Meteorologists/Traders/Analysts Climate Signals/Forecasts Reference Report
Introduction: El Nino southern oscillation (ENSO) is often the most relied upon climate signal to project seasonal climate patterns all around the globe. ENSO is certainly important especially when stronger El Nino or La Nina are present. However, regional sea surface temperature anomaly (SSTA) patterns such as the Pacific decadal oscillation (PDO), Atlantic multi-decadal oscillation (AMO), Indian Ocean Dipole (IOD), northeast Pacific “warm blob” and North Atlantic Warm Hole (NAWH) are increasingly relevant to generating climate forecasts. A full review is presented.
Pacific Decadal Oscillation: -PDO not strong enough to deliver needed Northwest U.S. wet climate for the next cool season.
The PDO is an ENSO-like pattern of Pacific climate variability. Interestingly, the PDO often runs parallel with ENSO (warm PDO/El Nino and cool PDO/La Nina). The primary climate influence of PDO is on west/northwest North America whereas cool phase encourages a coastal storm-generating upper trough most effective (for wet climate) across the Northwest U.S. and southwest Canada while the warm phase encourages high-pressure ridging on the North America West Coast and the attendant dryness and frequent anomalous warmth. Currently, PDO is in the negative phase. Based on a constructed analog taken from the current long-term climate cycle of the PDO (since the middle 1990’s) the most likely PDO signature into 2022 is the negative cool phase while the outlier forecast is reversal to the warm phase (Fig. 1). A vigorous -PDO would return much-needed wet climate to the Northwest U.S./West Canada sector during the 2021-22 cool season. However, the potential cool phase forecast and associated forecast confidence is too low to project this wet climate possibility (for now).
Fig. 1: Climate Impact Company analog projection of the Pacific decadal oscillation through May of next year indicates the cool phase is most likely.
Atlantic Multi-decadal Oscillation: Brief warm phase to support hurricanes AUG/SEP/OCT.
The AMO is a convenient index to identify climate variability across the North Atlantic basin. The index is a basin-wide phenomenon. Impacts of the AMO include increased number and intensity of hurricanes when in the warm phase, a leading influence on North America and Europe summer climate and modulator of arctic sea ice. Since the mid-to-late 1990’s the warm cycle of the AMO emerged. The warm cycle has led to an uptick in hurricanes over the North Atlantic during the past 25 years. However, while +AMO has been persistent 1995-2010, there has been a tendency for a cooler AMO signature during the past decade. The cooler signature has featured neutral to weak warm phase. A reversal to the cool phase remains rare in the current decadal pattern. The AMO has cooled considerably to neutral phase in recent months similar to about one-half dozen years since 2010. The analog projection indicates modest warming to weak warm phase during the height of North Atlantic tropical cyclone season shifting back to neutral phase for late 2021/early 2022.
Fig. 2: Climate Impact Company analog projection of the Atlantic multi-decadal oscillation through May indicates a generally neutral phase briefly shifts to warm phase for the peak of the North Atlantic tropical cyclone season supporting hurricane development.
Indian Ocean Dipole: Wet climate for Australia ahead.
The Indian Ocean Dipole is based on sustained changes in sea surface temperatures on either side of the tropical Indian Ocean. The IOD regime influences rainfall patterns in East Africa, Southeast Asia and particularly Australia. The current IOD forecast from the Australia Bureau of Meteorology is an evolving negative phase (Fig. 3). The negative phase will enhance wet climate risk across Australia and to a lesser degree Southeast Asia while East Africa is drier.
Fig. 3: The Australia Bureau of Meteorology projects negative phase of the Indian Ocean Dipole ahead promising a wetter climate for Australia.
Northeast Pacific “warm blob”: Weaker character should help to push West U.S. heat waves farther inland for mid-to-late summer.
A persistent zone of surface and subsurface strong anomalous warm ocean water in the northeast Pacific Ocean developed in 2013 reaching maximum intensity in 2014. This feature has been semi-permanent since that time. Initially discovered due to the dramatic influence on marine life in the northeast Pacific, the “warm blob” is attributed to increasing persistence of anomalous high-pressure affecting western North America and contributing to long-term drought. The high-pressure ridge described is often related to anomalous warmth and when strong enough during wintertime can reach across Alaska and cross-polar to Siberia tapping arctic air which can surge into North America leading to “polar vortex” winter patterns as observed in 2013-14/2014-15 and briefly last year related to the Texas arctic outbreak. Currently, the “warm blob” is not as strong as the 2013-2020 climatology (Fig. 4) with some weakening seen in the 30-day change analysis (Fig. 5). The weaker “warm blob” may be related to presence of the cool phase Pacific decadal oscillation (-PDO). The diminished “warm blob” should have a tendency to push additional hot climate events during summer 2021 for the western U.S. farther inland rather than the immediate West Coast.
Fig. 4-5: The Northeast Pacific “warm blob” is not as strong as the 2013-2020 climatology and the 30-day trend is cooler
North Atlantic Warm Hole: Profound influence on East U.S. and Europe/Western Russia summer climate including stalling U.S. East Coast hurricanes.
Since the mid-to-late 1990’s the North Atlantic basin has averaged somewhat warmer than normal. The warm ocean surface has contributed to warming of the northern latitude atmosphere which in-turn has diminished the size of the polar ice cap. As the warming accelerates the rate of ice melt of the Greenland ice sheet has also accelerated. The rapid runoff has collected in the north-central North Atlantic, changing the salinity of that environment, causing a cool pool to develop and set-up a block to the northeastward flowing Gulf Stream. The cool pool of water in an otherwise warm North Atlantic basin was coined by scientists as the North Atlantic Warm Hole. This feature has caused a dramatic influence on North America and Europe climate in recent years. A persistent upper trough has formed over the cool pool of water leading to compensating upper ridge patterns in northeast North America and Eastern Europe. The upper-level ridge patterns have led to mild Northeast U.S. winter seasons, stalling hurricanes during summer once reaching the coast (Harvey and Florence) and increased risk of Europe and/or Western Russia drought. Currently, the NAWH is vividly present southeast of Greenland and has already caused climate extremes in Europe (wet May) leading into the warm season. The upper trough across or near the NAWH has soaked Western Europe and the Black Sea region during late spring while the compensating upper-level ridge over North America has contributed what is likely one of the warmest months of June on record for the U.S. The NAWH is certainly well-intact for summer 2021. Expect more high-pressure ridging and anomalous heat risk for the East U.S. ahead and also the susceptibility for blocking high-pressure to slow tropical cyclones once reaching the U.S. coastline later this summer. Additionally, high-pressure ridging bringing hot and dry weather is likely to develop in Eastern Europe or Western Russia later this summer.
Fig. 6-7: The North Atlantic warm hole (NAWH) is strengthening!