La Niña conditions developed earlier this autumn, and are expected to persist through the winter according to the Climate Prediction Center. These conditions, which are characterized by below-average sea surface temperatures (SSTs) in the central and eastern equatorial Pacific, will lead to a wide range of impacts to global weather patterns for as long as they persist. But while La Niña will grab the headlines, SST variations or anomalies (SSTA) on a comparatively smaller scale can also have major impacts on regional weather patterns as well.
For instance, over the past couple of decades the prevalence of marine heat waves has increased dramatically, and this is now a rapidly growing area of research against a background trend of global ocean warming. Generally, warmer SSTs influence weather patterns and make some weather events more extreme. Marine heatwaves are prolonged periods of warmer than usual ocean temperatures (basically akin to what a heat wave in the weather is) within a specific region. These are commonly termed “warm blobs,” and have impacts on downstream weather patterns that can overshadow the effects of larger-scale teleconnections such as ENSO which we detailed in an earlier blog in January 2021 on teleconnections and extended range forecasting.
Currently, multiple warm blobs exist around the world, including in the northwest and southwest Atlantic. But as shown in Figure 1, arguably the most notable warm blob exists in the north central and eastern Pacific. As recently as August, this blob was concentrated in the NE Pacific, but by October had drifted west to become centred near the International Date Line (IDL). Meanwhile, a cold pool has developed in the Gulf of Alaska in its place. Also note the expansion of the below normal SSTs in the eastern and central equatorial Pacific, emblematic of the development of La Niña conditions.
Figure 1. Average SSTs for August 2021 (Top) and October 2021 (Bottom). Source: Climate.gov
The contrast between the warm blob in the central North Pacific and the cold pool in the Gulf of Alaska has helped facilitate the creation of strong baroclinic zones near the boundary between the two features with dramatic impact on prevailing weather patterns. Baroclinic zones are areas with temperature gradients that exist on constant pressure surfaces, and these zones can be favourable areas for strengthening weather systems. The westward shift of the NE Pacific “warm blob” to the IDL compensated for by the coolest Gulf of Alaska SSTA pattern since 2012 has contributed to increased storm tracks in the North Pacific. This was covered by an earlier FW blog covering ‘bombogenesis‘ issued 29 October 21 where one storm set a new record low atmospheric pressure and generated hurricane force winds and significant wave heights greater than 10 meters.
Unlike air temperatures, SSTs are slow to change. As a result, a similar pattern persists in the North Pacific to this day, as shown in Figure 2.
Figure 2. Current SST Anomalies, as of 18z on 08 November 2021. Source: Tropical Tidbits
This pattern will continue to provide favourable conditions for the formation of additional gales and/or more extreme storms in the north-central and northeast Pacific, especially as we continue to transition into the active winter season.
Here at Fleetweather, we will continue to monitor the region for adverse weather that could impact trans-Pacific shipping routes.
Stay connected and safe.