Others in the sold-out crowd wielded umbrellas, at least until ordered to put them down by security.
"That guy is the most underpaid man here today," one American fan was heard to remark about the hapless bouncer lumbered with the task.
The avenue's famous trees themselves also came in handy for some punters, who huddled beneath them, trading off having a view with not getting soaked through.
But once Morrison strode out at exactly 3pm and launched into the instrumental Celtic Swing, the elements were the last thing on anybody's mind.
It was a treat to have The Man back home, even if every other gig Morrison plays these days seems to be a 'homecoming' of some sort.
In the past few years, he's turned up everywhere from the Harp Bar to the Odyssey Arena, the Slieve Donard Hotel to Dunluce Castle, not to mention his old school, Orangefield High.
Yet it never dims the public's enthusiasm to see the singer, and as he enters his eighth decade, there may be a realisation that precious time is indeed slipping away, as the song goes.
The birthday boy didn't perform that one yesterday, but his 90-minute set was packed with hits and more than a few rarities.
Moondance, Brown Eyed Girl and Days Like This ticked the box marked 'crowd favourites', though they were given the same enthusiastic treatment as when Morrison indulged himself on covers of Mose Allison's Parchman Farm and Guitar Slim's The Things That I Used to Do.
Meanwhile, Close Enough for Jazz could have been an instruction to the drenched throng: "No use feeling sad/No use staying mad/Better when you're glad/You can be there in a heartbeat."
Highlights of the show were the appearances of PJ Proby and Chris Farlowe on tracks from Morrison's Duets: Re-Working the Catalogue album, which, the ever canny muso noted, he is "still promoting".
Proby (76) and Farlowe (74) belted out their lines like the 1960s never ended, and a clearly delighted Morrison allowed himself a chuckle when Proby embraced him on his way off stage.
Alas, Whenever God Shines His Light didn't feature a guest spot from Cliff Richard, but Morrison's backing vocalist filled the gap admirably.
As things wound down, Morrison delivered an epic And the Healing Has Begun, with the line "And we'll walk down the avenue again," eliciting warm cheers from an eclectic gathering.
The audience ranged from Sex and the City star Kim Cattrall to a who's who of the DUP (this writer counted four of their MPs and MLAs enjoying a day off).
There's sometimes a sense that these 'landmark' events mean more to the people organising and attending them than they do to Morrison himself, but he was in fine form yesterday, even cracking a joke about the Dalai Lama at one point.
The sound was clear and sharp, if a little thin and not massively loud, though the ambient staging - including a backdrop of a forest behind the band - made up for any aural inadequacies at the concert.
Fans were lined up Cyprus Avenue to North Road, and local residents had made the most of the occasion, erecting gazebos, bouncy castles and, in one case, a pop-up pub in their front gardens.
In typically cantankerous fashion, Morrison deigned to play the song Cyprus Avenue, but he did namecheck the street of his childhood adventures in Ballerina's closing bars.
"New York City - it's a long way from Cyprus Avenue," he improvised to great effect.
The encore was a transfixing version of In the Garden, and then, job done, the newly septuagenarian star disappeared, leaving his drummer to ask the audience for their appreciation for "Van Morrison" - or as he swiftly corrected himself, "Sir Van Morrison".
The set list
Close Enough for Jazz
Whatever Happened to
PJ Proby? (with PJ Proby)
Born to Sing (with Chris
Sometimes I Feel like a
Mystic of the East
Brown Eyed Girl
Days Like This
Baby, Please Don’t Go
Sometimes We Cry
Whenever God Shines
The Things That I Used to Do
And the Healing Has Begun
In the Garden
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