Disagree with the last sentence: I'm not surprised about why it doesn't happen more often...I'm learning how much of a roulette this is.
But ENSO on the other hand is a bit more involved. Now mind you I'm somewhat content with the simpler answer he gave...and it took me a round about way for Googling: I simply looked to see if stirring a cup of hot water cools it down--and sure enough it does! (Hoping I read it right, lol). So it makes sense that the mire wind that blows the cooler the otherwise warm water! So PSU's simple answer led me to a (hopefully) helpful illustration of what happens. Which now makes the talk of "upwelling" and such make more sense...which is, ironically, not so much of a shallow answer after all.
So Mr. @CAPE, stick that in yer cod