That was June 17th. A day before, in India, the same thing happened, also early:
Monsoon covers India by mid-June, earliest everSatellite view of a monsoon
Jun 17, 2013
Monsoon rain has covered the entire country [India] a month ahead of schedule, brightening the prospects for a bumper output of summer-sown crops such as rice, oilseeds and cotton.
The rain usually covers all of India by mid-July, but this year it happened on June 16, the earliest such occurrence on record, a senior official at the India Meteorological Department said."
Is June 17th really "very early" for Korea? I said it was, though I wasn't quite sure of that when I was writing post-89, I must confess. I was just repeating what I'd heard. Now I find a scholarly article (from 2006) that says the onset of the Jang-Ma season in Korea (i.e., the first Monsoon of the year) has always occurred in the window of "late June to mid-July" (after which a few more weeks of regular Monsoons follow). June 17th is outside that window, and two to three weeks earlier than the overall-average onset time of early July. June 11th, the onset date in 2011, is way outside that window.
I wrote, in post-89, that people were "speculating about earlier arrival [of the Monsoon season as] being connected with climate change."
In my hunt for educated-speculation on earlier-Monsoons and climate-change, I find the following from June 25th, 2008 in Bangladesh:
BANGLADESH: Early monsoon floods "point to climate change"
The monsoon floods have come early to Bangladesh, with thousands of people losing their homes and crops to river erosion, in what specialists say is a clear sign of climate change.
Most major flooding in the low-lying nation is not expected until July and August.
"Early flooding of the Ganges and the Brahmaputra rivers is an example of climate change caused by global warming," Atiur Rahman, an environmental economist, told IRIN, noting a gradual advance of the annual flooding over the past 50 years.
All those guidebooks that say Korea's Monsoon season begins in July draw from established knowledge, which may no longer be correct.