Hurricane Season 2004

We're into the last half of May now, and that means Hurrican Season is coming soon and the National Hurricane Center's hurricane predictions are in.

This year's storm names:
Alex, Bonnie Charley, Danielle, Earl, Frances, Gaston, Hermine, Ivan, Jeanne, Karl, Lisa, Matthew, Nicole, Otto, Paula, Richard, Shary, Tomas, Virginie, Walter.

Some highlights from the NHC's predictions:

The outlook calls for 12-15 tropical storms, with 6-8 becoming hurricanes, and 2-4 of these becoming major hurricanes. These numbers reflect a predicted ACE index in the range of 100%-160% of the median, and indicate a likely continuation of above-normal activity that began in 1995.
Many of the tropical storms and hurricanes in 2004 are likely to form during August-October over the tropical Atlantic and Caribbean Sea between 9°N-21.5°N (green box). These systems generally track westward toward the United States and Caribbean Sea as they strengthen.
Another factor known to significantly impact seasonal Atlantic hurricane activity is ENSO (Gray 1984, Monthly Weather Review), with El Niño favoring reduced activity and La Niña favoring increased activity. Based on the most recent ENSO outlook issued by NOAA's Climate Prediction Center, ENSO-neutral conditions are expected to continue in the tropical Pacific through July, and most likely through August-October as well. However, there is considerable uncertainty in the statistical and coupled model ENSO forecasts after July, and the comparatively wide range in the predicted ACE values reflects this uncertainty.
There are two competing uncertainties in this outlook. The first is the possibility of an extremely active season similar to 2003, which resulted partly from near-record warmth across the deep tropical Atlantic, and partly from an amplified upper-level ridge across the western subtropical Atlantic and Gulf of Mexico in association with a persistent East Atlantic teleconnection pattern (Bell et al. 2004, Bull. Amer. Meteor. Soc., In press). In the event that the warmer tropical Atlantic SSTs and the subtropical ridge over the western Atlantic again become significantly enhanced, the ACE values could be at or even above the high end of the predicted range.

The second uncertainty involves the ENSO forecasts, which have exhibited low skill historically when issued at this time of the year and represent an ongoing source of uncertainty in the pre-season hurricane outlooks. There is currently considerably diversity in the statistical and coupled model forecasts of ENSO after July, which leads to a wider predicted ACE range in this outlook.

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