There is a substantial inverse correlation between tropical Pacific Sea Surface Temperatures (SSTs) and tropical Atlantic activity, which directly modulates conditions in the Atlantic Main Development Region (MDR). This interbasin connection is primarily driven by the El Niño-Southern Oscillation (ENSO) cycle via atmospheric teleconnections.
1. The ENSO Teleconnection Mechanism:
The relationship is not driven by a direct mixing of water, but rather by changes in the global atmospheric circulation (specifically the Walker Circulation) triggered by Pacific SST anomalies.
When Pacific SSTs are Warm (El Niño):
When the central and eastern equatorial Pacific experiences anomalously warm SSTs (+ENSO), it triggers intense atmospheric convection over the Pacific.
Increased vertical wind sheer:
This shifts the upper-level wind patterns, sending strong westerly winds across the Caribbean and into the tropical Atlantic MDR. These strong winds clash with the low-level easterly trade winds, creating high vertical wind shear. High shear literally rips developing tropical disturbances apart.
Atmospheric Stability:
El Niño induces broad anomalous sinking motion (subsidence) and warmer upper-tropospheric temperatures over the Atlantic basin, which stabilizes the atmosphere and suppresses deep convection.
MDR Response:
Even if local Atlantic MDR waters are warm, an active El Niño act as a powerful "brake" on hurricane development.
When Pacific SSTs are cool:
Cool (La Niña) Conversely, when Pacific SSTs are below average (-ENSO), the opposite occurs.
Reduced Vertical Wind Shear:
Convection shifts to the far western Pacific, causing the upper-level westerlies over the Atlantic to weaken. Increased Instability: The atmosphere over the MDR becomes much more unstable, with enhanced rising motion and deep tropical moisture pushed into the region. MDR Response: This creates an environment highly conducive to tropical genesis and intensification.
2. The "Relative SST" Concept
In modern climate science, researchers look closely at Relative SSTs—the temperature of the Atlantic MDR relative to the rest of the global tropical oceans.
If the tropical Pacific warms faster or is warmer than the Atlantic, the global tropical troposphere warms, raising the thermodynamic threshold required for convection in the Atlantic. Therefore, even if the MDR is technically warmer than its historical average, it may underperform if the Pacific is significantly warmer. Conversely, if the Pacific cools (La Niña) while the Atlantic MDR remains exceptionally warm, the two factors work in tandem to create hyper-conducive conditions for extreme development.
Current conditions.
Right now, we are seeing a fascinating, textbook setup of this exact interbasin relationship playing out in real time. The ocean-atmosphere setup has changed dramatically over the last few months, shifting the outlook for the hurricane season.
Here is exactly how the anomalies look across both basins as of June 2026:
1. The Tropical Pacific: A Rapidly Intensifying El Niño
The tropical Pacific is undergoing a confident warming trend. NOAA and the Met Office officially declared the start of an El Niño event, and it is ramping up incredibly fast, we spotted this back in April when subsurface temperatures were romping eastward. The Core Anomalies: In the central equatorial Pacific (the critical Niño 3.4 region), weekly SST anomalies have surged to +1.7^\circ\text{C}.
Subsurface Heat:
Beneath the surface (at depths of 50–150 meters), a massive reservoir of warm water is packed into the central-eastern Pacific, with localized anomalies hitting up to +6^\circ\text{C}. This acts as a massive engine room, guaranteeing that this El Niño will continue to intensify through the summer and autumn.
Atmospheric Response:
The atmosphere has fully coupled with the ocean. The Southern Oscillation Index (SOI) is strongly negative (sitting at -21.9), and the easterly trade winds have severely weakened or even flipped to westerlies.
Current climate models are highly aligned, predicting this will peak as a strong to very strong El Niño later this year, potentially ranking among the most intense events observed since 1950.
2. The Atlantic MDR: Robust Anomalous Cooling
While global sea surface temperatures as a whole remain exceptionally warm, the tropical Atlantic Main Development Region (MDR) is presenting a very stark contrast to the record-breaking warmth seen over the last couple of years.
The Local Anomalies:
The eastern and central tropical Atlantic MDR have actually experienced significant anomalous cooling, dropping below average for this time of year. Only the far western tropical Atlantic (near the Caribbean) is holding onto near-average temperatures.
The "Relative SST" Trap: Because the Pacific is warming at a near-historic pace while the central/eastern Atlantic MDR has cooled below climatological norms, the Relative SST values for the Atlantic are deeply negative.
3. The Real-World Impact on the Seasonal Outlook
Because the anomalies have lined up this way, major meteorological institutions (like Colorado State University) have notably reduced their 2026 seasonal hurricane forecasts to below-normal levels.
Normally, a warm global ocean provides plenty of background thermal energy, but the combination of a potent, rapidly growing Pacific El Niño and cooler-than-normal local MDR waters is expected to unleash exceptionally high vertical wind shear straight across the Caribbean and tropical Atlantic. This atmospheric "shear wall" is anticipated to act as a major suppressor, keeping a lid on deep tropical organization and storm track development through the peak of the season.
Written by David I Birch
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