The short answer is that, in the long term, shear cannot be forecasted with any reasonable degree of accuracy. It can be implied from expected patterns, but those patterns, e.g. long waves, associated jet streams, etc., can themselves be wrong (and often are at the seasonal level). In the short term (up to three or four days) shear can be predicted with reasonable accuracy at the synoptic scale, but beyond that timeframe the accuracy and value of the forecast deteriorates rapidly. If a seasonal forecast for a region predicts high precipitation, the implication might be for more fronts and low pressure systems in that regon and therefore higher wind shear, but it doesn't always work out that way. Florida gets a lot of thunderstorms in the Summer (and therefore its a normal region of higher precipitation) but thats an expectation associated with temperature and seabreeze, i.e., climatology, rather than fronts and extratropical cyclones.

The SST forecast has changed (as noted in the Storm Forum) but all that really means is that the SST forecast for the Pacific ENSO regions that was made six months ago MAY no longer be accurate (keep in mind that the current forecast may also turn out to be inaccurate and the older forecast could still verify). The current forecast only suggests that any conclusions that may have been implied based on the earlier forecast should be revisited for potential revision.

I personally am not familiar with any accurate long term windshear forecasting technique.
Cheers,
ED