This has been a remarkable hurricane season indeed! Not only have several extremely damaging hurricanes pummeled the U.S., Central America and Caribbean nations, but for the first time ever, we've run out of proper names for these storms. However, perhaps the most curious hurricane of 2005 is one that received little attention. Any idea as to which one?


This has been some year for hurricanes! We still have a couple of weeks left (officially) in the hurricane season, and we've already run through the abbreviated alphabet of hurricane names. For the first time ever, we're now using the Greek alphabet to name storms (see the Science Question of the Week from 2 weeks ago). The next tropical storm to form will be called Hurricane Gamma, which sounds like someone's grandmother.

Even though there has been more than 20 named tropical storms and or hurricanes in 2005, several of which were among the most powerful ever observed, perhaps the most eccentric storm of the season never made it closer than about 3,000 miles (4,800 km) to the States. It formed and remained north of the Tropic of Cancer (23 1/2 degrees north latitude).

In the Atlantic Basin, hurricanes tend to "breed" in the Caribbean Sea, the Gulf of Mexico, in the west Atlantic (near the Bahamas), and off the west coast of Africa (near the Cape Verde Islands).
Atmospheric currents are normally what guide hurricanes. In the absence of upper atmospheric steering currents, "canes" will wobble about as Bob Dylan wrote, "with no direction known." Once a tropical depression forms and grows, the trade winds initially push them along. These trades blow basically from east to west along either side of the equator. If and when a storm leaves the tropics, in most cases it'll interact with the zone of mid latitude westerly winds (prevailing westerlies) and quickly be tugged eastward.

Early and late in the hurricane season (June and October and November), the prevailing westerly winds are positioned more southerly and closer to the equator. Mid latitude weather patterns are typically more vigorous in late spring and early fall than they are in mid and late summer. As a result, in October and November, hurricanes are more likely to curve to the northwest or north after first moving westward from their inception area. In mid season (August-September), when the westerlies are weaker and located more poleward, hurricanes are more apt to drift westward for a longer period before bending northwestward.

Water temperatures in the open Atlantic during late summer and early autumn, south of about 20 degrees north latitude, are generally over 80 degrees F (26 degrees C), and water in the Gulf Stream (near Florida) and in the Gulf of Mexico can on occasion exceed 90 degrees F (32 degrees C). Tropical storms discovering warm water sources are able to maintain and even increase their energy level, providing that their atmospheric environment is supportive -- little or no wind shear (change of wind speed or direction with altitude).

In the east Atlantic off the coast of Spain, the water temperature may be less than 70 degrees F (22 degrees C), even in late summer. Any "cane" venturing into these relatively cool waters will, as a rule, quickly be sapped of its strength. Even if the ocean water is sufficiently warm when a hurricane leaves the tropics, wind shear usually increases, which acts to disrupt the organization of the eye. The combination of cooler water and wind shear is a death knell to hurricanes. Since hurricanes were first tracked and recorded, any aberrant storm curving far enough north to be ushered eastward by the prevailing westerlies, toward the Iberian Peninsula for instance, has petered out well before making landfall. Until this year that is.

In early October, a tropical depression happened to form well north of the Cape Verde Islands, between the Azore and Canary Islands (close to 30 degrees north latitude). This depression deepened and gathered strength, becoming the 20th named storm of the season -- Vince. Despite foundering in cooler water (23-25 degrees C), Vince strengthened to a hurricane and headed toward Portugal, courtesy of a branch of the subtropical jet stream -- yep, Vinnie and the Jets. Maximum sustained winds were just 75 miles per hour and the central barometric pressure was only 987 millibars (29.15 inches). "Normal" air pressure at sea level is 29.92 inches. In both size and strength, Vinnie was a puny fella. For comparison, Katrina's central pressure was 897 millibars (26.51 inches) and peak winds gusted to over 200 miles per hour!

Despite its small status, Hurricane Vince was unprecedented. According to Atlantic pilot charts, which contain over 100 years of compiled data, no hurricane had ever trekked so close to the European continent. Computer models had a hard time dealing with Vinnie since unlike nearly all other storms having a definitive eye, Vince was borne from a cold core system and slowly acquired tropical characteristics. It was essentially a hybrid system. It did in fact reach the Iberian Peninsula, but had weakened considerable when it did so and was no longer a hurricane.

Actually, Vince isn't the first hybrid or strange hurricane to make the news in recent years. In late March of 2004, a hurricane formed off the east coast of South America and subsequently came ashore in southern Brazil. It's believed that this was the first time a storm reaching hurricane intensity developed in the South Atlantic Ocean -- it possessed tropical as well as extratropical characteristics. Because hurricanes here are so rare, there's not even a list to name them.

In late January and early February of 1992, a bizarre typhoon formed in the central Pacific Ocean, in close proximity to the Equator. Because there's so little "spin" between about 5 degrees south and 5 degrees north latitude, it was though that hurricanes or typhoons wouldn't develop in the vicinity of the Equator -- the Coriolis Force is 0 at 0 degrees latitude. However, this didn't stop Hurricane Ekeka. Though Ekeka was purely of tropical origin, it was indeed a curious storm inasmuch as it was the first Pacific tropical storm, during the satellite era, to have formed in the month of January and the first known to have occurred within 5 degrees of the Equator. It formed near 4 degrees north latitude (close to Christmas Island) and was classified a category 1 hurricane at 6 degrees north latitude.

For more about hurricanes and Hurricane Vince, see the below web sites:

http://www.nhc.noaa.gov/

http://www.nhc.noaa.gov/archive/2005/VINCE.shtml?

http://www.nhc.noaa.gov/archive/2005/VINCE_graphics.shtml

http://thestormtrack.com/archives/2005/10/hurricane_vince.html

See also the Science Question of the Week for October 21 2005:

http://www.gsfc.nasa.gov/scienceques2005/20051021.htm

This week's question comes from Dr. James Foster. Dr. Foster originated this series and did it as a solo project for the GSFC website for SEVEN YEARS! Two years ago, Dr. Foster has decided to share the enthusiasm he has for this project with other Goddard scientists and will be posing questions on a semi-regular basis.