Motivated by increasing marine heatwaves (MHWs) and their dramatic climate effects, we analyze the persistent 2019–2020 MHW, which showed significant positive sea surface temperature (SST) anomalies in the Northeast Pacific. Four SST peaks were identified during its evolution, which appeared in November 2019, April, July, and November 2020. Positive temperature anomalies were mostly located within the mixed layer for the first‐year winter peak. However, the warm core was centered around 50 m below (at the bottom of) the mixed layer for the summer (second‐year winter) peak. The dominant factor for the two wintertime peaks was a surface heat flux anomaly, with reduction in evaporative cooling due to the easterly anomaly. The heat flux and potentially the vertical entrainment combined to induce the peak in spring. In the tropical Pacific, a La Niña event occurred following this MHW, while other recorded double‐peak events were associated with El Niño or neutral conditions.

In recent years, the predominant marine heatwaves in Northeast Pacific, the so‐called warm blobs, have exerted substantial environmental and socioeconomic influences on North America and its coastal waters. We select the historical warm blob events from 1951 to 2018 and divide them into double‐peak and single‐peak categories by their seasonal evolutions. The heat budget analyses attribute the leading contributor of double‐peak warm blobs to the surface heat flux at the first wintertime maximum while the vertical entrainment and diffusion take responsibility for the second peak 5 months later. The positive net heat flux anomalies indicate less heat loss from ocean to the atmosphere due to an exceptionally anomalous high as the northern lobe of the North Pacific Oscillation and intensive easterly anomalies, which counteract with the climatological westerlies. For the single‐peak category, the vertical entrainment and diffusion primarily trigger the warm blob and also lead to its termination. Moreover, the single‐peak warm blob induces positive sea surface temperature (SST) anomalies near the Baja California and establishes the Pacific Meridional Mode as the oceanic bridge to convey its influence onto the tropics and trigger the following El Niño around 10 months after the peak. In addition, the subsurface processes, such as the trade wind charging mechanism, also play an essential part by bringing warmer water upwards to the surface and hence cause the positive SST anomalies in equatorial central‐eastern Pacific. However, the interim connection between the double‐peak warm blob and El Niño is not very clear although their intensities appear to be stronger.

Based on ensemble numerical simulations, we find that possible responses of Sandy‐like superstorms under the influence of a substantially warmer Atlantic Ocean bifurcate into two groups. In the first group, storms are similar to present‐day Sandy from genesis to extratropical transition, except they are much stronger, with peak Power Destructive Index (PDI) increased by 50–80%, heavy rain by 30–50%, and maximum storm size (MSS) approximately doubled. In the second group, storms amplify substantially over the interior of the Atlantic warm pool, with peak PDI increased by 100–160%, heavy rain by 70–180%, and MSS more than tripled compared to present‐day Superstorm Sandy. These storms when exiting the warm pool, recurve northeastward out to sea, subsequently interact with the developing midlatitude storm by mutual counterclockwise rotation around each other and eventually amplify into a severe Northeastern coastal storm, making landfall over the extreme northeastern regions from Maine to Nova Scotia.

Using the daily mean anomalies of atmospheric variables from the NCEP Reanalysis-1 (NCEP R1), this study reveals the connection between anomalous zonal activities of the South Asian high (SAH) and Eurasian climate anomalies in boreal summer. An analysis of variance identifies two major domains with larger geopotential height variability located in the eastern and western flanks of the SAH at around 100 and 150 hPa, respectively. For both eastern and western domains, extreme events are selected during 1981–2014 when normalized height anomalies are greater than 1.0 (less than −1.0) standard deviation for at least 10 consecutive days. Based on these events, four SAH modes that include strong and weak Tibetan modes (STM and WTM, respectively) and strong and weak Iranian modes (SIM and WIM, respectively) are defined to depict the zonal SAH features. The positive composite in the eastern (western) domain indicates the STM (SIM) manifests a robust wavelike pattern with an anomalous low at 150 hPa, and surface cold and wet anomalies over Mongolia and northern China (Kazakhstan and western Siberia) are surrounded by three anomalous highs at 150 hPa and surface warm and dry anomalies over Eurasia. Opposite distributions are also evident in the negative composites of the two domains (WTM and WIM). The surface air temperature anomalies are the downward extension of an anomalous air column aloft while the precipitation anomalies are directly associated with the height anomalies above the air column.