Monday, May 20, 2013

Our Thoughts On Hurricane Season

The 2013 hurricane season officially starts on the Atlantic side on June 1st, less than two weeks away. While the start of the hurricane season is often rather quiet, the ten week window between August 1st and October 15th is often not...and in some cases, that window can extend into late October as it did last year.

Each year, we usually go through a few of the key indicators that can make or break tropical development in the Atlantic basin.  First is the state of the Nino or Nina in the Pacific.  Currently, there's a rather neutral signal -- some slight cooling in the "Nino" parts of the basin but it's not a very strong signal towards colder than average water overall that's indicative of a Nina.

Modeling forecasts suggest neutral conditions in the tropical Pacific continue through the summer, with perhaps some warming....albeit modest...through the summer.  However, most modeling prevents a true Nino from developing this summer.  Some models do try to suggest a modest cool down but the majority fall into the "nada" camp of neutral (not too warm, not too cold).  The Pacific matters as a warmer Pacific pattern can drive unfavorable upper level winds for tropical development in the Atlantic more often than not in the Atlantic.

The consensus of five tropical forecasters is for a season that's slightly more active than the recent 1995-2012 average.  Over that eighteen year window, we've averaged fifteen tropical cyclones, eight of which developed into hurricanes.  This compares to the historical (1800's to now) average of just over ten storms.  The problem with using the historical average going back into the 1800's is the number of storms that may have been missed prior to the satellite era.  It's also comparing an overall norm when the Atlantic runs in cyclical fashion between active warm phases and inactive cool phases, with the ocean currently still residing in an active and relatively warm phase.

The overall season ahead does look to continue the active phase that's ruled the roost since 1995.  We're calling for 17 total tropical cyclones, nine of which become hurricanes, with three majors.  The bulk, as is often the case, lines up in August and September, with twelve storms projected to form.

Seasonal track is subject to variation but the Colorado State forecasts and others do project a heightened risk of a US strike compared to the historical norms.  Part of this is due to higher activity compared to long term averages (more storms, more risk for an East Coast hit), partly also due to atmospheric patterns that can set up a more favorable or unfavorable pattern for East Coast landfalls.  Those patterns are easier to pin down in a four week or less window.  That said, the setup is there for another active season in the Atlantic basin.