Marine Heat Wave-Inspired High-pressure Ridge Leads to Argentina Drought/Triggers Chile Fires. Heat wave shifts to Argentina next week! El Nino is approaching!
Fig. 1-4: The Southwest South Atlantic marine heat wave located east of Argentina, the 30-day SSTA change and the attendant summer-long high-pressure ridge recently shifting toward Chile.
Discussion: A marine heat wave (MHW) is a large area of warmer than normal sea surface temperatures (SST). Depending on duration, MHW’s can have significant vertical extent, up to 300 meters observed during recent northeastern Pacific MHW episodes. A long duration MHW is the result of climate change although full explanation of that evolution is not well-understood (yet). The MWH east of Argentina is semi-permanent, present most of the past decade. The Southwest South Atlantic MHW is vividly present in the latest SSTA anomaly analysis (Fig. 1) and intensifying based on the 30-day SSTA change (Fig. 2). Meteorologically, MHW is extremely important. There is a strong tendency for amplified broad-scale upper-level high-pressure ridge areas to form across and downwind MWH episodes. No exception is the exposure South America has to this phenomenon as meteorological summer 2022-23 has produced a titanic upper-level ridge east of Argentina extending across Argentina (Fig. 3) to cause drought in that country and aggravate long-term drought in Chile. More recently, the MHW-driven upper ridge shifted westward causing a heat wave in Chile triggering widespread and devastating wildfires (Fig. 4).
The upper ridge causing the Chile heat wave has shifted farther west today although with increased intensity (Fig. 5). The upper ridge shifts back to Argentina later next week when already hot weather becomes more extreme. Next Thursday afternoon, GFS projects afternoon high temperatures >20F hotter than normal (Fig. 6).
Fig. 5-6: The GFS 500 MB anomaly forecast for today across South America and the GFS temperature anomaly forecast for next Thursday afternoon in Argentina.
In a related note, the warming of SSTA off the West Coast of South America the past 4-6 weeks has suddenly and vividly extended to the Nino12 SSTA region. The Nino12 SSTA is now +1.14C (Fig. 7) which is nearly 2C warmer than 30 days ago (Fig. 8). Some forecast models are predicting El Nino coming on as early as April or May and current observational trend certainly confirms that opinion! ECMWF indicates a full-blown El Nino by June (Fig. 9).
Fig. 7-8: The Nino12 daily SSTA analysis and 30-day change.
Fig. 9: ECMWF global SSTA forecast for June 2023.