Atlantic and Pacific Subtropical Highs in Mid-May 2026: A Tale of Two Blocking Anticyclones

 

Executive Summary

As of mid-May 2026, the atmospheric circulation of the Northern Hemisphere is dominated by two large, persistent subtropical anticyclones whose behavior is producing strikingly different — and in some ways opposite — regional outcomes. Off the west coast of North America, the North Pacific High (NPH) has anchored an unusually strong, persistent ridge over the eastern Pacific and the western U.S., extending a winter-long blocking pattern into spring. It is deflecting Pacific moisture far north into Alaska and the Gulf of Alaska or shunting it south toward Mexico and the subtropical jet, locking the western United States and western Canada into anomalous heat and worsening drought. Across the Atlantic, the Azores / North Atlantic Subtropical High is in the early stages of its seasonal poleward and westward migration toward its summer (Bermuda High) position; this past winter, however, it sat farther east and weaker than usual, allowing an exceptional run of Atlantic storms to break a seven-year drought in Morocco. Now, with the seasonal Sahara Heat Low strengthening, the subtropical Atlantic High is reasserting subsidence over the northwestern Sahara and limiting moisture incursions, even as the West African monsoon prepares to ramp up to the south. Both systems are operating during an ENSO transition from a just-ended 2025–26 La Niña to a developing El Niño, and both show signatures consistent with multi-decadal trends — Hadley-cell expansion, poleward migration of subtropical highs, and an apparent restructuring of the North American winter waveguide — that peer-reviewed work links explicitly to anthropogenic climate change.

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1. The North Pacific High and Western North America

Current Position and Strength

The North Pacific High in mid-May 2026 is behaving as an unusually strong, persistent, and northward-displaced anticyclone for this time of year. NOAA Ocean Prediction Center high-seas analyses from May 12, 2026 depict a sprawling ridge axis over the central and eastern subtropical North Pacific that, together with anomalous heights over the U.S. West Coast, is forcing the Pacific storm track sharply northward — the OPC's text products place the active storm/gale-warning lows around 53–58°N near the Aleutians (e.g., a 989-mb complex low at 53°N 174°W on May 12) while the area south of about 42°N remains dominated by light winds and the subtropical ridge. Climatologically the NPH at this time of year is just beginning its summer expansion toward 30°–40°N / 140°–150°W; this year, however, mid-troposphere height anomalies have remained large and positive over the eastern Pacific and the interior West more or less continuously since the autumn of 2025.

NOAA confirmed that winter 2025–26 was the warmest on record across the majority of the American West, with seven states setting all-time winter records, several by more than 2 °F. The proximate cause was a near-stationary ridge over (or just inland of) the West Coast — what observers have termed a "Ridiculously Resilient Ridge"-style pattern — that, far from breaking down with the seasonal transition, intensified spectacularly in March 2026 into a record-shattering heat dome over the Southwest. ECMWF, CFSv2, Copernicus, and CanSIPS ensembles entering May continue to depict a "massive upper-level ridge" over the eastern Pacific and U.S. West Coast, with the 250-hPa jet stream split forced around the ridge core: one branch shunted into Alaska, the other displaced south toward Mexico and the southern Plains.

How the NPH Is Blocking and Redirecting Pacific Moisture

The physical geometry is classic anticyclonic blocking. Clockwise circulation around the high accelerates the polar jet poleward on its northern flank, sending Pacific storm systems and their associated atmospheric rivers into the Gulf of Alaska, British Columbia, and Alaska rather than allowing them to make landfall along the Pacific Northwest, California, or the Great Basin. On the southern flank of the ridge, the easterly trade-wind component and the displaced subtropical jet have funneled tropical Pacific moisture eastward across northern Mexico into the southern Plains and Deep South, producing the wet, severe-weather-prone "Ring of Fire" pattern downstream while leaving the West parched. Subsidence under the ridge dries and warms the descending column adiabatically, suppressing convection and clearing skies across the interior West.

A notable wrinkle this spring has been the role of diabatic ridge-building: heavy precipitation events near Hawaii (a deep Kona Low in March produced record-breaking Hawaiian rainfall) released enormous quantities of latent heat that was advected downstream into the Pacific Northwest along atmospheric-river corridors, amplifying the downstream ridge over the West to levels analyst Daniel Swain and others characterized as the most extreme cool-season ridge ever observed over North America. The World Weather Attribution group concluded that the March 2026 western heat wave "would have been virtually impossible without human-induced climate change."

Real-time visualization platforms such as earth.nullschool.net (which renders global GFS-derived MSLP, 500-hPa heights, and wind fields) consistently show this pattern as a broad anticyclonic gyre centered in the eastern subtropical Pacific with a strong, northward-extended ridge axis impinging on the U.S. West Coast — qualitatively matching the NOAA OPC analyses and ensemble depictions cited above, although nullschool's particle-flow visualizations do not provide formal central-pressure values for the high.

Precipitation and Drought Consequences

The blocking has translated directly into severe and worsening hydroclimate stress:

• U.S. Drought Monitor (May 13, 2026 release): 51.35% of the U.S. and Puerto Rico, and 61.47% of the lower 48 states, are in drought (D1 or worse) — approaching the 2012 record. Drought worsened in large parts of the Northwest, Plains, Midwest, and Mid-Atlantic in the week ending May 13.
• Western intensification: Exceptional drought (D4) was expanded in southern Idaho; extreme drought (D3) was introduced in Oregon and expanded in Montana, Idaho, and Nevada. Coastal and Great Basin stations recorded less than one-tenth of an inch of rain in the monitoring week. Localized improvement was seen in southern Arizona, western Nevada, and parts of Wyoming/Colorado where a May snowstorm and showers occurred.
• Snowpack collapse: The March 2026 heat dome triggered a historically unprecedented snow-water-equivalent decline across the Upper Colorado Basin, plunging values far below previous record lows for late March. Across the West, snow cover on December 7, 2025 had been the lowest in the MODIS satellite record for that date.
• Wildfire activity: Roughly 1.8 million acres had burned nationally by late April — nearly double the 10-year average — including the historic Moral Fire (Nebraska) and Ranger Road Fire (Oklahoma/Kansas). The Climate Prediction Center's flash-drought outlook signals continued rapid drying risk in the West.
• Canada: The same blocking ridge is forecast (per CanSIPS and Copernicus) to deliver anomalous May heat and dryness across British Columbia and Alberta as Pacific storms continue to be deflected northward into a Gulf-of-Alaska/Aleutian storm corridor.
• Agriculture: The USDA forecasts the lowest U.S. wheat acreage since 1919 amid widespread drought; 88% of Nebraska, ~60% of Colorado and Utah, and nearly 82% of Florida are in extreme or exceptional drought (the last largely a separate Southeast story, but symptomatic of the broader pattern).

Notably, the eastern half of the country has experienced the inverse — cooler than normal temperatures and frequent moisture — including beneficial precipitation that reduced drought in parts of the Southern Plains and Southeast in early May. This dipole, warm/dry West and cool/wet East, has been the signature pattern of the past two winters and the spring of 2026.

Connection to Broader Climate Patterns

ENSO state: NOAA's CPC declared the end of the 2025–26 La Niña in April 2026 (the "Final La Niña Advisory") and issued an "El Niño Watch." The May 2026 ENSO probability update shows ENSO-neutral conditions transitioning rapidly toward El Niño, with El Niño favored for May–July 2026 (NOAA ≈ 61–62%; the IRI April plume placed the chance at 70% for AMJ and 88–94% thereafter through DJF 2026/27). NOAA gives El Niño a 96% chance of persisting through DJF 2026–27. The WMO has flagged "high confidence" in El Niño onset by mid-2026, with the spring predictability barrier the principal remaining uncertainty. The late stages of a La Niña — and the residual cold-pool/atmospheric inertia that lingers after one — are classically associated with a strengthened, northward-displaced NPH that suppresses storminess along the U.S. West Coast while keeping the polar jet active to its north, which is consistent with what has been observed. (USDA meteorologist Brad Rippey notes that the developing strong El Niño may provide some relief later, particularly to the southern tier in winter 2026–27, but this is far from certain and there is a huge water deficit to make up.)

Jet stream and blocking: The split-jet configuration with a near-vanishing 250-hPa flow over the ridge core represents textbook high-amplitude blocking, occasionally forming Omega-block geometries. Peer-reviewed work on a projected increase of summer "heat-dome-like" stationary waves over northwestern North America (npj Climate and Atmospheric Science, 2023), together with analyses by Deirdre Des Jardins and Daniel Swain, argue that the leading mode of North American winter circulation has shifted toward a recurrent warm-West/cool-East dipole (sometimes called the North American Winter Dipole or NAWD), linked to greenhouse-gas-forced changes in the jet stream and the atmospheric waveguide. There is also published evidence (Bartusek et al. 2022; others) that low Barents Sea ice can preferentially favor ridge-building over western North America via Rossby wave responses.

Climate-change linkage: Multiple lines of evidence connect the NPH's recent behavior to anthropogenic forcing. Hadley-cell expansion has been observed at roughly 0.1°–0.5° latitude per decade over the past ~40 years, with consequent poleward migration and intensification of subtropical highs (Grise and Davis 2020; Schmidt and Grise 2019). CMIP6-based projections show 21st-century poleward shifts of subtropical highs of order 1.5°, with the subtropical jet strengthening in winter. Modeling by Schmidt et al. suggests North American summertime precipitation is more sensitive to shifts in the subtropical highs than to changes in the zonal-mean Hadley cell — even modest poleward and onshore expansion of the NPH can have outsized drying effects on the western U.S. While the central pressure of the NPH itself may weaken slightly in some warming projections (the CESM Large Ensemble shows reduced central-Pacific subsidence and a northward shift of the descent maximum), the impact on landfalling moisture remains drying for the U.S. West Coast.

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2. The Azores / North Atlantic Subtropical High and Northwest Africa

Current Position and Behavior

The Azores High (also called the North Atlantic Subtropical High; in its summer western-displaced form, the Bermuda High) in mid-May 2026 is in the early phase of its seasonal poleward and westward migration. Climatologically, the system's center moves toward roughly 35°N over the eastern Atlantic and Iberian Peninsula during late spring, then toward Bermuda (with central pressure typically around 1024 hPa) by midsummer.

The system's behavior over the past eight months has been unusual in two phases:

1. Winter 2025–26 — anomalously displaced/weakened over the eastern Atlantic. The High sat farther east, or was less expansive, than typical for recent decades, which allowed an exceptionally active Atlantic storm track to penetrate south into Morocco and Algeria. Successive frontal systems and atmospheric rivers brought rainfall and high-elevation snow that, by January 12, 2026, prompted Morocco's water minister to formally declare an end to a seven-year drought — the worst in 40 years. National dam fill rates rose from 28% (January 2025) to 46% (January 2026); winter rainfall was 95% higher year-on-year and 17% above the seasonal average; snowpack briefly covered 55,495 km² of mountainous terrain. By February 20, 2026, Copernicus satellite imagery showed water resources up roughly 155% versus the prior year in northeastern Morocco, with several reservoirs overflowing. Heavy rains, however, also triggered destructive floods and landslides — a familiar "whiplash" pattern.
2. Spring 2026 transition — High reasserting subsidence. By April–May 2026, the Azores High has begun reasserting its more conventional configuration, with subsidence redeveloping over the northwestern Sahara and the eastern subtropical Atlantic and the Sahara Heat Low (SHL) intensifying inland. NOAA CPC's Africa Hazards Outlook in May 2026 flags "much above-average temperatures" likely to produce "abnormally hot conditions in southern Mauritania" and adjacent regions — consistent with strengthening subsidence on the southern flank of the subtropical ridge. Real-time visualizations on earth.nullschool.net show the characteristic anticyclonic gyre re-establishing itself between roughly 25–40°N over the eastern Atlantic, with northeasterly trade winds reasserting along the African coast.

How the High Affects Moisture Flow Around Northwest Africa

The Azores High shapes northwestern African moisture in three principal ways:

• Direct subsidence and aridity. The system is the surface expression of the descending branch of the Northern Hemisphere Hadley cell. Its sinking air aloft produces dry adiabatic warming and stable stratification that maintain the Sahara's hyper-aridity and the Mediterranean Basin's summer drought. When the ridge is strong and expansive, this subsidence reaches farther into Morocco, Algeria, and the Iberian Peninsula.
• Steering of Atlantic frontal systems. The High's location dictates whether mid-latitude cyclones traversing the North Atlantic dip south into Morocco (when the ridge is contracted or displaced east, as occurred in 2025–26) or are deflected north of Iberia toward the British Isles and Scandinavia (when the ridge expands poleward, as it tends to do in summer and increasingly does year-round under anthropogenic forcing — see below). Britannica notes that periodic offshore high-pressure ridges shifting storms northward are a primary cause of Moroccan drought episodes. The cold Canary Current along Morocco's western coast adds another layer of low-level stability that further suppresses precipitation.
• Steering of African Easterly Waves and Saharan dust. On the southern flank of the high, anticyclonic clockwise circulation generates the northeasterly trades and the Harmattan, which carry African Easterly Waves and Saharan dust westward across the tropical Atlantic toward the Caribbean. The latitude of the Azores High is more strongly correlated with winter Saharan dust transport than the NAO index itself (Riemer et al. 2006 and follow-ups).

Implications for the Sahara Margin and the Sahel

Even as the Azores High shuts down Atlantic moisture incursions to its south, the seasonal northward migration of the Intertropical Convergence Zone (ITCZ) is starting to deliver the West African Monsoon (WAM) to the southern Sahel. The 2026 PRESASS / AGRHYMET regional seasonal outlook, presented in N'Djamena ahead of the rainy season, warns of uneven rainfall: some areas likely to see above-average rains and elevated flood risk, others delayed or below-average rains with heightened drought and food-security concerns. Government and humanitarian agencies have been urged to undertake early water-management and disaster-risk preparation.

This bifurcated outlook is consistent with the Sahel's well-documented increasing rainfall variability. Yang et al. (Nature Communications, 2026) find that greenhouse warming is projected to increase Sahel interannual rainfall variability, raising the frequency of both extreme wet and extreme dry seasons, particularly in the central-eastern Sahel, with stronger ENSO variability part of the driver. About 70–90% of West African annual precipitation is delivered by Mesoscale Convective Systems (MCSs) embedded in the WAM; the position and strength of the SHL and the African Easterly Jet (AEJ) determine where these MCSs concentrate, and both are sensitive to the subtropical Atlantic high above them.

Northwestern Africa proper (Morocco, western Algeria, Mauritania) is sandwiched between two regimes the subtropical Atlantic High mediates: a Mediterranean cool-season rainfall regime to the north (which delivered this past winter's drought-busting rains) and the WAM zone to the south, with the Sahara core in between dominated by year-round subsidence. With the Azores High now expanding back toward its summer configuration, Morocco is entering its long dry season; the question for coming months is whether the High will lock into the expanded position typical of recent decades, in which case the wet winter will represent only a temporary respite from structural drying.

Connection to Broader Climate Patterns

Climate change and Azores High expansion. The landmark paper by Cresswell-Clay et al. (Nature Geoscience, 2022) — using observations, ensemble climate-model simulations, and proxy records from Portuguese stalagmites — found that winters with an extremely large Azores High have become significantly more common in the industrial era (post-1850) than at any time in the past 1,200 years. Specifically, the frequency of extreme-large-Azores-High winters has increased from roughly one every 10 years in the pre-industrial period to one every four years in the 21st century, with an extreme event reducing rainfall on the western coast of the Iberian Peninsula by about 35.3 mm per month. The authors attribute the expansion to anthropogenic greenhouse-gas forcing.

A caveat noted in commentary on this paper: Jacob Scheff (UNC Charlotte) has pointed out that the paper's "unprecedented in 1,200 years" claim strictly applies to the CESM Last Millennium Ensemble in most simulations; high-resolution real-world verification across a full millennium is not directly possible. Nonetheless, the observational expansion since 1850 is robust, and complementary work indicates a northward migration of the Atlantic-high center of roughly 0.25° latitude per decade (p < 0.02), consistent with the projected poleward expansion of the Hadley cell.

Broader Hadley-cell context. The Atlantic case is one regional expression of the global poleward shift of subtropical highs linked to Hadley-cell widening. CMIP6 projections for the MENA region show subtropical highs migrating poleward by ~1.5° by the end of the century under SSP5-8.5, with the subtropical jet strengthening by about 10% in winter and storm tracks shifting poleward. Modeling indicates a further westward expansion of the high toward the southeastern U.S. and a 35% intensification of coastal upwelling along northern Iberia by 2070–2099 under SSP5-8.5 — both of which would amplify drying over southern Europe, the western Mediterranean, and the northern Maghreb. Spanish researchers have characterized this trend as a "subtropicalization" of the Iberian climate, with a weakening of the zonal jet and an increase in both extreme dry and extreme wet (convective) events.

ENSO. Unlike the Pacific case, the Azores High's seasonal behavior is less directly entrained by ENSO; the North Atlantic Oscillation (the high's pairing with the Icelandic Low) is the dominant mode of variability. However, ENSO transitions like the current La Niña→El Niño shift can modulate tropical-Atlantic SSTs and indirectly influence the high's strength and position, particularly during late summer and autumn, and ENSO is one driver of Yang et al.'s projected Sahel variability increase.

The 2025–26 anomaly in context. The very wet 2025–26 Moroccan winter therefore appears to have been a notable interannual departure from the recent expanding-Azores-High trend — a reminder that internal NAO variability still produces large excursions from the long-term forced trend. Whether this represents a one-off respite or the beginning of a less-expanded regime cannot yet be determined; published projections continue to indicate a long-term drying trajectory for the western Mediterranean and adjacent North Africa even as interannual variability rises.

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3. Synthesis: Two Hemispheres, One Mechanism

The two systems described here — the North Pacific High redirecting Pacific moisture away from western North America, and the Azores/North Atlantic Subtropical High strengthening over the eastern Atlantic to suppress moisture flow into northwestern Africa — are not unrelated. Both are manifestations of the Northern Hemisphere subtropical ridge, the surface expression of the descending branch of the Hadley circulation. Both have been shown, by independent lines of evidence, to be expanding poleward, intensifying, and producing more frequent extreme blocking episodes in the industrial era, with peer-reviewed attribution to anthropogenic forcing in both cases.

The mid-May 2026 snapshot captures this in real time:

• The NPH is anchoring a winter-into-spring blocking pattern that has already produced one of the most anomalous heat events ever observed in the cool-season American West (March 2026) and has driven U.S. drought coverage to near-2012 record levels just as El Niño begins to develop. Pacific moisture is being routed into a Gulf-of-Alaska/Aleutian storm corridor to the north and into a subtropical jet across northern Mexico to the south, with the western interior bone-dry beneath persistent subsidence.
• The Azores High, after an anomalously displaced winter that broke Morocco's seven-year drought, is reasserting its climatological grip on northwestern Africa as the West African Monsoon begins to engage to the south — with regional climate centers warning of both flood and drought risks across the Sahel and the structural drying trend across the western Mediterranean remaining intact.

A developing El Niño, superimposed on the warmest-on-record western U.S. winter and a still-recovering Moroccan water system, sets the stage for a 2026 in which atmospheric blocking continues to be a dominant story.

4. Uncertainties and Caveats

• Real-time central-pressure values for the NPH and Azores High on May 14–15, 2026 were not located as discrete numerical readings in publicly indexed sources beyond NOAA OPC text products. Qualitative characterizations (strong, persistent, northward-displaced NPH ridge; Azores High beginning seasonal expansion) are firmly supported by NOAA OPC analyses, NOAA CPC Africa Hazards Outlook, ensemble depictions, and analyst commentary. earth.nullschool.net visualizations qualitatively confirm both patterns (an expansive subtropical-Pacific anticyclone with a northward ridge axis to the West Coast; a re-strengthening eastern-Atlantic ridge) but do not produce a citable instantaneous central-pressure figure.
• Long-lead ENSO forecasts cross the spring predictability barrier; even the strong model consensus on El Niño development through 2026 carries genuine uncertainty, and forecast outcomes range from continued ENSO-neutral to a possible very strong El Niño (NOAA puts the chance of Niño-3.4 ≥ +2.0 °C in winter at roughly 1 in 4).
• Climate-change attribution for individual events (e.g., the March 2026 heat dome) is well-established by World Weather Attribution and Climate Central. Attribution of the pattern — the recurring NAWD-style warm-West/cool-East dipole and the expanded Azores High — rests on convergent but still-active research programs, with some critiques (e.g., Scheff's on Cresswell-Clay et al.) noting limits on what individual model studies can prove about pre-instrumental real-world variability.
• The Azores High's wet-winter 2025–26 anomaly over Morocco illustrates that the long-term trend toward greater subtropical high expansion does not preclude large interannual departures. One wet winter has not resolved Morocco's structural water-resource problem; the government continues a major investment in desalination (targeted at ~60% of national drinking water by 2030).
• Source quality. Some pattern interpretations draw on respected analyst blogs (Weather West, California Water Research) and forecast-summary sites (Pogodnik, drought.gov, weatherbug) that are distinct from peer-reviewed literature; they have been used here for synoptic context, with primary peer-reviewed studies (Cresswell-Clay et al. 2022, Yang et al. 2026, Schmidt and Grise 2019, Hadley-cell expansion literature, and the September 2023 npj Climate and Atmospheric Science work on heat-dome-like stationary waves) used for the structural climate-change claims. Some forward-looking statements in forecast outlooks use conditional language ("may," "could," "is expected to") and are treated here as outlooks rather than established facts.

Overall, mid-May 2026 represents an unusually clear illustration of how the Northern Hemisphere's two great subtropical anticyclones — long-known features of the climate system — are increasingly behaving in ways that amplify regional drying on their eastern and equatorward flanks, while occasionally allowing extreme storm windows (such as Morocco's drought-busting winter or eastern-U.S. severe weather) to slip through. The atmospheric blocking the user's query describes is real, it is current, and it is increasingly understood as a manifestation of a circulation regime now being reshaped by human-caused climate change.