We have passed the statistical peak of the 2002 Hurricane Season, and as of right now, we have seen a good deal more storms than anticipated, but very little in the way of hurricanes and major hurricanes. To date, there have been a total of 11 named storms if you include Subtropical Storm Kyle.
We also have seen a total of 13 depressions this year. However, there have only been two hurricanes so far (Gustav and Isidore), and Isidore remains the only major hurricane of the season so far.
What is the reason for this? El Nino? Madden-Julian? Perhaps, cooler sea surface temperatures in the Atlantic, or the strong Atlantic High Pressure Ridge? The answer could be all of these together. However, if recent history holds true, all of this might not matter.
At the very beginning of the season, the folks at Colorado State University indicated a modest hurricane season with just above average numbers. However, as the season progressed, it seemed apparent that the forecast would change, and it did to only 9 named storms, 6 hurricanes, and 2 major hurricanes.
A lot that has been responsible for this has been a strong ridge of high pressure in the Central Atlantic, which was responsible for much warmer temperatures and higher humidity along the Eastern seaboard this summer. This strong dome of high pressure suppressed thunderstorm development along the ITCZ to the south, and as a result tropical waves were not able to develop any further than they did.
However, in the past month, the high has released its grip, and activity has picked up again with a bulk of the named storms coming since August 20th. This continues a trend that has developed over the past several years with the bulk of tropical activity occurring after August 15th.
The real surprise in these numbers to this point is the fact, that there have only been two hurricanes, Gustav and Isidore. That is well below average relative to the past seven or eight years, and even below Gray's forecast from August, 2002.
While, we're still in the middle of September, and October and November have been surprisingly active over the past three or four seasons, we could be looking at a dearth of hurricanes this year. Nevertheless, it only takes one, and Isidore could be that one.
Several weeks ago, while commemorating the anniversary of Hurricane Andrew hitting South Florida, Jim Williams of Hurricane City had a funny feeling that something big was going to happen this year, and he may be right.
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There have been a number of climatological factors at work this season. While rainfall has been plentiful in Western Africa this year, upper level winds have been very hostile in parts of the Atlantic and Caribbean. This may be due to the effects of the moderate El Nino, which developed earlier this year.
The effects were even supposed to become more of a problem, but so far they have not. As a matter of fact, you could say with recent developments in the tropics that they've relaxed somewhat. Another inhibiting factor could be slightly cooler sea surface temperatures this year in the Atlantic.
In particular, off the coast of Africa, where we have seen a number of very impressive waves just fall apart upon hitting the Eastern Atlantic this season. Probably the biggest factor of all though as been the dominant high pressure ridge in the Central Atlantic.
Much like it has over the past several years, this ridge had a strong reach with 1024 mb pressures near Bermuda while 1016 mb pressures reach as far south as just above the ITCZ. As a result, there was a great deal of sinking air that the tropical waves that were able to survive into the Central Atlantic had to deal with.
You must remember that hurricanes and tropical storms are vertically stacked systems. In other words, thunderstorms need to build vertically in order for the storm to organize and intensify.
The high pressure and sinking air capped thunderstorm development, and pushed activity further south, which also made it difficult because the waves were too far south to have a chance to develop. That is because the trade winds cannot converge effectively to cause a spin or rotation, which is needed for development also.
Could this be another episode of the Madden-Julian Oscillation? Not known for sure, but a couple years ago this oscillation had a tremendous impact on activity, and that same summer high pressure did dominate in the Central Atlantic.
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If Jim Williams is right, and Hurricane Isidore continues to flourish in the Gulf of Mexico, all these numbers aren't going to matter. However, over the past several days a number of tropical disturbances have developed. In addition to Isidore, on Friday, September 20th, a subtropical depression developed in the Central Atlantic less than 1000 miles from Bermuda.
A subtropical system is one that has some tropical characteristics along with some extratropical characteristics. Winds usually do not get stronger than 60 miles per hour, and the storm has more of a mid-latitude cyclonic structure. In addition, subtropical systems are more of a cold core system than a warm core, which means cold air resides around the center of circulation rather than warm air.
This depression became Kyle on Saturday, September 21st, and has 45 mph winds. Nevertheless, it is only a threat to shipping interests in the Northern Atlantic. Meanwhile, another tropical depression developed on the afternoon of Saturday, September 21st, and is already showing signs of becoming a storm. If it does become a storm, it will be named Lili.
There are also two other tropical disturbances currently in the Atlantic, a weak upper level low near the Bahamas, and a tropical wave in the Eastern Atlantic near the Cape Verde islands. if the past several days are any indication of what might happen the rest of the way, then we could be looking at perhaps a more active year than last year.
The big question will be whether or not all of these areas of trouble are going to become hurricanes and major hurricanes. We'll have to wait and see. Anyway, the past several years, there have been a number of strong hurricanes in late September, October, and even November.
For example, in 2000, Hurricane Keith was a Category Four Hurricane that lashed Northern Belize with 135 mph winds in early October, 2000. Later on that month, we had Tropical Storm Leslie, which was originally a subtropical system that brought 15 to 20 inches of rain to parts of South Florida before becoming a tropical storm.
Then, around the same time, Hurricane Michael developed in the Western Atlantic, and eventually brought 100 mph winds to parts of the Canadian Maritimes. The trend didn't stop there. In 2001, Iris was a small, but powerful Category Four Hurricane that ripped through Central Belize with 145 mph winds, and killed 28 people in early October, 2000. Iris was then followed up Michelle in November as a powerful hurricane that brought 135 mph winds to Western Cuba.
You can even go back to before 2000 with powerful hurricanes developing late in the season. In October, 1998, Hurricane Mitch was the most powerful and deadliest storm on record in the month of October as it grew to Category Five strength, and eventually killed 11,000 people in both Honduras and Nicaragua.
Then, a year later, Hurricane Lenny became the most powerful storm in November on record with 150 mph winds. It also had the unique distinction as the first storm ever on record to hit the Lesser Antilles from the West. So, as you can see, if history is right, we may be just seeing the beginning of the 2002 Hurricane Season.
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