Guest post by: Dr. Philip Klotzbach, Research Scientist, Department of Atmospheric Science, Colorado State University
As an author on the Colorado State University (CSU) seasonal hurricane forecast, I read with interest the blog regarding “Global Tropical Cyclone Activity still at 30 year low” posted yesterday. I have started to receive questions from the media asking where the hurricanes in the Atlantic are. We forecast a very active season, calling for a total of 18 named storms, 10 hurricanes and 5 major hurricanes (compared with the climatological average of 11 named storms, 6 hurricanes and 2 major hurricanes). Before I go into more detail describing why I think it is too early to think that this is a seasonal forecast bust, I wanted to briefly address the global storm component.
I completely agree that tropical cyclone (TC) activity is very quiet so far for this year’s Northern Hemisphere season. The Northeast Pacific had no named storms during the month of July, which is the first time that this has happened since 1966. The Joint Typhoon Warning Center did not name its fifth storm in the Northwest Pacific until August 8, which is also a record. The North Atlantic has also been very quiet since Hurricane Alex in late June. Alex was the strongest storm in terms of wind speed in the month of June in the North Atlantic since Alma (1966).
With a moderate La Niña event, it is typical to expect reduced activity in the Northwest Pacific and the Northeast Pacific. It has been well-documented that storm formations in the Northwest Pacific shift northwestward in La Niña years (Camargo et al. 2007). Consequently, these storms have less time to track over warm ocean water before making landfall and therefore have less time to reach their maximum potential intensity.
Northeast Pacific storm activity is also typically reduced in La Niña years, due to anomalous upper-level easterly winds that develop at upper levels associated with the strengthening and westward-shifting of the Walker Circulation (Figure 1). From a climatological point of view, upper-level winds in the Northeast Pacific blow out of the east (Figure 2), so stronger upper-level easterly winds increases vertical wind shear, which is detrimental for storm formation. Upper-level winds in the North Atlantic’s Main Development Region (MDR) (defined as 10-20°N, 20-70°W) blow out of the west in a climatological average (Figure 3), so anomalous upper-level easterlies reduces vertical wind shear (Wang and Lee 2009).
Figure 1: Correlation between the August-October Nino 3.4 index and 200 mb zonal winds. These correlations imply that a La Niña event increases vertical shear in the Northeast Pacific while reducing vertical shear in the North Atlantic.
Figure 2: Climatological upper-level winds in the Northeast Pacific during the months of August-October. Note that the climatological upper-level winds are easterly (so upper-level easterly anomalies associated with La Niña increases vertical wind shear).
Figure 3: Climatological upper-level winds in the MDR of the North Atlantic during the months of August-October. Note that the climatological upper-level winds throughout most of the MDR are westerly (so upper-level easterly anomalies associated with La Niña reduce vertical wind shear).
I want to begin addressing the North Atlantic component of the TC activity by examining historical hurricane seasons in La Niña years. I selected years that had an August-October averaged Nino 3.4 index less than -0.5°C since 1950. I calculated August-October averages from the Climate Prediction Center’s dataset available here:
http://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices
I thought that an easy way to examine the typical progression of these seasons was to see when the 2nd hurricane formed. So far in 2010, the North Atlantic has had only one hurricane (Alex). Table 1 displays the La Niña years since 1950 along with the date of 2nd hurricane formation and the seasonal Accumulated Cyclone Energy (ACE) index for that year. ACE is defined as the sum of the square of a named storm’s maximum wind speed (in 104 knots2) divided by 10000. The 1950-2000 average of this index was 96, and for the 2010 season, we are predicting a value of 185.
Table 1: La Niña years since 1950 along with the date of 2nd hurricane formation and the seasonal ACE accumulated in each year.
| Year | ASO Nino 3.4 | 2nd Hurricane Formation Date | Seasonal ACE |
| 1995 | -0.66 | 8/1 | 227 |
| 1970 | -1.04 | 8/2 | 40 |
| 1956 | -0.63 | 8/10 | 54 |
| 1955 | -1.39 | 8/12 | 199 |
| 1971 | -0.63 | 8/15 | 97 |
| 1973 | -1.20 | 8/20 | 48 |
| 1950 | -0.75 | 8/20 | 243 |
| 1999 | -1.01 | 8/22 | 177 |
| 1998 | -1.17 | 8/25 | 182 |
| 1954 | -0.98 | 8/27 | 113 |
| 1975 | -1.34 | 8/30 | 76 |
| 1974 | -0.53 | 8/31 | 68 |
| 2007 | -0.92 | 9/2 | 74 |
| 1964 | -0.86 | 9/3 | 170 |
| 1961 | -0.52 | 9/3 | 205 |
| 1988 | -1.55 | 9/9 | 103 |
The average date of 2nd hurricane formation for all of these years is August 21, and you will note that five years with very high ACE values of 170 or greater did not have their 2nd hurricane formation until August 20th or later. The 2nd storm in 1961 did not form until September, and that September went on to have four major hurricanes, a record for the month. So, from a climatological perspective, it is not time to write off the TC season yet.
With regards to sea surface temperature (SST) anomalies, they are still running at record levels across the MDR, based on data from the NCEP/NCAR Reanalysis. I calculated the July SST over the MDR and have plotted the timeseries from 1948-2010 below (Figure 4). July 2010’s value was at record levels, approximately 0.1°C greater than it was in 2005. Calculations were made from the following website:
http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
Figure 4: July SST averaged over the MDR. The value of 27.5°C reached in 2010 is the warmest on record, beating out 2005 and 1958 by approximately 0.1°C.
I tend to disagree with the SST analysis given by Steve Goddard yesterday. Other SST datasets that I look at in real-time tend to agree with the fact that the MDR is running at record or near-record levels right now. Here’s an additional analysis from NOAA (Figure 5):
Figure 5: Real-time SST anomaly analysis from NOAA.
In addition, analysis from the Advanced Very High Resolution Radiometer of the difference in SST between 2010 and 2005 indicates comparable SSTs throughout the MDR (Figure 6).
Figure 6: SST difference between 2010 and 2005. Note that there are only small differences between the two years.
The sea level pressure anomaly and low-level wind pattern in July would also tend to reinforce the very warm SST anomalies that were already in place from the spring. Figure 7 displays the SLP anomaly pattern in July, while Figure 8 displays the 925-mb wind anomalies. The trades were very weak in July, which is to be expected from the pressure gradient pattern observed in Figure 7. Very weak trades were observed over the MDR, which feeds back into continued warmth due to reductions in mixing and upwelling.
Figure 7: Anomalous sea level pressure in July. This pressure gradient pattern drives anomalous low-level westerly flow, thereby weakening the trades across most of the MDR.
Figure 8: Anomalous 925-mb winds in July. Note the anomalous westerly flow across most of the MDR, implying weaker trade winds (which feed back into warmer SSTs).
With that being said, it does appear that TC activity in the Atlantic should increase over the next couple of weeks. There are a couple of systems that currently have a high chance of formation into TCs in the next 48 hours according to the National Hurricane Center’s website. In addition, we should be heading into a more favorable large-scale regime for TC formation according to the latest Madden-Julian Oscillation forecasts. I showed in a paper published earlier this year that when the MJO is located in Phases 1 and 2 (convectively active over the Indian Ocean), it reduces vertical wind shear in the tropical Atlantic, thereby providing a more conducive environment for formation on a shorter time-scale basis (Klotzbach 2010). The GFS ensemble is hinting that the MJO may be amplifying in the Indian Ocean in the next couple of weeks (Figure 9).
Figure 9: Ensemble GFS forecast for the MJO over the next two weeks.
To summarize, I would say that it is too early to discount seasonal forecasts issued by CSU, NOAA and other agencies. Our August forecast has shown significant skill over the period from 1984-2009, with our average real-time forecast error over that time period being ± 2.2 named storms, ± 1.7 hurricanes and ± 1.1 major hurricanes. Correlations between our early August predictions and post-31 July TC activity are approximately 0.60 for most predictands over that same period. Full forecast verifications from CSU are available here:
http://tropical.atmos.colostate.edu/
NOAA’s forecasts show similar levels of skill. While seasonal forecasts do bust on occasion, these forecasts show moderate skill in real-time and should not be dismissed this early in the TC season.
References:
Camargo, S. J., A. W. Robertson, S. J. Gaffney, P. Smyth, and M. Ghil, 2007: Cluster analysis of typhoon tracks. Part II: Large-scale circulation and ENSO. J. Climate, 20, 3654-3676.
Klotzbach, P. J., 2010: On the Madden-Julian oscillation-Atlantic hurricane relationship. J. Climate, 23, 282-293.
Wang, C. and S.-K. Lee, 2009: Co-variability of tropical cyclones in the North Atlantic and the Eastern North Pacific. J. Geophys. Res., 36, L24702,doi:10.1029/2009GL041469.
Dr K very interesting and informative on forecasting methodology. Most on this site don’t take issue with the very brave activity of Trp Stm forecasting per se but rather in blaming frequency on gw. You graciously did not do that found a respectful and thankful readership.
Dr K,
With all due respect, these things sound reasonable, and they sound as if they should matter, but do they in fact allow you to predict what you claim? Why have you been unable to predict the historic low ACE? Why have so many recent storms failed to live up to these predictions? Even if you nail this year (which I doubt based on 38 years of living in the gulf coast), you will have to hit the nail repeatedly in good times and bad to have a valid claim that you hold this elusive key.
I second the call for where are the predictions of low years. The constant call for historic high numbers is something of a joke here at sea level.
Gerry
I TOLD YOU THERE WOULD BE ZERO HURRICANES JUST LIKE LAST YEAR. WHY DON’T THEY LISTEN TO ME?
“Our August forecast has shown significant skill over the period from 1984-2009, with our average real-time forecast error over that time period being ± 2.2 named storms, ± 1.7 hurricanes and ± 1.1 major hurricanes.”
So if I said 9 named storms, 3 hurricanes and 2 major hurricanes I’d be right with 7-11 named storms, 1-5 hurricanes and 1-3 major hurricanes. That’s quite a range doc, 150% for named storms, 500% for hurricanes and 300% for major hurricanes.
I rest my case.
Is there any good evidence that all this statistical effort produces better predictions than looking at chicken’s entrails or asking the Oracle at Delphi?
Dr. Klotzbach,
I’d like to personally thank you for posting your thoughts here. I may have a different train of thought than most posters here. Personally, I’ve always recognized that some years have more hurricanes than others. I live in Kansas, so the hurricanes rarely effect me, but when they do, it is in the forms of tornadoes. I give little thought to either. They come, they go. Sometimes with more frequency than others, still, they come, they go.
My question and my observation is, are you aware of the focus of hurricanes in regards to the climate change question? And, are you aware of your influence on the question of hurricanes? I’m not implying you should or shouldn’t change the way you forecast. That would be silly. Still, by your forecasts, regardless of the accuracy(I believe you’re more correct than wrong), some have told me that(your prognostications) are “proof” positive of climate change due to CAGW. I’m just wondering if you are aware of your influence in the discussion and how you deal with it. Please note, I’m not asking for your emotional response. I don’t care if you chant to your ancestors or do like I do (drink heavily), I’m wondering if you regard your statements as having impact on the CAGW discussion.
I thank you for any response.
James Sexton
Something similar from JB:
http://www.accuweather.com/video/424570870001/no-changes-to-my-hurricane-idea.asp?channel=vbbastaj
Re: TomRude
Walker circulation does play a role. Makarieva et al. say that hurricanes develop when there is much vapor in the atmosphere.
When trade winds are weak, the income of moisture to the region of hurricane formation is slow. Whether temperatures are high or low at the equator, without intense vapor import hurricanes will not form actively — they would have no food!
So weak trades and reduced hurricane activity do seem to me to agree with what Makarieva et al. would predict (little vapor –> few hurricanes). On the contrary, I see little agreement between the conventional paradigm (high temp –> many hurricanes) and what actually happens.
Really, some physical considerations rather than pure statistics would be welcome.
Mike Jonas says:
August 10, 2010 at 6:20 pm
I believe that graphic came from CSU and Bill Gray, and is in the latest Klotzbach/Gray forecast at http://hurricane.atmos.colostate.edu/Forecasts/2010/aug2010/aug2010.pdf . Yep. Page 39, except the image there is updated to the recent THC data – 1980-1994 and 1995-2009.
Thank you Dr. Klotzbach, a very interesting read. Predicting chaotic events takes more guts than I have. It is like predicting the outcomes of team sports with well matched opponents, not easy to do. My hope is you are on the high side. My logical alter ego tells me you are probably in the ballpark. My scouting experience tells me prepare for the worst and hope like hell for the best.
Has Dr Hansimian passed any comment yet?
The Russians spent almost seventy years having to lie to survive–the scientific community had to lie and denounce the people they esteemed or go to camps. Now they don’t have to. When the nuclear winter fraud was being advanced by American scientists to “save the world from Ronald Ray-gun,” they laughed at it. This decade they told Putin it was a hoax (he signed the Kyoto Protocol for financial reasons.) Their big worry is global cooling.
I always prefer the blindfold and pin approach to weather forecasting.
Thanks for this post – much appreciated – but to follow up a question on the impact of some statements on the very public debate – especially in the lead up to Cancun and also the activity in parliaments and senates around the world – the new ‘record’ temperatures are very marginally above 1950, there being two obvious peaks and a trough in-between – and I doubt that the second peak is statistically significant in its ‘record’ above the first peak. The media will run with the ‘record’ from the official spokesmen who ought to know, etc.
The real question for science is – what causes the peaks? Is there a cycle? What are the mechanisms that drive the cycle. And the question for policy is – why don’t people at NCAR/UCAR/NOAA – and you can add Hadley here in the UK, talk about cycles?
These peaks and troughs coincide with both the Arctic Oscillation and the Pacific Decadal Oscillation – what do the oceanographers have to say? And what does the palaeo-record show about frequency and any longer term patterns?
And a question about the oil slick – if you can help – there is a lot of speculation on the wilder blogs about the ‘Loop Current’ in the Gulf shutting down and affecting the North Atlantic Gulf Stream. It seems unlikely, but do you have any information on this? Could the very low ACE levels have caused the Loop Current to fade (I assume it is driven by wind patterns), and would this feed back to the Atlantic current system – or rather, would they be subject to a common cause?
Well, if the “18 named storms, 10 hurricanes and 5 major hurricanes” do occur this year it will no doubt be blamed on AGW in the same way as Louise Gray is now quoting other well known “Alamists” for blaming Russian heat and Pakistani downpours on AGW here:
http://www.telegraph.co.uk/news/worldnews/asia/pakistan/7937269/Pakistan-floods-Climate-change-experts-say-global-warming-could-be-the-cause.html
I thought there had been similar events in the past, but maybe I am wrong. No doubt Pamela Gray have some comments on the behaviour of the Jetstream. Is it unusual and caused by AGW or just weather?
@Dale Rainwater. Klotzbach
How’s about you apply tropical storm theory to make a year-by-year 30-year prediction?
Just kidding. There’s no such thing as tropical storm theory. There is statistical analysis of the past and predictions made based upon it. In other words it’s actuarial science and can only properly be called science if we conflate math and science. A less flattering but more commonly understood characterization for weather and climate predictions would be to call them educated guesses.
So let’s look at the possible variability:
1973 had an intense La Nina (-1.20), its second named hurricane on 20 August, and very weak ACE index of 48.
1950 had a modest La Nina (-0.75), its second named hurricane on 20 August, and very strong ACE index of 243.
Here’s my educated guess for 2010 ACE. The average of 1950 and 1973 is 148 but due to the recent multi-year lull I’m going to move it closer to 1973 by adding in the average of all years (48+96+243)/3 or a 2010 ACE of 129.
I’ll give you even money that my guess is closer than yours.
Dr. Klotzbach,
First, thanks for coming here and providing this information. Hopefully, you won’t receive the same treatment Dr. Curry has received.
I do have a problem. When the predictions based on a hypothesis fail, it’s time to reexamine the basics. Is the data set correct? Has it been interpreted and analyzed properly? Have the phenomena been modeled or simulated accurately? Has a key process or factor been omitted?
You know this. Why hasn’t it been done? Or, if it has, why haven’t we seen the result of the reexamination?
As Frank K. points out above, “We will need to average at least one storm per week, and nearly one hurricane per week and one major hurricane every 2.5 weeks” in order to match your prediction.
My field is system analysis and engineering, but some of my experience has been obtained in pure research programs. Based on that experience, I can tell you the first problem you need to address (i.e. reexamine the basics): Your SST data is flawed.
Based on nothing more than the current 30-year record lull it’s a pretty safe bet to say the only direction it will go from here is up. I’ll step out on an even longer limb and predict that after it increases to the next 30-year record high we can expect it to go down.
Good post. Data and analysis, that’s all that’s required.
First, at the time of this comment it seems that TD-5 has petered out before becoming a tropical storm.
Secondly, hurricane predictions are almost always high. The bureaucracy doesn’t want to have people come back and claim they weren’t prepared because NOAA said it would be a weak hurricane season. I’m skeptical of this comment:
>> Our August forecast has shown significant skill over the period from 1984-2009, with our average real-time forecast error over that time period being ± 2.2 named storms, ± 1.7 hurricanes and ± 1.1 major hurricanes. <<
I wonder just how many of the forcast errors were too low. I doubt there were many years where that was the case, and suspect a plot of the error vs. frequency would not be centered on zero.
I hope everyone here realizes that the hurricane season is from June 1st to November 30th. So even though the most active part of the season if from August to October, this doesn’t rule out the possibility of a named storm or two in November. So this 12 or 13 week deal with one storm per week doesn’t necessarily have to happen to accomplish the 18 named storm forecast.
Thanks for all of the comments. I’ll try to answer some of the questions here:
With regards to hurricanes and AGW, an extensive discussion is located in our latest forecast on pages 38-49 here: http://tropical.atmos.colostate.edu/Forecasts/2010/aug2010/aug2010.pdf
I have also published a paper that looked at trends from 1986-2005 in Geophysical Research Letters:
http://tropical.atmos.colostate.edu/Includes/Documents/Publications/klotzbach2006.pdf
With regards to our skill, a correlation of 0.60 implies that we can explain about 35% of the variability. Obviously, there is significant room for improvement here, but honestly, I would suspect that due to the inherent uncertainty in the climate system, only 50-60% of the variance is predictable. When I build a statistical model in hindcast mode using 3 or 4 predictions (e.g., using the past to predict the future), I typically achieve this level of variance explained. Obviously, there will be slight degradation when applying the forecast model in real time, which is why I attempt to build the dataset over a certain period, say 1948-1989 and then test the equations over an additional period 1990-2009. Having solid physical links between a predictor and hurricanes is also very important. I’d suggest that the interested reader look at our forecasts. There is a lot more than just numbers… a forecast typically runs 50-60 pages and discusses in detail the various models that we utilize to come up with our forecast numbers.
I’m aware that the reliability of the data degrades as we go back further in time. However, we have to deal with the data we’re given. Am I positive that the MDR temperatures are exactly 0.1C warmer than they were in 2005? No, but given the wide variety of analysis techniques that we currently have, we can say with certainty that it’s very warm out there.
We have redesigned our statistical models over time as more datasets have come online. When Dr. Gray started issuing seasonal forecasts in 1984, we only had about 30 years of reliable data. We now have the NCEP/NCAR Reanalysis which is, in my experience, about the most reliable dataset that we have for fields such as SLP, SST and zonal and meridional wind. These fields typically have better reliability than some other fields in the reanalysis, since they are mostly driven by observations. This dataset runs from 1948-present and is being updated in near real-time. Some surface datasets go back to 1900-1947, which although having less reliability, allow for some additional model testing.
I’ve also published a paper in GRL looking at the skill of our forecasts over the period from 1984-2008:
http://tropical.atmos.colostate.edu/Includes/Documents/Publications/klotzgray2009.pdf
Thanks again for all of the comments!
John W. says:
August 11, 2010 at 5:09 am
Don’t worry about Dr. Curry – she knew the fight pit she was heading into. Don’t worry about Dr. Klotzbach – Dr. Gray has been in that fight a lot longer and is the main target.
You might worry about Colorado State – they’ve never been great defenders of The Tropical Meteorology Project and seem to have little interest in defending them or helping attract grant money.
I was never close to the details, and haven’t remembered much, but after some NSF money was reduced, AIG – Lexington Insurance came up with some support. I’m especially fuzzy on these details, but I think some post docs left around then, seeding the NHC’s hurricane prediction effort. Chris Landsea is also a CSU alumnus and is rebuilding the historical hurricane record from contemporaneous accounts from ship logs and newspaper reports.
John Peter above at 3.03a.m. comments on the Louise Gray article in today’s Telegraph. Here in Dublin, Ireland, the same article is reproduced in the Irish Independent this morning 11 June 2010. I cannot ever imagine the Jet Stream taking orders from us mere mortals. We didn’t actually know it existed until the early 1940s. However, my comment here refers to the last few of lines of this article which read: Quote; Prof Andrew Watson, of the University of East Anglia, said the extreme events are “fairly consistent with the IPCC reports and what 99 per cent of the scientists believe to be happening”. end quote. Um, the last time I believed in anything emanating from the UEA was NEVER. After the recent Climategate saga which we all know about, would you believe anything that came from one of their spokespersons?
I also find the part which says that “99% of scientists believe to be happening”
Um, again. I remember 30 to 40 years ago the only people who managed to get 99% support in anything, including a country’s General election, were the likes of Dictators who might alledgelly have opposition. Some of them actually managed to get 101% of the vote on the odd occasion. 99% is so far fetched that I suggest that you recount your figures in order to find the other missing 1%. It’s there, believe me and you can and will find it. If you can’t find it, then ask Phil where he hid it.
I don’t despair at these people’s attitudes, I just with they would “get real”.
Maybe one day, one of these dendrochronologists will see the wood for the trees!
Professor Watson, if by any chance you are reading this, please have a look at the International Climate Science Coalition site and see how many mainstream scientists, REAL Scientists, have signed up to the Manhattan Declaration.
OOPS, I can’t spell allegedly, by the looks of it!
PW