Seasonal forecasts for the Atlantic 2008 hurricane season

The 2008 hurricane season for the Atlantic Ocean

It’s going to be a modestly more active than average Atlantic hurricane season in 2008


It’s going to be a modestly more active than average Atlantic hurricane season in 2008, according to the December seasonal forecast issued by Dr. William Gray and Phil Klotzbach of Colorado State University (CSU). The CSU team is calling for 13 named storms, 7 hurricanes, 3 intense hurricanes, and an ACE index 20% above average (Accumulated Cyclone Energy (ACE) is a measure of the total destructive power of a hurricane season, based on the number of days strong winds are observed). An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The CSU forecast calls for a 15% above average chance of a major hurricane hitting the U.S. The odds for a major East Coast hurricane are put at 37% (a 31% chance is average), and odds for the Gulf Coast are 36% (30% chance is average). The CSU team predicts that the current moderate La Nina event will weaken by the 2008 hurricane season, but still contribute to lower than average values of wind shear. In addition, warm sea surface temperatures are likely to continue in the tropical and North Atlantic during 2008, due to the fact that we are in a positive phase of the Atlantic Multidecadal Oscillation (AMO), which began in 1995.

The forecasters examined the observed atmospheric conditions and ocean temperatures in October-November 2007, and came up with a list of five past years that had a similar combination of a moderate La Nina event, near average tropical Atlantic sea surface temperatures (SSTs), and warm far North Atlantic SSTs. Expect 2008 to be similar to the average of these five analogue years, they say. The five years were 2000 (14 named storms, 8 hurricanes, 3 intense hurricanes), 1999 (12, 8, and 5 of the same), 1989 (11, 7 and 2), 1956 (8, 4 and 2), and 1953 (14, 6 and 4). Hurricane Hugo of 1989 (Category 4) was the strongest hurricane to hit the U.S. in these five analogue years.

2008 storm names

The following names will be used for named storms that form in the North Atlantic in 2008:

Arthur, Bertha, Cristobal, Dolly, Edouard, Fay, Gustav, Hanna, Ike, Josephine, Kyle, Laura, Marco, Nana, Omar, Paloma, Rene, Sally,Teddy, Vicky, Wilfred.

The names not retired from this list will be used again in the 2014 season. The list is the same as the 2002 list except for Ike and Laura which will replace Isidore and Lili, respectively.

Predictions

The studied parameters are in particular:

  • Geopotential altitude of isobar surface 500 hecto Pascals (or atmospheric pressure around 5500 meters of altitude) on Atlantic North and also in the North-West of North America;
  • Atmospheric pressure on the sea level on the tropical zone of the North-eastern Pacific Ocean;
  • Temperature of the surface of the sea in the north of the Atlantic Ocean
  • Change of the temperatures of the surface of the sea close of the equator in the central and Eastern Peaceful Basin: what provides an indication of the phase La Niña or El Niño.

Currently, one is located rather in a moderate phase of La Niña, which should continue in 2008, and which causes to increase the cyclonic activity on our areas of the Atlantic.

The conditions of observation

According to the anomalies compared to the seasonal average of these various parameters, P. Klotzbach and W. Gray seek the years in the past closest to these conditions observed: years 1952, 1955, 1988, 1998 and 1999 were appointed. And thus, starting from the activity observed during the years which followed (1953, 1956, 1989, 1999, 2000), they calculate how will be, during the summer 2008 on the zone of the Atlantic, the winds trade winds (around 600/800 m of altitude), the winds in high troposphere (around 12000 m of altitude), the temperature of the sea, the barometric pressures of surface.

All these weather parameters should be, according to them, rather favorable to the formation of the tropical cyclones. The figures selected then are a scientist proportioning between the average of the activity observed during the above mentioned similar years, together with a coefficient of adjustment to hold account of the strong activity noted since 1995 on the areas considered (due to 20/30 years a natural cycle already highlighted).

General tendency of these statistics

Of course, and let us not hesitate to point out it, it is necessary to take these figures as what they are, results of the theoretical studies at statistical base, and to be satisfied to interpret them like a general tendency, without retaining the exact values of them. The more so as it is known that the assessments of end of the year are generally quite different from these figures announced at the beginning of season.

In 2005, as in 2006, and even still for the past year 2007, the forecasts were rather far away from reality all the same: a large undervaluation in 2005, an over-estimate in 2006 and even in 2007…. But one can however announce that in the current state of knowledge of the atmosphere during the autumn 2007, of many indices agree so that one can expect one year cyclonic 2008 on the Atlantic rather active, but a little less than the 13 last years average.

Probabilities of the affected territories

These are finally probabilities that certain territories will be affected by an intense hurricane in 2008:

  • American Coasts (all the Mexican border in Canada): 60 % (average over 100 years: 52 %)
  • Atlantic American Coasts (of the south of Florida in Canada): 37 % (average 31 %)
  • American Coasts of the Gulf of Mexico (Texas - Florida): 36 % (average 30 %)
  • Risk higher than the average for the islands and territories of the Caribbean and the Bahamas.