ENSO Updates (2007 thru 2023)

[Plant grower]

Hurricane numbers will be back up again on the next forecast in June.

[vbhoutex]

Hurricane numbers will be back up again on the next forecast in June.

Why do you think so?

[HURRICANELONNY]

Yep VB. I don't like when people post a statement with nothing to back it up. I suppose he means that the NCEP forecasts neutral conditions during Hurricane season. While some forecasters are leaning towards El nino towards the second half of the season. I think neutral is a better bet reading the updated NCEP forecast and models.

[Plant grower]

Based on the new information that now neutral conditions will be there for most of the hurricane season. Sorry everyone I though I had made a connection with my statement from the previous post. Another thing to keep in mind is other than Colorado State most other media weather outlets are calling for and active hurricane season, and most of them have the Gulf coast as a target this season.

[Blown Away]

Based on the new information that now neutral conditions will be there for most of the hurricane season. Sorry everyone I though I had made a connection with my statement from the previous post. Another thing to keep in mind is other than Colorado State most other media weather outlets are calling for and active hurricane season, and most of them have the Gulf coast as a target this season.

I think the Gulf is always a target, but I believe "most" of the experts are saying the EC is the likely target this season with the BH being positioned a little farther N and E allowing more recurves and/or NE strikes.

[KWT]

Well I suspect we will get a weak El Nino type feature develop towards the back end of the hurricane season but the key is what state it'll be in during August and September as they are usually the key months for getting strong hurricanes.

[cycloneye]

Australians Mid April Update of ENSO

Details
The SST across the central and eastern tropical Pacific has been warming since February. When averaged over the month of March some cool SST anomalies are still evident across the central and eastern equatorial Pacific. However, steady warming in the last four weeks has seen the weak cool anomalies disappear, with the equatorial Pacific SST currently near normal. The monthly NINO indices for March were –0.4°C, –0.2°C and –0.4°C for NINO3, NINO4 and NINO3.4 respectively.

In terms of weekly data, the most recent NINO indices are +0.3°C, +0.1°C and 0.0°C for NINO3, NINO4 and NINO3.4 respectively. Over the past two weeks all three NINO regions have warmed. NINO3 warmed the most with an increase of approximately 0.4°C, while NINO4 and NINO3.4 warmed by approximately 0.1°C and 0.3°C respectively. The 7-day SST anomaly map map shows that SST across most of the equatorial Pacific is near normal. The weak cool anomalies that had persisted across the tropical Pacific since late 2008 have warmed and dissapeared. When compared with two weeks ago, weak positive anomalies in the far east of the Pacific, near South America, have strengthened slightly. An animation of recent SST changes is available.

The sub-surface of the equatorial Pacific also warmed through March and has continued to warm through the first half of April. However, the sub-surface remains slightly cooler than the long term average in the central and eastern Pacific. This anomalously cool sub-surface water in the central and eastern tropical Pacific has persisted since September 2008. A recent map for the 5 days ending 13 April shows a large area of sub-surface warm anomalies above +1.0°C extending across the western equatorial Pacific. East of 140°W sub-surface water temperature is still generally below average, with weak anomalies below –1.0°C.



Trade winds have generally weakened through March and the first half of April. Over the last three weeks, weak anomalous westerly flow has generally dominated across the central and eastern tropical Pacific. In the last week, anomalous easterly flow has developed in the western Pacific. The latest weekly wind anomalies are shown in the TAO/TRITON map (small image above) for the five days ending 13 April.

The Southern Oscillation Index (SOI) fell sharply through March. The SOI fell from a February value of +15 to value of zero for March. The SOI has increased slightly since the start of April, with a current 30 day value of +5 on the 13 April. The Tahiti mean sea level pressure (MSLP) fell to near normal during March. Previous to March, the Tahiti MSLP had generally been above average since August 2008. The Darwin MSLP, which was below average for much of February also returned to near normal through March. (SOI graph, SOI table).



Cloudiness near the date-line over the central to western Pacific is another important indicator of warm/cool ENSO conditions, as it normally increases/decreases (negative OLR/positive OLR anomalies) during these episodes. Cloudiness near the date-line decreased in December, coinciding with cooling of the sea surface in the region. Cloudiness increased towards the end of February, but still remains below average.

The majority of international dynamic computer models surveyed by the Bureau of Meteorology predict a continuation of neutral conditions for the tropical Pacific until at least mid-winter. Three of the five models are predicting neutral conditions for winter and spring, while two models predict El Niño conditions to develop. The most likely outcome for the period up to mid-winter is for equatorial Pacific SSTs to warm but to remain in the neutral range. Models suggest a return to La Niña conditions is the least likely outcome. Recent forecasts from the POAMA model, run daily at the Bureau of Meteorology, predict ENSO-neutral conditions to persist through to mid-winter, but for El Niño conditions to develop from mid-winter to spring. Pacific conditions and model predictions will continue to be monitored closely for any strengthening indications of an event.

http://www.bom.gov.au/climate/enso/

[wxman57]

Updated forecasts on the NCEP page now forecast an El Nino by July. Previously, they forecast possible El Nino by late September. This would support a lowering of the projected number of named storms. Of course, we have to add in from 2-3 named storms each year that probably shouldn't have been named...

[KWT]

Yep models going into weak El Nino, perhaps a little faster then I had expected but does justify the lower numbers that have been coming out recently from the forecasting agencies.

Of course weak El nino isn't always a killer for seasons, look at 2004 and 1969 for prime examples but it does mean a likely lower season then would otherwise happen.

1951 still looks closest match to this year so far in terms of ENSO.

[jinftl]

If this season has tracks like 1951 it will definitely be an interesting one...some recurves, some long-trackers moving west across the tropics, and florida, the bahamas, and the Outer Banks flirting with/being struck by a few storms

http://upload.wikimedia.org/wikipedia/c ... on_map.png

[cycloneye]

1951 had 8 hurricanes from the 10 named storms that formed that year.

Code: Select all

1 Hurricane ABLE  15-24 MAY  100  -  3   
2 Tropical Storm BAKER  2- 5 AUG  50  -  -   
3 Hurricane CHARLIE  12-23 AUG  115  964  4   
4 Hurricane DOG  27 AUG- 5 SEP  100  -  3   
5 Hurricane EASY  2-13 SEP  140  -  5   
6 Hurricane FOX  2-11 SEP  100  -  3   
7 Tropical Storm GEORGE  20-21 SEP  50  -  -   
8 Hurricane HOW  28 SEP- 8 OCT  95  -  2   
9 Hurricane ITEM  12-17 OCT  70  -  1   
10 Hurricane JIG  15-20 OCT  70  -  1


[tolakram]

1951 had 8 hurricanes from the 10 named storms that formed that year.

Code: Select all

1 Hurricane ABLE  15-24 MAY  100  -  3   
2 Tropical Storm BAKER  2- 5 AUG  50  -  -   
3 Hurricane CHARLIE  12-23 AUG  115  964  4   
4 Hurricane DOG  27 AUG- 5 SEP  100  -  3   
5 Hurricane EASY  2-13 SEP  140  -  5   
6 Hurricane FOX  2-11 SEP  100  -  3   
7 Tropical Storm GEORGE  20-21 SEP  50  -  -   
8 Hurricane HOW  28 SEP- 8 OCT  95  -  2   
9 Hurricane ITEM  12-17 OCT  70  -  1   
10 Hurricane JIG  15-20 OCT  70  -  1


I have to offer the uneducated opinion that those kinds of numbers indicate a much more active season with the smaller storms simply not being noticed / counted.

[HURRICANELONNY]

I hope a strong El Nino comes. A better chance of above normal rain if it happens. As for Nino models. I don't think they are very reliable. It will be a close call. Will it be Neutral or El Nino? Only time will tell.

[cycloneye]

IRI April ENSO Update:



Current Conditions
As of mid-April 2009 SSTs are near-average across much of the equatorial Pacific. During the last couple weeks, colder than average SSTs in the eastern Pacific, indicative of weak La Niña conditions, have been replaced by warmer than average SSTs. The enhanced easterly winds that had been responsible for the cold SST anomalies earlier this year, led to a deepening of the thermocline in the western Pacific and concentration of the warmest waters in the far western Pacific. A relaxation of the easterly winds along the equator allowed warmer water held in the west to begin to move eastward. Although the equatorial Southern Oscillation Index (SOI) remains positive, the traditional SOI has become just slightly negative for the first time since mid-2008. Consistent with deepening of the western Pacific thermocline, the heat content has been slowly increasing since early 2009, and with the ocean adjustment it now appears above average across most of the equatorial Pacific, though it is still very close to average in the central and eastern Pacific.

For March 2009, the SSTs in the NINO3.4 region were more than minimally classifiable as La Niña conditions (-0.55 degrees C anomaly), and for the Jan-Feb-Mar season they were -0.72 degrees C from average. Currently the IRI's definition of El Niño conditions rests on an index of SST anomalies, averaged over the NINO3.4 region (5S-5N; 170W-120W), exceeding the warmest 25%-ile of the historical distribution, and similarly for La Niña relative to the 25%-ile coldest conditions in the historical distribution. The magnitude of NINO3.4 anomaly necessary to qualify as La Niña or El Niño conditions for the Apr-May-Jun and the May-Jun-Jul seasons are approximately 0.45C and 0.50, respectively.


Expected Conditions
The most recent weekly SST anomaly in the NINO3.4 region is -0.1 C, indicating ENSO-neutral conditions in the tropical Pacific. What are the probabilities for maintaining neutral conditions or returning to La Niña conditions? Persistent and large-scale easterly wind anomalies along the equator in the western-to-central Pacific have weakened in the last couple weeks. The thermocline, which contitutes the main element of the tropical Pacific system imparting ENSO predictability, is near its long-time mean depth in the central and eastern part of the Pacific. Deep anomalies in the west are edging eastward, which will make it more difficult to reinstate La Niña conditions. On the other hand, the easterly anomalies have again strengthened in the last week over the western Pacific.

April is within the so-called "predictability barrier" of boreal spring. It is typically easier to predict from this point forward than it was a few months ago and going through the boreal spring. However, the perturbations to the upper ocean structure, which impact predictability to ENSO, are weak at this time. Dynamical models are often more sensitive to these small perturbations than are statistical models that consider the sub-surface ocean, which may be why the dynamical models are all producing notably warmer ENSO forecasts than their statistical counterparts.

Currently, the models indicate probabilities of about 75% for ENSO-neutral conditions, about 25% for the return of La Niña conditions, and very little possbility of developing El Niño conditions for the Apr-May-Jun season in progress. Going forward the models indicate that maintenance of ENSO-neutral conditions is the most likely scenario, with the possibility of developing El Niño conditions more possible than La Niña conditions in mid-2009.


The above assessment was made in part on the basis of an examination of the current forecasts of ENSO prediction models as well as the observed conditions. For purposes of this discussion, El Niño SST conditions are defined as SSTs in the NINO3.4 region being in the warmest 25% of their climatological distribution for the 3-month period in question over the 1950-present timeframe. The corresponding cutoff in terms of degrees C of SST anomaly varies seasonally, being close to 0.40 degrees C in northern late-spring/early-summer season and as high as 0.75 degrees C in late northern autumn. La Niña conditions are defined as NINO3.4 region SSTs being in the coolest 25% of the climatological distribution. Neutral conditions occupy the remaining 50% of the distribution. These definitions were developed such that the most commonly accepted El Niño and La Niña episodes are reproduced.

The models are somewhat split in their ENSO forecasts through the 10-month forecast period, with the statistical models mostly predicting the cool side of ENSO-neutral and the dynamical models predicting warm ENSO-neutral to El Niño conditions. For the current Apr-May-Jun season, about a quarter of the models are predicting La Niña conditions, while almost three-quarters are predicting ENSO-neutral conditions. In fact, throughout 2009, the models favor ENSO-neutral conditions. For the Apr-May-Jun 2009 season, 6 of 22 models (27%) predict La Niña conditions and none predicts El Niño development. At lead times of more than 4 months into the future, statistical and dynamical models that incorporate information about the ocean's observed sub-surface thermal structure generally exhibit higher predictive skill than those that do not. Among models that do use sub-surface temperature information, none indicates the existence of La Niña, 4 of 15 (27%) indicate El Niño conditions for the Aug-Sep-Oct season; 11 of 15 (73%) predict that SSTs will remain ENSO-neutral (Note 1). Caution is advised in interpreting the distribution of model forecasts as the actual probabilities. At longer leads, the skill of the models degrades, and skill uncertainty must be convolved with the uncertainties from initial conditions and differing model physics, leading to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution from that taken verbatim from the raw model predictions.


An alternative way to assess the probabilities of the three possible ENSO conditions is to use the mean of the forecasts of all models, and to construct a standard error function centered on that mean. The standard error would be Gaussian in shape, and would have its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill would result in a relatively narrower error distribution, while low skill would result in an error distribution with width approaching that of the historical observed distribution. This method shows probabilities favoring ENSO-neutral near 75% for Apr-May-Jun and 72% for May-Jun-Jul. ENSO-neutral is favored as being consistently most likely throughout the forecast period. This method also shows that El Niño is more likely than La Niña by mid-2009. The same cautions mentioned above for the distribution of model forecasts apply to this alternative method of inferring probabilities, due to differing model biases and skills. In particular, this approach considers only the mean of the predictions, and not the range across the models, nor the ensemble range within individual models.


The IRI's probabilistic ENSO forecast takes into account the indications of this set of models, the outcome of the standard error approach described above, and additional factors such as the very latest observations that may have developed after the initialization times of some of the models. It indicates a 75% probability for ENSO-neutral conditions in the Apr-May-Jun season in progress, declining to 60% by Jul-Aug-Sep and beyond.

http://iri.columbia.edu/climate/ENSO/cu ... nical.html

A question to any of our pro mets about the models.Which models are the most the people have to look at to see how ENSO will do in the next few months,the statistical models or the dynamical ones?

[HURRICANELONNY]

Thanks for posting that. I never took probabilities and statistics in college. But it does make some sense. As for the dynamical vs. statisical models. That part I have read up on some. I think what it comes down to is AMJ is usually the months to watch.

[wxman57]

IRI April ENSO Update:

http://iri.columbia.edu/climate/ENSO/cu ... _table.gif

That graphic looks like it's from February - the start point of the model runs is in February. Currently, the SST anomaly in Nino 3.4 region is about -.4C, maybe a little warmer, not -.7C as indicated by the blue start point on the graphic. Temperatures are rising steadily in the Tropical Pacific, higher than what a number of the models on the graphic were forecasting. Here's a graphic from the NCEP site which begins in early April. The trend is definitely warmer - to El Nino by July. Of course, April is not a reliable month to predict El Nino/La Nina.

[cycloneye]

Is there an explanation about why the SOI index is moving upwards fast (Now at +7.7 after being at -.4) and the ENSO models continue to forecast warm ENSO?

SOI Data

2009022820090329 -.4
2009030120090330 .8
2009030220090331 .8
2009030320090401 1.1
2009030420090402 1.4
2009030520090403 1.7
2009030620090404 2
2009030720090405 1.8
2009030820090406 2.1
2009030920090407 1.9
2009031020090408 2.8
2009031120090409 3.1
2009031220090410 3.5
2009031320090411 3.9
2009031420090412 4.3
2009031520090413 5.3
2009031620090414 5.1
2009031720090415 5.5
2009031820090416 5.9
2009031920090417 7.7

http://www.bom.gov.au/climate/enso/soi.dt3

[Just Joshing You]

I've been under (the possibly false perception) that a high SOI index means the chance of La Nina is smaller. Is this true?

[KWT]

Very roughly, positive means more of a La Nnia type signal, El Nino suggests a negative signal...but they are just that and sometimes there isnt a very good match between the ENSO state and the SOI.

[cycloneye]

What I know is that a positive SOI is a signal of La Nina and a negative SOI means warm ENSO is a given.I would like to see some experts chimming in here about this recent data of the SOI turning positive again after being negative for a couple of days and what it means if anything about the future forecast of ENSO for the next few months.