WPAC's recon era (ended in 1987) coincided with ATL's inactive period (ended in the early 90s), which would be another possible explanation why WPAC loses to ATL only after it is no longer covered by recon.
Besides, tropical cyclone activity of the two basins seems to be inversely correlated. During La Nina events, ATL becomes more active while WPAC tends to produce weak, short-liivd storms. Meanwhile, during El Nino events, ATL becomes inactive while WPAC tends to produce strong, long-lived storms. That would explain why WPAC loses to ATL instead of the other basins.
And, even WPAC had been covered by recon in these four years, it would still have been ATL's victory, given that WPAC was defeated by a large margin (30 units in 1998, 68 units in 1999, 44 units in 2010 and 81 units in 2017).
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