Summer 2019 observations reveal a resurgence of Blob-like warm sea surface temperature (SST) anomalies in the Northeast Pacific, similar to the devastating 2013/2014 event. Unlike the original Blob, Blob 2.0 peaked in summer. This study shows that Blob 2.0 resulted from a prolonged weakening of the North Pacific High-Pressure System, reducing surface winds, evaporative cooling, and upper ocean mixing. Warmer waters then reduced low-cloud fraction, creating a positive feedback loop. Atmospheric model simulations, forced with observed SSTs, indicate that remote SST forcing from the central equatorial and subtropical North Pacific contributed to the weakened High. This multifaceted analysis clarifies the physical drivers of summertime North Pacific marine heatwaves.

Dillon J. Amaya, Arthur J. Miller, Shang-Ping Xie, Yu Kosaka