Executive summary: La Nina Modoki is rare! The last fortified La Nina Modoki occurred during quarter 1 of 1989. The climate patterns for quarter 1 of 1989 associated with this ENSO regime were generally much different from conventional La Nina. The La Nina Modoki favors a drier climate in South America and Australia and shifts typical storm tracks for mid-to-late winter across the U.S. while favoring a colder climate. The La Nina Modoki climate anomalies identified may not be exactly as indicated given the much warmer global oceans of the modern-day climate.
La Nina Modoki SSTA discussion: La Nina Modoki is present when the cool SSTA pattern in the equatorial East Pacific shifts westward toward the Dateline. La Nina Modoki events are rare. The last well-developed La Nina was during quarter 1 of 1989 peaking during February (Fig. 1). At that time a strong cool-biased SSTA pattern hovered near the Dateline while waters off the northwest coast of South America were slightly warmer-than-normal. A conventional La Nina occurs when the cool-biased sea surface temperature anomalies (SSTA) stretch across the east-central to far eastern equatorial Pacific Ocean.
Currently, there are signs of a weak La Nina Modoki-like SSTA pattern forming in the equatorial Pacific Ocean. In recent days very warm SSTA across Indonesia has shifted westward well into the tropical Indian Ocean (Fig. 2). Following along are increased trade winds near and just east of the Dateline to up-well cool subsurface waters. Consequently, cool SSTA have generates near and just east of the Dateline while the far eastern equatorial Pacific Ocean is warmer than normal as trade winds are light. The west-shifting SSTA patterns are also evident in the tropical Atlantic where warm-biased SSTA off the West Africa Coast have shifted westward toward the northeast South America Coast.
Note how much warmer the global SSTA pattern is now compared to early 1989!
Fig. 1: Global SSTA analysis for Feb. 1, 1989 when the last fortified La Nina Modoki was present.
Fig. 2: Current global SSTA analysis revealing possible development of La Nina Modoki.
La Nina Modoki climate anomalies discussion: During quarter 1 of 1989 when La Nina Modoki dominated global climate, the South America rainfall pattern featured wet conditions across Paraguay and southwest Brazil while east/northeast Brazil and Argentina were drier-than-normal (Fig. 3). In Australia at that time, dryness dominated northern continent while a wetter-than-normal climate was observed in South and Southeast Australia (Fig. 4). In the U.S., a cold pattern was evident West and Central U.S. while the Southeast was mild (Fig. 5). The storm track was prominently indicated from the Mid-south to the Mid-Atlantic States (Fig. 6).
Fig. 3-4: JAN/FEB/MAR 1989 precipitation anomalies across South America and Australia.
Fig. 5-6: JAN/FEB/MAR 1989 temperature and precipitation anomalies across the U.S.
Typical La Nina climate anomalies discussion: Is the La Nina Modoki climate pattern of quarter 1 of 1989 different from conventional La Nina? The last 5 La Nina episodes produced a wetter climate during mid-to-late summer across Brazil and Argentina is not as dry (Fig. 7). In Australia, conventional La Nina is wetter (Fig. 8). Mid-to-late winter across the U.S. during conventional La Nina is typically mild and dry across the southern states while the Northwest is chilly and Northeast and Northwest are stormy (Fig. 9-10). Typical La Nina is wetter Northwest/Northeast and drier in the South and milder than La Nina Modoki for the U.S.
Fig. 7-8: Precipitation anomalies for quarter 1 of the year during the last 5 conventional La Nina episodes in South America and Australia.
Fig. 9-10: Temperature and precipitation anomalies for quarter 1 of the year during the last 5 conventional La Nina episodes for the U.S.
Summary: La Nina Modoki is rare! The last fortified La Nina Modoki occurred during quarter 1 of 1989. The episode occurred while global oceans were substantially cooler compared to now. Consequently, the La Nina Modoki climate patterns of quarter 1 of 1989 may be different now given the warmer global oceans. However, for comparison-sake of the Q1/1989 La Nina Modoki climate pattern compared to an average of the last 5 La Nina episodes for the same time of year the Brazil climate is less wet and the Argentina climate is drier. In Australia, a drier climate than typical La Nina occurs with La Nina Modoki. The U.S. mid-to-late winter climate is colder (except Southeast States) and wetter in the Mid-south States.
Conclusion: At stake in the months ahead and into early 2022 is whether a significant drought in Brazil can reverse due to La Nina Modoki rains. If so, does Argentina turn dry and become a drought target for summer 2021-22? Based on the evidence provided in this report, southwest Brazil drought eases while drought in the eastern part of the nation continues. Argentina becomes a drought target for summer 2021-22. In Australia where drought has been avoided over 1 year, crop areas should be OK for summer 2021-22 particularly in the Southeast. However, heavy rains sometimes caused by La Nina are not likely. Finally, in the U.S. there is reliance on La Nina climate to bring much-needed precipitation to the Northwest U.S. drought region. La Nina Modoki regimes are not as wet in that region as conventional La Nina. There are large differences in the Mid-south and Northeast U.S. precipitation patterns. The La Nina Modoki favors a drier winter in New England while Arkansas is soaking wet. The La Nina Modoki climate is also colder across much of North America although that analog is likely less reliable given the warmer global oceans of the modern-day climate.