Hurricanes 2006

Nathan Todd Cool, Chief Forecaster, WetSand.com
April 5, 2006
See also: Global Warming Percolates Long Range Surf Forecasts

During the second week of October in 2005, only a couple weeks after Hurricane Rita slammed the Louisiana coast—a region still recuperating after the devastation from Hurricane Katrina—something strange was going on in the Atlantic that caught the attention of meteorologists at the National Hurricane Center. An unusually large, monsoon-like circulation and a broad area of disturbed weather were developing over much of the entire Caribbean Sea, spanning far and wide. Mixing with additional disturbed activity known as tropical waves, over a period of a few days this behemoth storm continued to grow. By noon on October 15th, this storm, that would soon break records unimaginable, became cyclonic and acquired its birth status as an official tropical depression. Two days later, this storm was given a name: Wilma, a storm that would break the Atlantic record with an amazing 882 millibars of pressure. But this was only one record broken last year, and the Gulf Coast is still pick up the pieces from an overly active hurriane season. Unfortunately, 2005 does not look like a one-time fluke of nature.

There’s no doubt that 2005 will go down in history as a record-breaking year for hurricane, and it also looks like 2006 could be a close runner up. All the conditions are lining up for another active hurricane season in at least the Atlantic, and one forecasting expert is warning that this year could be a doosey.

Dr. William Gray, Professor of Atmospheric Science at Colorado State University has analyzed previous hurricane seasons for over 23 years and compiled predictions for upcoming periods. By looking at conditions in the past to those at present, Gray has done a fairly good job at coming up with a reasonable outlook for hurricane seasons that lie ahead. On April 4, 2006, Gray confirmed his original forecast from late 2005 regarding the 2006 Atlantic hurricane season, and the prognosis was not good.

Gray’s recent forecast calls for 17 named storms in 2006; a normal year has around 9. He also calls for the number of hurricanes to reach 9 versus the normal 5, and that we will likely see 5 intense hurricanes versus the usual 2. While the National Hurricane Center has yet to release their projections for 2006, Gray’s forecast does seem viable given the factors at play in the Atlantic region and world climate in general. But, Gray has been known to get it wrong from time to time.

Gray did a pretty darn good job at forecasting what we can expect in forthcoming hurricane seasons up until 2004 and 2005, when the Atlantic fooled everyone. Gray has yet to submit any of his findings for peer-review or official publication, which has brought him criticism from many in the scientific community. Nevertheless, his forecasts have been viewed by many to be credible, given the fact that he does derive his findings from 52 years worth of data, which has proven to be somewhat successful. For instance, when predicting the 2003 hurricane season in late 2002, Gray forecast that the Atlantic would produce 12 named storms, and sure enough, there were 14—pretty darn close. He also predicted that same year would see 3 intense hurricanes, and once again, his prediction was accurate with exactly 3 intense hurricanes in 2003. Prior years were also predicted with similar accuracy. The 2004 season was also similar with initial predictions made in late 2003 calling for 13 named storms, and sure enough 14 named storms developed in 2004. But when it came to intense storms, his initial prediction for 2004 came in at only 3, when that year actually produced twice as many monster hurricanes.

And then, 2005 got the best of everyone, including Professor Gray. His prediction in late 2004 for only 11 named storms in 2005 was way off compared to the actual 27. And as for intense hurricanes, his prediction of only 3 was far surpassed by an occurrence of an astonishing 7 massive storms—more than twice that of his original forecast. Gray does tighten up his forecasts as the clock ticks down and months get closer to the actual hurricane season, yet even in his updated report in the beginning of October of 2005, he had only predicted 20 named storms—still 7 shy of the grand tally that year.

Given Gray’s recent track record of lower expectations, one has to wonder if we may see a more intense hurricane season in the Atlantic in 2006. After all, elements are in place to fuel hurricane ferocity this year. Water temps continue to be above normal, although around this time last year, Atlantic water temps were about 1°C above normal, while now they’re running about 0.3°C to 0.5°C above average. Hurricanes need warm water to form, and these anomalous temperatures work like jet fuel inside of a cyclone.

In addition to the above normal sea surface temperatures, a warm, deep-water ocean current in the Gulf of Mexico known as the Loop Current may likely still be positioned favorably for hurricane intensification. This current, which comes up from between Cuba and the Yucatan peninsula, moves north into the Gulf of Mexico, likely helped to fuel Katrina, Rita, and Wilma by giving these storms warm water from lower ocean depths. Typically, when a hurricane grows, it sucks up more and more water from below it. If this well of water below the hurricane is relatively cool, then it literally cools off the hurricane as it’s sucked into the cyclone. The Loop Current though, being a flow of warm water far beneath the surface of the ocean, is just what a hurricane needs to grow. In 2004 and 2005, it’s believed that the Loop Current was a bit stronger, but this mysterious ocean circulation continues to elude predictability, and science has yet to link its changes definitively to any particular phenomena. Nevertheless, we do know that one of the influences placed on the deadly three of 2005—Katrina, Rita, and Wilma—was the warm waters of the Loop Current. All three of these systems passed over the warm depths from the Loop Current, and like a boost of steroids, the Loop Current pumped these hurricanes into ominously sized, savage, ocean-originating storms. We may see this happen again in the 2006 season if hurricanes get driven into the Gulf region.

Other factors will need to be observed as the hurricane season draws near including the position of the Bermuda high, which can spin storms at the U.S coastline. High-pressure systems in the northern hemisphere spin clockwise, and the Bermuda High is no different. As this massive high-pressure system spins, hurricanes passing under it get caught in the periphery of its circulation and get steered one way or another. If the Bermuda High is small, and located where it normally is, passing hurricanes caught in the spin of the Bermuda High are thrown northward, thus being diverted away from a direct hit on the east coast of the U.S. But in 2005 and in 2004, the Bermuda High was not sitting in its usual position. With its leading edge precariously close to the east coast, the Bermuda High was swinging incoming hurricanes directly at America’s eastern seaboard and the Gulf of Mexico. At this point in time, it’s difficult to say exactly how the Bermuda High will act in the coming months, and it, along with such things are the African Easterly Jet (AEJ) will need to be monitored to see how hurricane trajectories could play out.

One factor we do know of that will add to hurricane ferocity is that we’re now in a La Niña condition. During this cycle of the ENSO, the jet stream is placed just so to reduce the amount of upper atmospheric winds over hurricane alley. This reduces what’s known as vertical wind shear, which can make or break a hurricane trying to form. In this condition, winds at higher elevations are blowing so much stronger than winds below, that rising hurricane columns are literally sheared off once encountering the stronger high elevation winds, thus killing the hurricane itself. In a La Niña cycle, this wind shear is reduced, which can result in vigorous hurricanes climbing to powerful heights and strengths.

After enduring two intense hurricane years in 2004 and 2005, and now that we’re facing yet another humdinger of a year, one may wonder if global warming is afoot, and partly responsible for this activity. This is a highly debated subject, which I discussed in my previous article . Professor Gray, an ardent skeptic on climate change, has criticized peer-reviewed work from others like Kerry Emanuel from MIT mentioned in my previous article, stating that Emanuel’s links of climate change to hurricane ferocity, “...is wrong, it’s just wrong.” Gray contends that recent hurricane intensification is linked to the great ocean conveyor known as the thermohaline circulation (THC), which transports warm water northward. This circulation, which is fueled by salinity differences in ocean water, while being linked to decadal oscillations, can indeed be influenced by melting freshwater from glaciers and sea ice (things that are happening now in a warming world). Gray however, doesn’t see a link, while others in the scientific community do. In fact, we do know that the THC completely stopped 12,800 years ago, during a cold snap known as the Younger-Dryas. We also know that prior to this ice age, there was a warming period where massive amounts of fresh water poured into the oceans from melting glaciers and sea ice. This meltwater slowed the THC until it finally stopped moving altogether. And now, global temperatures are on the rise, and glaciers are melting at breakneck speed, thus contradicting Gray’s belief that the THC has nothing to do with a warming world.

Still, Gray is right in saying that we are in a decadal oscillation. NOAA in fact published an article in November of 2005 where they concluded that the recent upswing in hurricane activity was “not related to increases in greenhouse gas warming.” Their explanation was that a decadal oscillation known as “the tropical multi-decadal signal” was to blame. According to NOAA, a positive cycle of this oscillation began in 1995. But what they didn’t mention in this particular article was an index they use in the forecasting process, which shows something anomalous about the recent hurricane trend, and global warming.

Using a strength index called the Accumulated Cyclone Energy index (ACE) NOAA can observe decadal oscillations related to hurricane seasons. The ACE shows a busy, positive cycle from 1950 to 1970, then a slowdown into a negative cycle from 1971 to 1994. And it certainly shows an active, positive decadal cycle starting in 1995 to now. NOAA mentions that the positive cycle from 1950 to 1970 started to repeat itself in 1995 after it flip-flopped to a negative cycle from 1971 to 1994. This makes perfect sense. This is what multi-decadal oscillations do; however, the ACE index shows that our recent positive cycle that started in 1995 is stronger than the cycle from 1950 to 1970. So while we indeed appear to be in a positive decadal cycle, this cycle is stronger than those we’ve previously seen in the past, which is suspicious in a warming world.

The intense decadal cycle we’re in now (shown in NOAA’s ACE index) corresponds to the research I mentioned in my previous article that was conducted by Kerry Emanuel of MIT and a team of researchers from the National Center for Atmospheric Research and the Georgia Institute of Technology, which Professor Gray waves off as unfounded. Still, there’s no doubt that we are in a positive decadal oscillation, yet there is also no doubt that our current oscillation is stronger than before.

Whether or not there is a link to global warming and recent upswings in hurricane ferocity, everyone is in agreement that 2006 will most definitely be a busy hurricane season in the Atlantic. Living in a zero-sum world where things tend to reach equilibrium, we could expect a non-active hurricane season in the eastern Pacific. Yet, sea surface temperatures are on the rise most everywhere--something that is being linked to human-induced climate change. Nevertheless, the Atlantic has many more bellwethers showing a very active hurricane season for 2006. While the debates continue over climate change and links to human-induced global warming, we do know that Mother Nature’s elements are coming together this year to increase the risk of property damage and loss of human life along hurricane-prone regions of the United States. This fact alone must not be ignored, no matter what the underlying cause may be. There is just too much at stake. Caution and preparedness will undoubtedly be paramount this year, as will continued monitoring of climatic progress in the Atlantic and around the globe.

--Nathan Cool

Nathan Cool is the founder of WaveCast, the Chief Forecaster for WetSand.com, and the author of many books including The WetSand WaveCast Guide to Surf Forecasting and most recently, Rhythm of the Ocean. More information on Nathan can be found at his web site:
http://nathancool.com/

To read Nathan's previous article on global warming links to surf seasons and hurricane intensifications, Click Here.

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