In fact, the first hurricane in the Atlantic this year, Erin, formed just last Friday. It has been churning in the north Atlantic Ocean and is now no threat to the US mainland. Hurricane Felix, this season's 2nd hurricane, formed a couple of days ago and is near the center of the north Atlantic Ocean, but like Erin it appears to be of little concern to the eastern US. A tropical storm in the eastern Gulf of Mexico, Gabrielle, is now the 8th named storm of the season.

On average, by the end of August, 9 tropical storms and 6 hurricanes form in the Atlantic Ocean, the Caribbean Sea or the Gulf of Mexico. This year there were only 5 tropical storms and no named hurricanes - this was only the 4th time in 50 years that there was no hurricane during the month of August. The last time this happened was last year. However, last year there were 7 hurricanes in the month of September. Between 1995 and 2000, there were 41 hurricanes in the Atlantic Ocean and or Caribbean Sea and Gulf of Mexico, which is the most in any five year period since records were first kept in 1886. Compared to the period from 1971 to 1994, from 1995 to 2000, there was a doubling in overall hurricane activity in the Atlantic Ocean and a 2.5 fold increase in major hurricanes. Additionally, there was a 5 fold increase in hurricanes affecting the Caribbean. A fortuitous dip in the jet stream over the eastern US helped keep most of these hurricanes from clobbering our coasts.

The Tropical Prediction Center in Miami (part of the National Oceanic and Atmospheric Administrations Climate Prediction Center) issues a forecast in May of each year (updated in August) for the expected number and severity of Atlantic and Caribbean hurricanes during the upcoming season. This season was forecast to be an average to an above average year. A similar forecast was made by William Gray and his colleagues at Colorado State University.

While it's true that, world-wide, the 1990s was the warmest decade of the 20th century, and this decade also witnessed an above-normal number of hurricanes, there doesn't appear to be a direct connection between global warming and hurricane frequency or intensity. So, even though the world temperatures may be getting slightly warmer, it doesn't mean that from now on we can expect hurricanes in late summer to bash our shores on a weekly basis.

With hurricanes, thermal energy is converted to powerful winds when evaporated warm, seawater condenses into rain. The tropical Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico, from about late July through September, is nearly always warm enough to support hurricane development. Fortunately, warm water is not the only ingredient necessary for hurricane formation.

Other determinants also effect hurricane development, including atmospheric winds and pressures. Basically, tropical depressions and tropical storms will not evolve into full blown tropical hurricanes, having a stable eye, if winds aloft are not conducive to further development. In other words, if the vertical wind shear across the western, tropical Atlantic Ocean is stronger than normal, storm circulation is more likely to be shut off. This seems to be happening to some degree this year. Stronger-than-average winds aloft deprive developing tropical storms of the environment they require for intensification. An organized system can't form if its intake and outflow mechanisms are compromised.

In general, La Nina weather patterns have been shown to be conducive to Atlantic hurricane development, whereas El Nino patterns have the opposite effect. The cooler Pacific waters that are typical of La Nina years, promote upper-air circulation regimes that are more likely to result in weak winds aloft in the tropical Atlantic. In the case of El Nino circulation, the warmer Pacific temperatures tend to result in increased vertical wind shears over the Atlantic Ocean. However, not every year is either a La Nina year or an El Nino year, and in fact, most years are neither. This is the case this year - the Pacific waters have not been anomalously warm or cool.

An additional consideration is that thus far this season, the upper-air easterly winds (African easterly jet stream) over western Africa don't seem to be particularly favorable for "kick starting" tropical waves or disturbances into weather systems that spin. It's thought that these winds are important for getting energy to weather disturbances as they propagate westward out of west Africa and into the open Atlantic. The frequency of surface dust storms that move out of the Sahara Desert and into the Atlantic Ocean may be an indicator of the vigor of these easterly winds. Of the 8 named tropical systems this season, only 3 have formed off of Africa.

Once they've formed, hurricanes are still difficult to forecast.Though hurricane prediction models are more sophisticated than ever, trying to forecast how many will form a season ahead of time and how powerful they may be is a rather daunting task. Regardless of how elegant the models might be, they're simply mathematical representations that are only approximate descriptions of actual processes. The models can be viewed as a "work-in-progress" to help forecasters better understand the behavior of hurricanes, how they form and where they'll go. Despite the fact that like last year, things have gotten off to a slow start, there are more than 2 months remaining in the current hurricane season - still plenty of time for a nasty hurricane or two to make some noise.

For more about this see the Climate Prediction Web site;
http://www.cpc.noaa.gov/products/outlooks/hurricane.html
and the Earth Science Question for May 25, 2000.