What we're seeing with the SOI is just fluctuational. As JB has even pointed out himself, it's been swinging up and down the past several months. One likely reason for the negative SOI the past week or so is the negative MJO that has been over the Australian/WPAC region. Not only has that enhanced WPAC typhoon activity, but also lowering of pressures over Australia...SOI. Once the positive MJO takes over (which should be rather soon), we'll probably see it swing back to positive again.

On another note, even IF the SOI were to stay negative for a long time...any El Nino that tries to come on will have a hard time. Significant El Nino development in late summer/fall is uncommon, and actually has NEVER occurred in the past 50-60 years or so when the QBO is westerly. The time period to look for El Nino formation is March-May...so AT MOST we'll have a warm-bias ENSO (not really true El Nino) towards the end of the year...too late to have any impact on the hurricane season.