Those who follow North Pacific temperature patterns closely are well aware that the past summer brought a dramatic expansion of above-normal temperatures at the ocean surface across the northern North Pacific Ocean, reversing the cold anomalies that developed last winter during the strong El Niño episode. The two maps below illustrate the change, based on OIv2 SST data. The late winter pattern was very characteristic of the positive PDO phase, but by late summer the PDO index dropped to near-neutral and the pattern more closely resembled the positive NPM (North Pacific Mode) phase, i.e. “the blob” pattern.
Here’s a chart showing the monthly NPM index since 2010, based on ERSSTv4 data. Remarkably, the negative NPM episode of late winter, related to El Niño, proved to be very short-lived, and the index is already back up to the strongly positive territory of 2013-2015.
The map below shows the average sea-level pressure…
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