I've recently finished reconstructing the tri-monthly ONI using the CPC's methodology w/ the relatively new ERSSTv4 dataset back to 1870, and a few other years have come up (1905-06, 1914-15, 1940-41, 1941-42) that had El Nino conditions persist through the spring/summer & into the following winter. This 2nd year El Nino is however unique in that we are observing intensification during the spring, and I can only find 2 events in the historical record (1987-88 & 1905-06) w/ similar behavior... Both events had similar peaks in terms of timing & intensity, peaking just above the strong NINO threshold (1.5C (although 1987-88 was still a moderate NINO by Jan Null's 3 successive tri-monthly definition) in the late summer-early fall w/ 1905-06's peak ONI of +1.69C in JAS & 1987-88's +1.57C in ASO. I think this is a reasonable solution to anticipate for now, however only time will tell.