With the North Atlantic hurricane season still waiting for a named storm, and the rest of the globe cyclonically challenged during the past several months, it is a good time to catch up on the research end of things. In terms of papers during the past 6-8 months, the amount of tropical cyclone and climate literature has largely dropped off compared to the heyday after Katrina. Regardless, the following is an “omnibus” style blog posting and can serve as the obligatory 2009 Atlantic Hurricanes posting.
First, the forecasts for the upcoming Atlantic hurricane season are decidedly below-normal or below median or less-active depending upon the metric or audience. The UK Met Office, which recently had its climate research budget slashed 25%, has determined the most likely amount of storms is 6, very low compared to what has been seen since the active period in the Atlantic began in 1995. The most likely Accumulated Cyclone Energy (ACE) tally is predicted to be 60, which is in the basement compared to recent seasons.
Here is a helpful comparison of previous seasons of ACE that I plotted up from the HURDAT best-track dataset maintained by the friendly folks at the hurricane center and NOAA.
NOAA: 9-14 named storms (including Baby Whirls), 4-7 hurricanes (1-3 major) and ACE of about 65-125. The ranges are rather large with NOAA forecasts, and the previous 5-6 years’ forecasts have an uncanny resemblance to each other; they are essentially the same forecast year after year.
Gray and Dr. Phil Klotzbach (CSU, June 2 update): 11 named storms, 5 hurricanes (2-major), and an ACE of 85.
Here is a flavoring of the latter’s reasoning:
We expect current neutral ENSO conditions to persist or perhaps transition to weak El Niño conditions by the most active portion of this year’s hurricane season (August-October). If El Niño conditions develop, it would tend to increase the levels of vertical wind shear and decrease the levels of Atlantic hurricane activity. Another reason for our forecast reduction is due to the persistence of anomalously cool sea surface temperatures in the tropical Atlantic. Cooler waters are associated with dynamic and thermodynamic factors that are less conducive for an active Atlantic hurricane season. Another factor in our forecast reduction is the stronger-than-normal Azores High during April-May. Stronger high pressure typically results in stronger trade winds that are commonly associated with less active hurricane seasons.
Secondly, Global tropical cyclone activity (or hurricane, typhoon, cyclone) has continued to plummet to levels now approaching 50-year lows. There is no mystery why this is occurring: it is entirely natural and associated strongly with the fluctuations of large-scale climate including the well-known El Nino – Southern Oscillation. The extended and powerful La Nina period beginning in 2007 precipitated the downturn in global TC activity as measured by ACE. One ENSO index called the MEI highlights the recent strong La Nina and the last few months tick up to more neutral/warm conditions.
Now, when you take a gander at the global ACE using a 24-month running sum, it is rather apparent that there is a strong relationship. Why do I use a 24-month running sum? The time scale of El Nino events is typically 2-7 years, and more importantly, the Southern Hemisphere tropical season peaks in boreal winter. Thus, if you use calendar year January-December metrics, you necessarily chop off or alias the seasonal activity into unrealistic combinations. Thus, the 24-month sums are smoother but no data is removed, it is raw. Additional details are at my FSU website and a recent GRL article I published in March 2009: Northern Hemisphere Tropical Cyclone Activity.
The current global TC ACE number valid for July 1, 2009 summing the previous 24-months is 1083, and the Northern Hemisphere number is 802. For the calendar year 2009, Northern Hemisphere (NH) ACE is at 33 which is at about 50% of the previous 30-year average. This is not unusual as some Western Pacific typhoon and Eastern Pacific hurricane seasons don’t ramp up until mid- to late-July. However, this is little reason to believe above average NH for 2009 is in the cards.
A discerning eye will see that there is no trend in the Northern Hemisphere ACE during the past 50-years even considering that there is a void of Eastern Pacific and Northern Indian Ocean data prior to about 1970. The global data prior to 1970 also suffers from poor intensity estimates in the Southern Hemisphere when/where satellite observations were very limited. Interestingly, one satellite image was from 40-years ago from the Apollo moon-landing (the Lost Tapes have been found!).
The world faces a growing risk of “abrupt and irreversible climatic shifts” as fallout from global warming hits faster than expected, according to research by international scientists released Thursday.
Global surface and ocean temperatures, sea levels, extreme climate events, and the retreat of Arctic sea ice have all significantly picked up more pace than experts predicted only a couple of years ago.
Figure 6: (A) The numbers of North Atlantic tropical cyclones for each maximum wind speed shown on the horizontal axis. The most intense (Category 5) tropical cyclones have maximum wind speeds of 70 m/s or greater. (B) The proportional increase by cyclone (hurricane) category (1 – least intense; 5 – most intense) arising from increases in maximum wind speeds of 1, 3 and 5 m/s. Note the disproportionately large increase in the most intense tropical cyclones with modest increases in maximum wind speed, compared to the increase in less intense cyclones (23).
After a little digging, reference number 23 points to the talk Dr. Holland gave in Copenhagen back in March, right before Roger Pielke. Here is the extended PDF document.
Figure 1 of the extended abstract shows the maximum intensity distribution of Atlantic tropical cyclones for the period of 1945-2007. He states that theory suggests a potential 1-5 m/s increase in hurricane intensity for a concomitant increase of 1 degree C in ocean temperatures. Quoting: “The impact of a uniform 1, 3 and 5 ms-1 increase in these intensities is shown in Fig. 1b. Quite modest changes of < 20% are indicated for category 1-3 and even category 4 hurricanes. These changes are small compared to interannual variability and would be difficult to detect. But the most intense, category 5 hurricanes could experience an amplified response, doubling in number for a general 5 m/s increase."
Where does Figure 1b come from? It is simply moving the PDF to the right, apparently the tail is a function of the mean. Anyone have an issue with doing that? Just warming up. Figure 2 shows observational proof of this previous hypothesis:
Whoa! Category 5’s have increased by 300-400%! Holland goes on:
Although this example has only considered Atlantic hurricanes, we suggest that the overall result is robust and applicable more widely to weather extremes. Major difficulties arise from the relative rarity and patchy nature of weather extremes and from the inability of current climate models to simulate them.
This seemingly is the converse to the Baby Whirl detection issue brought up here at Climate Audit. The discovery of Category 5 hurricanes in the past is likely a function of our detection capabilities which have markedly improved during the past several decades. Thus, as with Baby Whirls, plotting up Category 5’s as detection has improved apparently will give you hockey stick looking graphs.
Holland points out that changes in the tracks of hurricanes may lead to more Category 5’s, which he alleges are climate signals. Unfortunately, there is no breakdown of natural variability versus climate change / global warming presented. Instead, we are urged to consult the “purely statistical reasoning” in Figure 1, which “implies that other physical factors are contributing to a skewing of the distribution”.
I do not buy the assumption that the PDF of maximum hurricane intensity will simply shift to the right, and I do not find the analysis a “tentative confirmation of (Holland’s) hypothesis.” Furthermore, this analysis is not yet in the peer-reviewed literature.
Lastly, as entertainment value, the Weather Channel on June 30th is going to focus on the “skill” of “hot models” (not Maxim but HWRF) with regards to hurricane forecasting. One such HWRF forecast run of invest 93L in the Caribbean was really out to lunch. Here is the landfall location and an animation to the model run. To be fair, HWRF is “experimental” but it is astounding that it can be so wrong. A trained forecaster would immediately discount this run.
Note: This is NOT a current forecast. The circulation never developed into a tropical storm.
Horribly blown forecast animation for June 27, 2009 00Z forecast.
Couldn’t think of a better selling point for Congressman Alan Grayson (D) and his proposed $50 million U Central Florida / Obama Hurricane Center in Orlando FL, which was added as a Christmas tree ornament in the climate change bill passed by the House of Reps late Friday.
Congressman Grayson said, “With this one move, Central Florida will become a world leader in 21st century meteorology.”