posted on 31 August 2015
Written by Sig Silber
For a few days, the 1997/1998 had been showing up as being highly correlated analogs with recent weather conditions. I pay a lot of attention to the analogs as you know if you regularly read my weekly report and this made me wonder if there were signs that this El Nino, which in some sense has arrived, would have impacts that resemble the 1999/1998 El Nino. That would be significant because:
But as of today, the 1997/1998 analogs are not showing up so perhaps we can ignore the run of such analogs the past five days or so as the analogs have been jumping around all over the place. At any rate, we will come back to this topic next week when there will be more time. This week I want to report on the just released NOAA Update for September.
This is the Regular Edition of my weekly Weather and Climate Update Report. Additional information can be found here on Page II of the Global Economic Intersection Weather and Climate Report.
Looking Ahead to Next Week
We will discuss the following four articles. Extra credit will be awarded to those who read them in advance LOL..
El Niño– Generated Weather in the United States Stanley A. Changnon Climatologist, Mahomet, Illinois. You can find the full paper here.
Technical Report 98-02 National Climate Data Center The El Nino Winter of "97-'98". You can find that here.
Both of those focus on impacts.
The two meteorological papers I have been pouring through are:
Genesis and Evolution of the 1997-98 El Nino which can be found here. McPhaden is prolific and I have selected this particular document partly because it is easy to access.
Very strong 1997-98 Pacific warm episode (El Niño) and which can be found here. It is part of a longer NWS Climate Prediction Center analysis which can be found here. I have not read it all and I need to because it deals with the entire world. What I presented perhaps three weeks ago was the evolution chapter of that analysis.
There are other analyses and anything Kevin Trenberth writes about climate is worth reading. But I have tried to keep the reading list on the 1997-1998 El Nino to a minimum. But anyway that is for next week.
This week we will deal only with the NOAA Update of their September Outlook and the usual analysis of the situation that I present each week.
But just to whet your appetite, I have moved a graphic that I have shown for two weeks to the front of the presentation.
As you can see, the 1997 El Nino was not a wet event for CONUS in 1997. It mainly was a wet event for Dec 1997 - Feb 1998. That is why it become important to know what we should be using for guidance.
And now back to the planned discussion for this evening.
NOAA Issues an Update of the September Outlook.
I will provide excerpts from the NOAA discussion now and integrate the maps into the usually discussion of the 6 - 14 Day Outlook.
Basically they are saying their forecast on August 20 was two weeks too early. On September 17 they will issue a new Seasonal Update. I believe the forecasts do not adequately take into account the Atlantic and over-emphasize the El Nino and that is creating some problems. I talk about that more later when I discuss the analogs for today's 6 - 14 Day Outlook.
Now Let us Take a Look at the Current (Right Now to 5 Days Out) Weather Situation:
A more complete version of this report with daily forecasts is available in Part II. This is a summary of that fuller report. This link Worldwide Weather: Current and Three-Month Outlooks: 15 Month Outlooks will take you directly to that set of information but in some Internet Browsers it may just take you to the top of Page II where there is a TABLE OF CONTENTS and you may have to wait for a few seconds for your Browser to redirect to the selected section with that Page or if that process is very slow you can simply click a second time within the TABLE OF CONTENTS to get to that specific part of the webpage.
First, here is a national 12 hour to 60 hour forecast of weather fronts shown as an animation. Beyond 60 hours, the maps are available at the link provided above.
The explanation for the coding used in these maps, i.e. the full legend, can be found here.
The map below is the mid-atmosphere 7-Day chart rather than the surface highs and lows and weather features. In some cases it provides a clearer less confusing picture as it shows only the major pressure gradients. You can see the location of the Four Corners area where Utah, Colorado, Arizona, and New Mexico meet. At this time of the year there is typically a high pressure system near that area and it is called the Four Corners High. When the Four Corners High is centered directly over the Four Corners area, it creates pretty much a block for the Sonoran Monsoon which only visits its northern neighbor when the highs and lows are located in a way that draws the moist air north.
Small changes in the location of that feature make a big difference in the weather of probably about ten or more states.
This High moves around a lot so by the time you view this report, it most likely it will be located somewhere else which results in a different circulation pattern. The current position is most likely to benefit Arizona and perhaps California. If you know where the High is, you can always imagine the clockwise circulation and how that might impact the movement of moisture in from the Gulf of Mexico and up from Mexico and in from the Gulf of California. So this graphic can be very very useful. And it auto-updates, I think every six hours. Even without a weather map, you generally can figure it out. Wind to your back, High to your right, Low to your left.
Because "Thickness Lines" are shown by those green lines on this graphic it is a good place to define "Thickness" and its uses. You can find a full uk.sci.weather style explanation (thorough) at that link or just remember that Thickness measures the virtual temperature (temperature plus moisture content) of the lower atmosphere and is very useful especially in the winter at identifying areas prone to snow and in the summer areas which are going to be hot and humid. Here is a U.S. style explanation of "Thickness" by Jeff Haby who is a valuable source of Haby Hints for anyone who wants an explanation of a meteorological term.
The level of storm activity in the Western Pacific has tapered off quite a bit..
In the Eastern Pacific Tropical Weather Outlook graphic below, notice that there is no Pacific Tropical Storm projected to be close enough to the coast to significantly impact CONUS right now. The Sonoran Monsoon which we commandeered (as well as a large part of what used to be Mexico and is now the U.S. West) and renamed (probably more recently) the North American Monsoon or the Southwest Monsoon is a series of bursts and pauses in activity as it impacts the ten or so states in CONUS with the major impacts being with respect to New Mexico and Arizona.
At this time of the year warm water off of the coast of Mexico, such as from an El Nino, reduces the ocean/land temperature differential and can weaken the Monsoon overall but the cyclones generated by that warm ocean water can enhance the Monsoon for short periods if those cyclones stay close enough to the Mexican coastline.
So that is what is being watched now and I do not see it happening. This graphic is showing the current water vapor with the location of storms forecast out two days so you see what I see. And what I see is a pattern that is keeping Mexico fairly dry. But at least temporarily there is moisture coming up from Mexico and this probably has to do with the positioning of the Four Corners High. It is not a steady stream however and may not fit the definition of a Monsoon although the National Weather Service (NWS) refers to it as Monsoonal Moisture which I think is incorrect. A Monsoon is a seasonal shift in the direction of the prevailing winds. It is caused by the differential in land and ocean temperature as the land heats disproportionately than the ocean in the summer. But with this El Nino and the warm water off the coast of Mexico that differential is less than usual. But yes there are situations where moist air is coming up from Mexico and entering CONUS but it is not 100% accurate to call this Monsoonal Moisture. Sometime this situation is referred to as Pseudo-Monsoonal Moisture and I believe that would be more agreeable to a purist. In a certain sense it does not matter as the precipitation is wet independent of the mechanism involved but in terms of making predictions it is useful to pay attention to the mechanism that are determining the sources of moisture. There is also a tropical depression in the Pacific and there is some thought that this will become a named storm and hug the coast or even come inland. So there are a lot of questions about the short-term picture.
The below graphic is harder to look at but provides more detail on the water vapor being generated by these storms and the normal summer action of the Southwest Monsoon. It covers a much larger area within CONUS so you can see where the moisture currently is and is going. This graphic is very good at pointing out the divisions between cloudy and not cloudy areas. As I am looking at this graphic Monday evening I see a lot of clear sky over the eastern half of CONUS. But one also sees moisture streaming up through Arizona from Mexico. It has not been a steady and heavy stream but as I am looking at it right now it looks like there might be burst of more significant moisture arriving soon. The problem is the situation changes almost moment to moment as it looked very different earlier this afternoon.
Looking at an even larger area, below is a view which highlights the surface highs and the lows re air pressure on Day 6 (Day 3 can be seen in Part II of this Report). The Eastern Pacific Subtropical High is no longer serving as a total block to all storms attempting to move from the Pacific into CONUS and is now located further offshore. Notice the Low just southwest of that High. It might be the first sign of the El Nlno but it has not strengthened. Overall they has not been much change for weeks.
We now need to monitor the Jet Stream to see if it is shifting to the South.
This is the forecast out five days. The activity still appears to be north rather than south. So the El Nino has not yet really impacted the weather situation for CONUS.
Outlook Days 6 - 14 (but only showing the 8 - 14 Day Maps)
Here is the prior temperature outlook issued on August 20 which was updated today.
Here is the updated September Temperature Outlook issued today. It shows a much warmer Eastern CONUS but remember this is an amalgam of two half months which are projected to be quite different from each other.
Here is the current 8 - 14 Day Temperature Outlook which will auto-update and thus be current when you view it. It covers the week following the current week. Today's 6 - 14 Day Outlook is just nine days of the month and the map shown below of the 8 to 14 day Outlook only shows seven days. The 6 - 10 Day Map is available on Page II of this report. As I view this map on August 31 (it updates each day) it appears that the map reflects the perspective that El Nino will not be a factor in the first half of September.
Here is the prior September Precipitation Outlook issued on August 20, 2015 which was updated today.
And here is the updated September Precipitation Outlook issued today. Remember it represents an amalgam of two half months both of which are projected to be significantly different. It clearly shows a wetter northern tier in the central part of CONUS which is not consistent with an El Nino.
Below is the current 8 - 14 Day Precipitation Outlook which will auto-update daily and thus be current when you view it. And again remember that this map shows only seven days and the 6 - 14 Day map is available on Page II of this report. As I view this map on August 31 (it updates each day), the pattern is very wet.
Here are excerpts from the NOAA discussion released today August 31, 2015.
Analogs to Current Conditions
Now let us take a detailed look at the "Analogs" which NOAA provides related to the 5 day period centered on 3 days ago and the 7 day period centered on 4 days ago. "Analog" means that the weather pattern then resembles the recent weather pattern and was used in some way to predict the 6 - 14 day Outlook.
Here are today's analogs in chronological order although this information is also available with the analog dates listed by the level of correlation. I find the chronological order easier for me to work with. There is a second set of analogs associated with the outlook but I have not been analyzing this second set of information. This first set applies to the 5 and 7 day observed pattern prior to today. The second set which I am not using relates to the forecast outlook 6 - 10 days out to similar patterns that have occurred in the past during the dates covered by the 6 - 10 Day Outlook. That may also be useful information but they put this set of analogs in the discussion with the other set available by a link so I am assuming that this set of analogs is the most meaningful.
Again the analogs do not suggest that this El Nino will impact our weather over the next two weeks. The 1969 El Nino is interesting as it immediately followed an El Nino Modoki Type II. This El Nino followed a warm event which if a bit stronger would have been an El Nino Modoki Type II. This El Nino is much stronger than the 1969 El Nino but it may be giving some clues as to what to expect. As with last week, there is a slight suggestion of McCabe Conditions A and D. They are pretty much the opposites of each other confirming the confusion of the current situation re making forecasts. The seminal work on the impact of the PDO and AMO on U.S. climate can be found here.
You may have to squint but the drought probabilities are shown on the map and also indicated by the color coding with shades of red indicating higher than 25% of the years are drought years (25% or less of average precipitation for that area) and shades of blue indicating less than 25% of the years are drought years. Thus drought is defined as the condition that occurs 25% of the time and this ties in nicely with each of the four pairs of two phases of the AMO and PDO.
Historical Anomaly Analysis
When I see the same dates showing up often I find it interesting to consult this list.
With respect to relating analog dates to ENSO Events, the following table might be useful. In most cases this table will allow the reader to draw appropriate conclusions from NOAA supplied analogs. If the analogs are not associated with an El Nino or La Nina they probably are not significant. Remember, an analog is indicating a similarity to a weather pattern in the past. So if the analogs are not associated with a prior El Nino or prior La Nina the computer models are not likely to generate a forecast that is consistent with an El Nino or a La Nina.
Progress of the Warm Event
Let us start with the SOI.
Below is the Southern Oscillation Index (SOI) reported by Queensland, Australia. The first column is the tentative daily reading, the second is the 30 day moving/running average and the third is the 90 day moving/rolling average.
This past week has continued to be consistent with the presence of the current El Nino. The 30-day average, which is the most widely used measure, on August 31 was reported as being -18.91 which is clearly a reading associated with a strong El Nino. The 90-day average also is solidly in El Nino territory at -14.98. The SOI is clearly indicative of an El Nino Event in progress.
Here are the low-level wind anomalies. It has been fairly calm although there is some activity between 160W and 140W.
In this graphic, you can see how the convection pattern (really cloud tops has since May shifted to the East from a Date Line (180) Modoki pattern to a 170W to 120W Traditional/Canonical El Nino Pattern. But recently the signs of an El Nino are getting quite faint and shifting back to the west. You can see the lack of convection over at 120E which is Indonesia but the convection has withdrawn to the West not moved to the East as would be the case with a normal El Nino. That may still happen. In the 1997/1998 El Nino, that did not happen until 1998 which is why the Fall and Winter of 1997 were not wet for CONUS. When I hear that with this El Nino the atmosphere is strongly coupled with the ocean, I really wonder what those meteorological agencies are smoking. It might be true on a worldwide basis but it does not appear to be the case as it impacts CONUS.
Let us now take a look at the progress of the Kevin wave which is the key to the situation. Since February there have been three successive downwelling Kelvin Waves without really an upwelling Kelvin Wave on any consequence to counter their impact. The first wave which started in February was the most effective at getting this El Nino started. The second wave reinforced to some extent but not much and this third (and I believe last) downwelling Kelvin Wave has created an El Nino that will have a major peak coming soon and an extended life but at a diminished strength.
The main impact of this latest Kelvin Wave has already moved east to 170W where it is not ready to exist stage right just yet but it will within two or three months. You can see where some of the warmer water has moved to the east a bit to 155W. You also see the intense activity between 140W and 120W which is in the area where the ONI is measured. You also see the cooling down of the water east of 90W which may signify the end stage of this El Nino. It is a slow process and every El Nino has a different length. But if you think of an El Nino as typically lasting about a year or less, then this one is about half through its life.
We are now going to change the way we look at a three dimensional view of the Equator and move from the surface view to the view from the surface down. When I examine the current situation as compared to the 1997/1998 El Nino which I described graphically last week, the current El Nino has developed more rapidly. This El Nino is a couple of months further along in its evolution than the 1997/1998 El Nino and will end earlier in the winter than the 1997/1998 El Nino. Also the 1997/1998 had a larger amount of slightly warmer subsurface water in the Eastern Pacific and that water takes time to surface, create convection, and thus cool. Something happens to allow the Easterlies to resume their strength and that in turn moves this water back towards the Western Pacific Warm Pool.
Current Sub-Surface Conditions
Top Graphic (Anomalies)
The above graphic showing the current situation has an upper and lower graphic. The bottom graphic shows the absolute values, the upper graphic shows anomalies compared to what one might expect at this time of the year in the various areas both 150W to 90W Longitude and from the surface down to 450 meters.
The top graphic is the most useful of the two and shows where 2C (anomaly) water is impacting the area in which the ONI is measured i.e. 170W to 120W. The 2C anomaly now extends to 160W which is very impressive. There is also a small blip over at 175W. The subsurface warm water appears to be making its way to the surface in the Eastern Pacific. The 3C anomaly is over towards 140W which again is very impressive.
One big issue is where will the +6C and +5C anomaly water go as it reaches the beaches of Ecuador? To the extent it surfaces, it can create convection and impact the Walker Circulation which could then provide positive feedback to this El Nino. But that warm water might tend to go north or south or both. That is part of the phase out process for an El Nino and that is where we are in the life of this El Nino. It is peaking and will soon begin its decline. But it is certainly taking its sweet time probably because of the large amount of the subsurface warm water. Water is a very good insulator: I believe it has the second highest specific heat capacity of all known substances.
So that means that other than by mixing, that warm water under the surface will stay warm until it rises to the surface where it can be cooled by evaporation (while making clouds) or moves to the north where it will impact Mexico and the Southern Coast of the U.S. That is part of the basis for models predicting that the ONI of this El Nino will continue to rise.
Bottom Graphic (Absolute Values which highlights the Thermocline)
The bottom half of the graphic is not that useful in terms of tracking the progress of this Warm Event as it simply shows the thermocline between warm and cool water which pretty much looks like this as shown here during a Warm Event and you can see that the cooler water is not yet fully making it to the surface to the east along the coast of Ecuador. However, one now can see the increase in the slope of the thermocline (look at the 25C dividing line for example which has now reached the surface). We can now begin to monitor the 20C Isotherm which is often thought of as being the middle or lower edge of the thermocline where the slope is also steepening and looks like it may reach the surface fairly soon. I said that last week and a week has gone by with essentially no change.
"Taking a close look at the bottom half of the TAO/TRITON graphic, notice that the 1.5C+ anomaly in the western part of the Nino 3.4 Measurement Area north of the Equator had almost vanished.last week but has since then strengthened to some extent. You can see a small area of 2.5C to 3C surface water and a much larger area of 2C to 2.5C water which combined might be considered to be an area of 2.5C water which if it extended throughout the Nino 3.4 measurement area would result in an ONI of 2.5C which if it lasted for three months would make this the most powerful El Nino ever in modern times. But in half of the Nino 3.4 measurement area, you have an ONI of perhaps 1.2 or slightly higher which is pretty much a run of the mill El Nino.
So this raises real questions about how we measure an El Nino and how we do regression analysis on historical El Ninos. Are the likely impacts to be correlated with a 1.0 ONI which has minimal impact or a 2.5 ONI which is off the charts? I guess we will find out. The distribution of SST anomalies has changed dramatically over the last three weeks.
For my own amusement, I calculate the ONI each week using a method that I have devised. To refine my calculation, I have divided the 170W to 120W ONI measuring area into five subregions (that I have designated A through E (from west to east) with a location bar shown under the TAO/TRITON Graphic) and have mentally integrated what I see below and recorded that in the table I have constructed. Then I take the average of the anomalies I estimated for each of the five subregions.
So as of Monday August 31 in the afternoon working from the August 30 TAO/TRITON report, this is what I calculated which is basically the same as my calculation last week although the patterns of the anomalies have been changing around quite a bit but the changes have been cancelling each other out.
My estimate of the Nino 3.4 ONI has increased slightly to 1.7. NOAA has today reported the weekly ONI as being 2.2 a slight increase from what was reported last week and certainly a very high level for an ONI even though it is a weekly value not a three month average. I can not replicate the value reported by NOAA which has me concerned. The increase in the NOAA estimated ONI is I believe mostly due to the subsurface water in the Eastern Pacific backing up to the west as it comes to the surface. This warm water certainly impacts the weather in Ecuador and Peru but may not have a direct impact on weather in CONUS other than by spawning tropical cyclones which move north and enter the circulation of the Southwest Monsoon. That activity seemed to have decreased recently but it looks like we are getting another spurt of it.
Nino 4.0 is now reported as being 1.1. You can already see (in my calculation table) the gradient from West to East that has formed with the higher values in the East and the Western part of the Zone having a smaller anomaly which I believe has already begun to decline.
The real action is in Nino 1+2 which is now reported as being back up to 2.0. The issue remains the extent to which warm water off of Ecuador and Peru impacts CONUS weather. I think it has very little impact and that is what we are seeing right now.
Here is another way of looking at it: Unlike the Upper Ocean Heat Anomaly Hovmoeller which takes an average down to 300 meters this just measures the surface temperature anomaly. It is the surface that interacts with the atmosphere. As you can see the warm water rising off the South American Coast has worked its way all the way over to beyond 170W so it fully contributes to the increasing ONI. But at the same time one can now clearly see that the water immediately off the coast of South American is generally cooling down. It is a dynamic process and this El Nino is both continuing to grow while beginning to wane. I think the waning is accelerating. But there remains a lot of subsurface warm water to be disposed of. That is a slow process
and will continue for some time.
El Nino in the News
I did not find anything particularly useful to report this week.
Recent Impacts of Weather Mostly El Nino but possibly Also PDO and AMO Impacts.
I was not satisfied showing a 90 day and a 30 picture since the 30 day is subsumed into the 90 day so I decided to show three one-month pictures as I think that is a lot easier to follow. I do not plan to update the prior two months each week but monthly.
First the Temperature and Precipitation Departures from two months ago
Then the same graphic one month later
And then what was the current 30-Day picture one week ago. So this gives us a three-month sequence of monthly departures.
That series of graphics showed a drying trend which is not exactly what you would expect with an El Nino arriving. For many parts of CONUS, it was a cooling trend also which may be associated with an El Nino.
And now the view from August 29 which is one week short of a month later.
One can see the continued drying out but some easing of the drying in Mexico. There has also been a shift in the temperature regime. The El Nino ate the Monsoon that is for sure.That does not mean there can not be Monsoonal Bursts but that they are now likely to be less frequent and weaker than on average for this time of the year.
On an average basis September is the time when the Monsoon slows down but is still a factor.
View from Australia
Here is the just released discussion:
IOD (Indian Ocean Dipole)
It comes with only a very short discussion and here it is
To me it is interesting that the IOD appears to have peaked and is on the way down. But the interrelationship between the IOD and El Nino is complicated and not fully understood.
Putting it all Together.
We are in El Nino conditions now. The actually impacts on CONUS are not clear. We started by having wetter conditions than usual in the Southwest but that has tapered off quite a bit. It is probably influencing the IOD to tend towards being positive thus providing a double whammy for parts of Asia and Australia. The length and intensity of this El Nino is still not clear mostly in terms of whether or not it will extend into the early part of 2016. All the computer models predict that it will last longer than my mental model suggests to me. The disagreement is in terms of a couple of months but a couple of months makes a difference in terms of agriculture and other economic impacts. We may or may not have a Pacific Climate Shift as the PDO+ may be simply related to the Warm Event (and quite frankly at this point appears to be). But for now we do have PDO+. The AMO being an overturning may be more predictable so the Neutral status moving towards AMO- is probably fairly reliable but not necessarily proceeding in a straight line. So none of this is very difficult to figure out actually if you are looking at say a five-year forecast. The research on Ocean Cycles is fairly conclusive and widely available to those who seek it out. I have provided a lot of information on this in prior weeks and all of that information is preserved in Part II of my report in the Section on Low Frequency Cycles 3. Low Frequency Cycles such as PDO, AMO, IOBD, EATS. It includes decade by decade predictions through 2050. Predicting a particular year is far harder.
We are beginning to speculate on the winter of 2016/201 which I believe will tend to be ENSO Neutral but I am not so sure that it will not lean towards being a cool event or at least closer to a La Nina than neutral. One thing is fairly certain for the U.S. it will be less wet and warmer than the winter of 2015/2016 which will be quite wet and cool. JAMSTEC is predicting that the Spring of 2017 will begin a mild La Nina.
TABLE OF CONTENTS FOR PART II OF THIS REPORT The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page II where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.
A. Worldwide Weather: Current and Three-Month Outlooks: 15 Month Outlooks (Usefully bookmarked as it provides automatically updated current weather conditions and forecasts at all times. It does not replace local forecasts but does provide U.S. national and regional forecasts and, with less detail, international forecasts)
1. Very High Frequency (short-term) Cycles PNA, AO,NAO (but the AO and NAO may also have a low frequency component.)
D. Reserved for a Future Topic (Possibly Predictable Economic Impacts)
TABLE OF CONTENTS FOR PART III OF THIS REPORT - GLOBAL WARMING WHICH SOME CALL CLIMATE CHANGE. The links below may take you directly to the set of information that you have selected but in some Internet Browsers it may first take you to the top of Page III where there is a TABLE OF CONTENTS and take a few extra seconds to get you to the specific section selected. If you do not feel like waiting, you can click a second time within the TABLE OF CONTENTS to get to the specific part of the webpage that interests you.
D2. Climate Impacts of Global Warming
D3. Economic Impacts of Global Warming
D4. Reports from Around the World on Impacts of Global Warming.
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