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.
OOPS again,
I gave the date as 11 June. Red faced, iIadmit that this should be 11 August 2010.
Tom_R says:
August 11, 2010 at 6:12 am
You seem to be confused between the Klotzbach/Gray forecasts from CSU and the far less interesting forecasts from the NOAA’s NHC. I would never call Bill Gray part of the bureaucracy and was pleased to be able to finally meet him at this May’s ICCC in Chicago.
The forecasting methodology of the Klotzbach/Gray forecasts is never quite static, but you can read about some of their retrospective testing that Phil mentioned above. Also, page 54 of their latest forecast compares the last six years (four forecasts per year) with final observations. Four were overpredicted, two were underpredicted.
I suspect a surplus of overpredictions may be due to events happening that are hard to predict. El Niño one year shut down the hurricane season early one year, Saharan dust suppress Cape Verde hurricanes another year. Other than an early collapse of El Niño, there aren’t too many surprising events that boost hurricane production.
Please make the plot, but I find the postmortems in the end-of-season summaries a lot more interesting. Let’s just say Gray has learned a lot from decades of trying.
PolishG, I agree with Makarieva et al.
However the Walker circulation is a myth that observation doesn’t support.(read Leroux)
“”” Tom in Texas says:
August 10, 2010 at 7:43 pm
George E. Smith says:
August 10, 2010 at 6:14 pm
“…and I measured SSTs (with an actual real thermometer in the water)…
Did you adjust the data for time-of-day observations?
Tom in Texas says:
August 10, 2010 at 7:48 pm
George E. Smith says:
August 10, 2010 at 6:14 pm
“…and I measured SSTs (with an actual real thermometer in the water)…”
Did you ADD a couple of degrees to adjust for the UHI effect (your boat)? “””
The ONLY thing I adjusted was my glasses; changing from my everyday (driving) glasses to my everyday (Computer) glasses; so I could read the thermometer more clearly. Yes I admit that it would have been bett5er if I used everyday (reading) glasses; but then I don’t actually have any reading glasses; so my computer glasses have to suffice.
I did not make any adjustments for time of day; since the only measurements that I made, were actually made at the time of the day for which I read the thermometer.
Since Mother Gaia adjusts the Temperature to be correct at the time of day for which she adjusts it; then it is appropriate to only measure it for the times that I read the thermometer; so no interpolations or extrapolations are necessary.
And since I did not actually measure the Temperature of the boat, then I had no informatin with which to make any sort of UHI correction. In any case Mexican fishing Pangas are typically colored inside such that they remain actually cooler than the ambient air Temperature; and the only air Temperatures measured were for air over the sea; not air over the boat. The data was noted as read from the instrumentation without any fudge factors being applied.
A good experimentalist (or process engineer) designs his experiments so that his instruments directly measure the variables of interest; rather than measure something else, and then “inferring” the desired data from some assumed proxy relationship.
People who do process control by proxy tend to design things that go ‘boom’ when you least expect it.
Geologists are scientists, and at least 90% of the ones I know think that climatologists are FOS.
Ref – Robert of Ottawa says:
August 10, 2010 at 4:25 pm
“I must say that, contrary to my past life experience, I am finding Russian TV (RT) a bastion of objectivity and news coverage in comparison to the CBC, BBC, ABC, NBC, xBC TV networks”
__________________________
True! This is climate change, not weather.
Ref – Ric Werme says:
August 11, 2010 at 6:23 am
John W. says:
August 11, 2010 at 5:09 am
“Dr. Klotzbach, First, thanks for coming here and providing this information. Hopefully, you won’t receive the same treatment Dr. Curry has received.
“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 have a feeling that the Chinese are already well underway and putting together their own world class Tropical Meteorology Project. Colorado State is fast making themself into just another regional Community College – how the mighty are falling! I guess thumb twittling and day dreaming really can be dangerous.
Thanks for the informative post on the science behind the predictions. I fully support your continued work.
But….I live in Florida and we hear the hurricane forecasts every year with more interest than most. You can quote all the statistics you want, but the hurricane forecasting the last 5 years has been nothing more than a random number generator.
The error margins used are (necessarily) very large and even these are being missed. We basically get a low, medium, high forecast every year and last year was a good example of a forecast of “very high” season which ended up being extremely low (your specific forecasts may be different). This type of miss inspires very little confidence in future forecasts.
I understand the complexity of the problem and the lack of hard historical data in which to derive the true cause / effect relationship of the indicators being measured. Don’t mistake this as criticism, as I haven’t heard any hurricane forecasters making outrageous claims of their forecast’s societal value to this point. It is a very difficult problem.
The main point I want to make is that these simulations require a lot of iterations of test/validate cycles to accurately determine and scale the correct inputs for better results. Because seasonal forecasts only get one set of results per year, the models will struggle to “home in” on a better answer until better input data is available. This may take decades to accumulate. Compare this to the relative luxury weather forecasters have (daily results) and also hurricane track prediction (ten per year).
I have seen this cycle in action over the last twenty years in Florida as hurricane tracking has gotten progressively better every year, and the reliability of the “prediction cone” and spaghetti models is now very good 48 hours out, and this has real value down here.
Don’t feel too disadvantaged though, climate modelers have to wait 30 years to validate their models, and they are making all kinds of unsubstantiated claims about the efficacy of their results.
Thanks Dr Klotzbach for spending the time writing this excellent post.
Dear Dr. Klotzbach
You say: “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 am an applied physicist interested in the hurricane business. I read the paper by Makarieva and Gorshkov in Physics Letters A and I understood very well what they propose as the driving principle: air pressure drop caused by vapor condensation. They nicely demonstrate (albeit in an approximation) that the total pressure fall is a factor of 2.5 times the partial pressure of water vapor, with this additional (geometric) factor caused by radial convergence.
We have phase transition — we have a pressure fall — we have winds. Fullstop. (By the way, I see here a nice analogy to the heat pipes as described by Grover in 1964. These devices employ the same principle to rapidly divert heat due to the fact that the fluid-carrier is accelerated by pressure gradients formed by phase transitions.)
I also tried to find a competitive explanation elsewhere. I read a paper in Physics Today where hurricanes were described as heat engines extracting heat from the ocean. I was taught at school that this is impossible. That the heat content of the oceans, although huge, is useless for ordered processes.
For you as an authority in the field, is it possible to explain to an educated person in numerical terms what determines the pressure fall in the hurricane (this is what Makarieva et al. do very convincingly, in my opinion). Just this question: why does the pressure fall over an area spanning several hundred kilometers by up to 100 mb? Just a quantitative hint? I am a physicist and I cannot see how air pressure can fall due to a “heat input”.
Many thanks in advance.
Regardless of seasonal forecast,and revisions to a forecast, our job in Emergency Management, cannot be predicated on forecast but on the results of an unprepared community. Thank you for your’s and Dr. Grays research.
Tom Scharf
We hear the 30 year climate figure all the time, but the fact is that seasonal forecasts constantly invalidate the climate models.
Peter Walsh says:
August 11, 2010 at 6:33 am
…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.
I don’t know, Peter. 99% of sceintists and engineeers in the defense industry think AGW is junk science.
As Dr. Gray, himself, has said many a time, the bell simply hasn’t rung yet…
polishG says:
August 11, 2010 at 11:22 am
A heat engine needs a source of heat, and sink that is colder. For tropical storms, those are the sea surface and the air above, basically the tropopause. The wind transfer of collecting heat (and latent heat as water vapor) along the surface, conversion of heat energy to mechanical during convection, and subsidence of dry air to complete the cycle is said to be an efficient heat engine. At least by Kerry Emmanuel. He’s gradually learning about the confounding variables that limit the energy a storm can develop. Even surface friction doesn’t introduce inefficiency – any heat released by slowing the wind will evaporate more water.
On the other hand, if you put Emmanuel and Bill Gray in the same room, you may have to announce a storm warning. I think Emmanuel has mellowed a bit, but he’s still mostly a theorist and Gray more an empiricist.
Hurricanes are nature’s way of moving heat quickly from lower latitudes to higher latitudes. The North Atlantic is very warm this summer, so I don’t find the case for a lot of hurricanes to be completely convincing.
If the whole planet had a uniform hot temperature (like Venus) there wouldn’t be a lot of convective storms.
This from Two-Week Forecasts of Atlantic Hurricane Activity (for two-week periods between August and October) http://hurricane.atmos.colostate.edu/Includes/Documents/Two_Week_Forecasts.html
COLORADO STATE UNIVERSITY FORECAST OF ATLANTIC HURRICANE ACTIVITY FROM AUGUST 4 – AUGUST 17, 2010
We expect that the next two weeks will be characterized by heightened amounts (130 percent or more) of activity relative to climatology. These new two-week forecasts have replaced the monthly forecasts that we have been issuing in recent years.
(as of 4 August 2010)
By Philip J. Klotzbach and William M. Gray
This forecast as well as past forecasts and verifications are available online at http://hurricane.atmos.colostate.edu/Forecasts
See “Meteorology for South Florida and the Caribbean”, at http://www.oarval.org/meteorologFL.htm
stevengoddard says:
August 11, 2010 at 4:59 pm
Hurricanes are nature’s way of moving heat quickly from lower latitudes to higher latitudes. The North Atlantic is very warm this summer, so I don’t find the case for a lot of hurricanes to be completely convincing.
===========================================
That should be one of the very reasons that it should be very convincing.
That as well as the sinking cool air in the Pacific in the means due to La Nina has displaced the upward motion east and west, to both the Atlantic and Indian Oceans.
And a uniformly “hot” Atlantic is not a good comparison to the uniformly hot Venus.
For all your extreme smarts, Steve [and I have a lot of respect for those smarts], you may be grasping at straws on this one.
Chris
Norfolk, VA, USA
Ric Werme says:
A heat engine needs a source of heat, and sink that is colder. For tropical storms, those are the sea surface and the air above, basically the tropopause. The wind transfer of collecting heat (and latent heat as water vapor) along the surface, conversion of heat energy to mechanical during convection, and subsidence of dry air to complete the cycle is said to be an efficient heat engine.
Yes, I kind of perceived this idea. I feel really odd that such things could pass as explanations in serious literature (if I got them right — please, tell me if I am wrong). If my student was telling this to me, he would not pass the exam.
A sink and a source of heat do not make a heat engine. There can be a temperature difference with just heat conductivity, no mechanical output. This is what we routinely observe over the ocean — the temperature difference is sitting there (the troposphere is cold at all times) but there are no hurricanes.
Then suddenly there is the same temperature difference, and hurricanes! I ask — why? The message I gathered from the PT article is because heat input has increased due to high wind speeds — and high wind speeds are due to high heat input — but, my apologies, this is exactly what Baron Münchhausen did when getting out of a swamp by pulling his own hair…
It is like saying to guys who exhaust themselves perfecting the technological heat engines — folks, just make the engine move a little, then you get a huge output, because speed enhances heat input and heat input enhances speed, you will be surprised how much output you will get… how much heat you will be able to extract from the sea…
Tell me where I am wrong, would be much appreciated.
Year ASO Nino 2nd Hurricane Formation Date Seasonal ACE
1954 -0.98 8/27 113
This year was one of the most active of recorded history for the East Coast of the US.
Carol, Edna, Hazel [all of those 1950’s names LOL].
2nd hurricane formation was not until the 27th.
polishG says:
August 11, 2010 at 7:09 pm
==================================
I love listening out loud to the mind of a physicist or engineer trying to problem solve.
Fascinating and inspiring at the same time. [I mean that.]
Chris
I found Dr. Klotzbach’s post quite stimulating. I’ve also found some of the comments by other posters interesting.
I do know that most people who focus their attention on tropical cyclone development do not make an automatic correlation between increased global warming and increased number of tropical cyclones. In fact, there is a fair amount of analysis out there that suggests the contrary i.e. few numbers of storms, but greater number of strong storms.
I also had to smile at the person who commented that Russian scientists are more concerned about global cooling, when this summer they are experiencing the worst heat wave in the last 90 years…. perhaps they should have been a bit more concerned about warming trends after all….
However, my attention was drawn most strongly to those who feel it is practically impossible to have 8 hurricanes in 13 weeks, or to have 15 more named storms before the end of November. To illustrate the fallacy of that thinking, consider the 1950 hurricane season. It was one of those selected by Dr. Klotzbach as part of his presentation in the above article. In 1950, there were 13 named storms, 11 of which became hurricanes, 8 of them major hurricanes (cat 3 – 5 winds). Between August 20 and October 21, TEN of those 11 hurricanes had their lives. SEVEN of the 8 majors formed during this time. This happened within a period of eight weeks. We have had seasons where there were four hurricanes at the same time. In 2007, seven storms formed in September alone, three of them hurricanes. And that is not the record for number of named storms in a calender month.
My point is that the history of the Atlantic basin, not even including the so-called “suspect” data of the pre-satellite age, suggests that it is entirely possible for there to be an additional 3 storms this month, an additional 7-10 between now and the end of “all over October”, and possibly as many as two additional storms in November (the Atlantic as seen storms as late as Dec 9 in La Nina years).
While I am not saying that Dr. Kotzbach’s forecast WILL verify, there’s certainly more than enough evidence in the reliable historical record to show that it is well within the realm of possibility.
I also had to smile at the person who commented that Russian scientists are more concerned about global cooling, when this summer they are experiencing the worst heat wave in the last 90 years…. perhaps they should have been a bit more concerned about warming trends after all….
=========================
Good post overall. Although the above words I would disagree with.
We are entering a period of more extremes in climate, so record heat (and cold) (and dry and wet) should not be surprising.
Just because Moscow has endured probably its worst heat wave on record, does not mean that the Russian scientists are not right about global cooling.
Time….and the data….will tell.
Chris
Only by asking the right questions, do you get the right answers,
electromotive ions drive the intensify of the precipitation,
condensation rates drive the pressure drop,
the oceans provide the heat to power the wind driven by convection,
lunar declinational tidal forces move the atmosphere, that steers the storms,
and the outer planets vary the total storm intensity.
It is the relationships of these interactions that determine the outcome,
balmy day with light mist, or angry sea, and winds all pi$$ed.
The mayor of Moscow was bragging last year about how they control the weather through Russian weather modification technology.
Correct. It makes a heat pump.