Marine Heat Waves Shape Prevailing Weather Patterns

Discussion: Since 2000 marine heat waves have increased especially since 2010. Most famous is the emergence of the “warm blob” in the northeast Pacific in 2013 which not only caused dramatic warming at the surface but also to several hundred feet in depth. Other “warm blobs” east of Australia and New Zealand are routinely monitored for their strength, persistence and influence on weather and climate.

The large “warm blobs” of ocean water are linked to persistent high-pressure ridge patterns in the atmosphere which in-turn are compensated for by frequently equally intense upper trough patterns. Depending on the amplitude of these compensating upper air features, the influence can extend around the hemisphere shaping the prevailing weather patterns somewhat independent of ENSO. Consequently, monitoring areas of “warm blobs” becomes essential for explaining and forecasting prevailing climate.

Currently, the prominent Northeast Pacific “warm blob” has shifted westward to near the Dateline to the northwest of Hawaii. The westward shift (with intensity) is the farthest western shift of the past almost 10 years. To compensate for the western shift of this large mass of warm water the Gulf of Alaska has turned cooler than normal and the coolest since 2012. The cool SSTA pattern in the Gulf of Alaska arcs southeastward to the West Coast of the U.S. and southwestward to the south of Hawaii characteristic of cool phase Pacific decadal oscillation (-PDO) and attendant developing La Nina. The evolution of the contrasting SSTA pattern described has left the Northeast Pacific open to vigorous storms (two 945 MB low-pressure systems last week) and waves of much-needed rain/snow for the Northwest U.S. to northern California.

The “warm blob” east of Australia and New Zealand leaves that zone beneath anomalous high-pressure compensated for by a persistent longwave upper trough across Southern Australia which is likely to produce a wet late spring for that continent.

Note that other regions of warm SSTA off the East Coast of Asia, the Northeast U.S., Southwest Europe and east of Argentina are all linked to prevailing upper-level high-pressure ridge patterns the past 30+ days.

La Nina is developing for 2021 into 2022 but mid-latitude SSTA patterns reign as important influencing prevailing weather patterns.