SAM refers to the Southern Annular Mode.
It is the belt of westerly winds (Roaring Forties and Furious Fifties) between Australia And Antartica and can be a swell driver in the cooler months.
In a negative SAM the winds and low pressure systems are closer to Australia and so winter swell can be more consistent and/or larger.
Video shows surfing with a negative SAM, in smallish surf in a couple of plastic wavesports, and also home made jobs, but allergic to changing the paddle.
Hope you are getting some fun water time.