Emmett_Brown wrote:If you look at a longer range chart of the AMO, there are often pockets of cool years within an overall warm trend. For example, there was a pronounced 2-3 year dip into negative values in the late 1940s during the last positive AMO. It returned to positive until the 1960s, before finally flipping to negative, and staying mostly negative until the mid 1990's. So, we could easily see a return to the positive AMO before it finally ends in another decade or so. Or, this could indeed be the end of the recent positive AMO... But if so, that would make the recent positive AMO shorter than the previous cycle by about a decade. Also, 2017 had an ACE of 225, which is not characteristic of cold AMO (as CyclonicFury pointed out)
Klotzbach & I have been debating the AMO status (still warm or transitioning to cool) for the past 6 years. I was on the side of the recent cooling being only temporary. Phil wasn't so sure - more seasons were needed to confirm. We've come to an agreement that there was a shift in 2013 to a cool AMO. There are active periods even in cool AMO cycles, particularly during the transition years. It would be a relatively short warm AMO, but we've never seen such a long period of cool AMO during the previous warm cycles. During a cool cycle, there isn't necessarily a drop-off in numbers, but there is a decline in stronger hurricanes. We saw that last season, with only 2 majors forming. Will that continue? I think it will this year.