The latest Colorado State forecast for the upcoming Atlantic hurricane season is out, and the story hasn’t changed much from the previous forecast.
The April 2013 forecast calls for Net Tropical Cyclone activity to be 175% of the long-term Atlantic average, bordering on what could be a hyper-active season. Klotzbach and Gray site 2 major factors behind this bullish outlook:
1. The tropical north Atlantic is unusually warm for this time of year. Hurricanes are oceanic heat-engines, and they need fuel. Warm sea surface temperatures provide that fuel. The warmer the water, the more energy can be absorbed and released by hurricanes. So far this winter/spring, the Atlantic is well above normal and this temperature profile compares to some of the most active seasons on record.
Take a look at the attached chart above, showing some previous hurricane seasonal clustering work vs. observed values so far in the Tropical North Atlantic. The SST profile compares closely to seasonal Cluster 6, which has only 4 similar seasons in the historical record going back to 1950. Those seasons are: 1969, 1998, 2005 and 2010. On average, those hurricane seasons had an average ACE (Accumulated Cyclone Energy) index of 188% of the long-term average, and represent some of the most active years on record.
2. El Nino is not expected to develop by hurricane season. For reasons we don’t understand, water temperatures in the equatorial Pacific sometimes get unusually warm. When that happens over a period of time in the summer months, an “El Nino” can develop. When an El Nino occurs, conditions across the tropical East Pacific become very favorable for hurricane activity. The corresponding shift in the upper wind patterns make conditions less favorable in the Atlantic.
The best available model guidance suggests that we will not see an El Nino develop this summer.
As a result, the combination of very warm Atlantic temperatures and no El Nino could lead to a historically active season. This is far from certain, however, and a lot can change over the next few months. Regardless of how busy this season is, it only takes one hurricane to make it a bad hurricane season for someone.