I think this trough in the central Atlantic is not that uncommon for La Nina years. If you look at the previous La Nina years since 1995 during our current active cycle only 2007 failed to have any significant recurving systems in the central Atlantic. 1995 was the extreme with a major weakness throughout the entire active part of the season. We have had cases such as 1998 when the trough started out the month of August and had a few systems recurve but then switched to a strong ridge in mid September that allowed Hurricane Georges to slip through.
1995
1998
1999
2000
2007
Now if we look at the NAO graphic below it is interesting that all the previous La Nina years fell into postive NAO territory for the year so this year will be outside of the trend if it continues to feature a negative NAO. It will be interesting to see if this trough stays in place.
