It has been a fast start to the 2003 Atlantic Hurricane Season. In a year were La Nina apparently seemed to be the dominant force, seven tropical disturbances have developed including three depressions, four named storms, and two hurricanes. One of these storms formed as early as April.
Then, in one of the most active Julys on record, there were two depressions and two hurricanes. This resulted in some forecasters to be more optimistic in terms of the numbers of named storms, hurricanes and major hurricanes. Issuing, an update to its pre-season forecast, NOAA, indicated that the season would still be above average while Dr. Gray and his team at Colorado State felt it would only be slightly above average.
The first week of August was yet to see a named storm. A tropical low had threatened to become a depression or storm during the weekend of August 1st, 2003, but fizzled. Another wave in the North Atlantic showed no signs of development, and both the Gulf and Caribbean were unusually quiet. All in all, it added up to a slow start to what is supposed to be the most active part of the hurricane season, the Cape Verde Season.
While it has only been a week into August, there are these facts: 1.) Tropical formation and development gradually begins to increase during the month of August, 2.) Cape Verde storms become more prevalent, and 3.) We've already seen a great deal more activity during the first two months of the season than we've had in previous years.
So, the fact that we are ending the first week of one of the more active months of the hurricane season without a named storm is quite surprising. It's not that there hasn't been any activity at all. We have had a couple tropical lows form along with numerous waves, but none of them were able to get organized and strong enough to become either a depression or named storm.
One of the disturbances that really stood out, and had a chance to develop into a storm was a tropical wave that formed in the Central Atlantic during the weekend of August 2-3, 2003. It was a very strong tropical wave with a well defined circulation. However, it just couldn't seem to get its act going. Every time it appeared to show signs of becoming a storm, it would either lose its convection, or organization.This is what makes the development of a tropical depression, storm, or hurricane so special. On average, there are approximately 100 tropical waves that spin off the coast of Africa each year. Only about 10 make it to be a named storm, and about six reach at least minimal hurricane strength. So, our short story about the recent tropical low shouldn't at all be that unusual. Nevertheless, with the flurry of activity early on in the season, it was interesting to see that the disturbance faltered.
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Should we blame La Nina for this? Well, partly. La Nina, is a global climate phenomena that forms in the same region as El Nino, but its different in nature. As a matter of fact, it is the exact opposite of El Nino. What we mean by that is that in El Nino years, sea surface temperatures in the Eastern and Central Pacific are much lower than normal, which in turn works with the Southern Oscillation to lessen upwelling to shift global weather patterns.
For instance, in places such as Indonesia, which usually gets tremendous amounts of rain during the summer months, dry conditions prevail, which can produce severe drought and brush fires. Meanwhile, in the Central Pacific, which is usually dry, very rainy conditions prevail with higher than average rainfall. On the flip side, La Nina produces cooler than normal sea surface temperatures, and that shifts the weather patterns in a different way.
This year, it has been very hot and dry in the Western United States and Europe while it has been wet and cool in the Eastern portion of the United States. A similar thing happened in the Eastern United States in 1996, and that was during a recent La Nina episode. During El Nino years, tropical activity in the Atlantic Basin is usually below normal because upper level winds become much more hostile toward development. Hurricanes, which are vertically stacked systems, need to have light winds aloft in order to grow and mature.
On the other hand, during La Nina years, upper level winds are less hostile and more conducive toward tropical development in the Atlantic. So, when forecasters indicated that a La Nina event was developing, and pre-season Atlantic Hurricane numbers were optimistic, it seemed we were in for a very active year. The events that have occurred from April up to now have supported that.
However, recently, evidence has suggested that the La Nina episode was not as strong as originally forecasted, and we apparently are headed into a normal climate phase. There also has been some suggestion that another episode of the Madden-Julian oscillation is occurring, and that has impeded hurricane development in previous years such as in the summer of 2000.
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Summarizing the 2003 Atlantic Hurricane Season as of the time of this report, we have had already four named storms, and two hurricanes including Hurricane Claudette, which was nearly a Category Two Hurricane prior to landfall. In addition, there have been also three tropical depressions: Tropical Depression Two, Tropical Depression Six, and Tropical Depression Seven.
According to the Monthly Summary for July 2003 by NOAA, an average year would have seen only 1.6 named storms, and 0.6 hurricanes by the end of July. Meanwhile, forecasters at NOAA have indicated that the 2003 season will be above average with between 12 to 15 named storms, 7 to 9 named storms, and 3 to 4 hurricanes, which is slightly higher than what they forecasted in May, 2003. Slightly in contrast, Dr. William Gray and his team of forecasters were not as optimistic.
Although their numbers for named storms (14), hurricanes (8), and major hurricanes (3), were the same as earlier in the year, Gray's forecast lowered its net tropical activity rating from to 120 from 145. Finally, NEMAS, which issued its first ever seasonal hurricane forecast, projected 15 named storms, 10 hurricanes, and 5 hurricanes in an above average year.
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