The 2004 Hurricane Season

This report, prepared by the Analysis and Forecast Administration of the National Meteorological Institute (IMN), ascribed to MINAE, is the first update to climate behavior for 2004 and was issued on March 23.

The document drew on the following information sources: a) Regarding the upcoming hurricane season, similar years to 2004 were considered, based on the results obtained in April 2004 (latest version) by a research group from the University of Colorado, USA, led by Dr. William Gray (hereinafter Gray, 2004); b) For rainfall estimates during 2004 and the beginning of the rainy season in Costa Rica, analyses of similar years obtained by the Central America Climate Forum were used; c) The results of the following seven long-term numerical models from NOAA’s Climate Diagnostic Center were analyzed: CCA, NCEP, IRI, LIM, NSIPP, CPC and the model of the European Centre For Medium-range Weather Forecast (ECMWF); and, e) Databases from both IMN and NOAA were also used.

In this manner, the overall behavior of the 2004 hurricane activity over the Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico has been analyzed, as well as the development of the phenomenon known as El Niño/Southern Oscillation (ENSO).

Historical records show that certain years have global oceanic and atmospheric trends, similar to the ones likely to be observed during the last semester of this year. According to Gray, 1958, 1961, 1980 and 2001 are analog years to 2004, and were used to forecast seasonal hurricanes during this year.

Table 1 shows estimates for the 2004 hurricane season, in comparison to the behavior of the previous year’s activity.

Table 1 includes the 2004 seasonal hurricane forecast, the 2003 season, and the cyclone activity for the period between 1950 and 2002. Estimates were made for the Atlantic Basin, which includes the Caribbean Sea, the Atlantic Ocean and the Gulf of Mexico.

The 1958 hurricane season –which produced a total of 10 tropical cyclones-, began on June 14 with Tropical Storm Alma and ended on October 13 with Tropical Storm Janice. Subsequently, during the 1961 season 11 tropical cyclones were registered from July 20 through November 8.

The 1980 hurricane season produced 11 tropical cyclones between July 31 and November 27. Finally, during the 2001 hurricane activity –which began on June 5 and ended on December 4- a total of 15 tropical cyclones were registered.

It is important to point out that the annual average during these four years (1958, 1961 1980 and 2001) is 11.8 tropical cyclones throughout the Atlantic Basin. However, their distribution was uneven. The most active season of these four was in 2001.

This suggests that if analog years correctly anticipate the cyclone activity for this year, at least two tropical cyclones are expected to take place between June and November over the Caribbean Sea, which will also affect, to a certain extent, the Central American Pacific coast.

Hurricane seasons officially start on June 1 and end on November 30.

Trends of El Niño/Southern Oscillation (ENSO)

The 2003-2004 ENSO phenomenon is currently at a neutral stage. The main characteristic of the variables that distinguish it has been their high level of variance during recent months. However, ENSO is currently considered to be in a neutral phase.

Most climate models estimate that these neutral conditions will remain at least during the next 3 to 6 months. IMN issues an ENSO bulletin on a monthly basis (which can be viewed at www.imn.ac.cr, bulletin’s section) which includes updated information about its current situation.

For further information please contact:
Werner Stolz España, wstolz@imn.ac.cr
Officer
Analysis and Forecast Administration, IMN
Juan Carlos Fallas Sojo, jcfallas@imn.ac.cr
Officer
Information and Marketing Administration

1-The Central American Climate Forum is a group of meteorological experts of which IMN is an active participant.
NOAA stands for the US National Oceanic and Atmospheric Administration.
2- The ENSO phenomenon has two different phases: El Niño, which is a warm stage, and La Niña, a cooler stage. ENSO is related to the warming or cooling of the tropical waters of the Pacific Ocean.