina looks to be lurking in the coming weeks. But the above normal pocket of SSTs east of Indonesia and west of the Dateline seems to be keeping the weather pattern more indicative of a decaying El Nino right now (cool Eastern U.S.), even though it's been dead for a while. I would expect to see some big changes develop in the Nino 3.4 region by May.
 
SOI and El Nino/La Nina

With the recent taking of the SOI, there was a pressure difference between Darwin and Tahiti- enough so that perhaps a brief westerly wind burst will set up and stunt the growth of this La Nina. Just a thought since the SOI did plummet for a time recently and is still negative. The longer it stays negative, the more westerly winds would set up- if I understand this correctly.
 
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