Three tropical cyclones are expected to flank the equator in the western Pacific by late this week — two in the Southern Hemisphere and one in the Northern Hemisphere. Twin tropical cyclones forming on either side of the equator typically happen once or twice a year, but seeing triplets is quite unusual. In this case, one (Tropical Cyclone Maila) is already at Category 2 strength and is unusually close to the equator, raising the risk of colossal rains and flooding in some places that seldom or never see tropical cyclones.
The other Southern Hemisphere storm, located well to the southeast of Maila — Cyclone Vaianu — is also a Cat 2 and is predicted to peak as a major Cat 3 storm by Tuesday. And in the Northern Hemisphere, a large tropical disturbance (Invest 90W) located to the north of Maila is predicted to become Tropical Storm Sinlaku by late this week, potentially threatening Guam and the Northern Mariana Islands this weekend, according to Monday morning forecasts from the GFS and European (ECMWF) models.
These three cyclones will provide an extra nudge for what’s already one of the strongest embryonic set-ups for El Niño that some longtime researchers have ever observed. The El Niño and La Niña patterns in the tropical Pacific influence weather across the world.
Cyclone Maila a rare threat to Papua New Guinea
Over the weekend, Cyclone Maila became the first hurricane-strength storm on record in the heart of the Solomon Sea north of 10°S, according to NOAA’s Historical Hurricane Tracks database. As of 11 a.m. EDT Monday, Maila had intensified to just below Category 3 strength, with top sustained winds of 110 mph (180 km/h).
Despite Maila’s slow and erratic motion — a mode that tends to upwell cooler water from below and inhibit intensification — the storm is taking advantage of otherwise favorable conditions for development: warm sea surface temperatures of 28-29 degrees Celsius (82-84°F), deep warm water with a high oceanic heat content (100-150 kilojoules per square centimeter), moderate wind shear, and strong upper-level outflow.
Maila will spend another day or two lingering over the central Solomon Sea as its circulation spawns round after round of heavy rain. These could affect parts of the Solomon Islands, but the heaviest amounts may end up in the remote, sparsely populated islands of eastern Papua New Guinea. Some islands could be deluged by rainfall totals in the 20-to-40-inch range, and even higher local amounts can’t be ruled out.
By late week, Maila is projected by the Joint Typhoon Warning Center to pass over or near the southeastern tip of mainland Papua New Guinea, perhaps still packing Category 1-level winds. By next weekend or thereabouts, it could reach northern Queensland, Australia. A landfall on Papua New Guinea would be rare if not unprecedented; more often, powerful cyclones will pass south of the mainland and intensify en route to Australia. One example is Cyclone Ita (2014), which rapidly intensified after passing Papua New Guinea, peaking at Cat 5 strength. In 2007, Cyclone Guba moved slowly through the Coral Sea, never making landfall but briefly reaching Cat 3 strength and dumping torrential rains in Papua New Guinea, leading to at least 200 flood-related deaths.
Well southeast of Maila, Cyclone Vaianu was just below Category 3 strength, with top sustained winds of 110 mph (180 km/h), at 11 a.m. EDT Monday. Vaianu is on a straightforward south-southeastward track that should deliver few if any major impacts to land areas, although its remnants could bring several inches of rain to northern New Zealand in about a week.
Tropical cyclones can help drive an El Niño to develop
The counter-clockwise circulation of 90W in the Northern Hemisphere and clockwise circulation of Maila in the Southern Hemisphere (and to a lesser extent, Vainanu in the Southern Hemisphere) are feeding into and benefiting from a pulse of westerly surface winds near the equator that are running counter to the usual east-to-west trade winds. A series of so-called westerly wind bursts over the western equatorial Pacific over the past month has been pushing warm water eastward. The subsurface equatorial Pacific is now warmer than average for April, with only a paper-thin layer of cooler-than-average waters at the surface. These are portentous signs of what may become a truly powerful El Niño event by later this year.
One of the world’s top atmospheric models goes hyper-bullish on El Niño
April is often too soon to gain a confident sense of whether El Niño, La Niña, or neutral conditions will be in place for the next northern fall and winter. This year, though, the tropical Pacific seems intent on punching right through the notorious “spring predictability barrier” of the El Niño/Southern Oscillation, or ENSO.
On March 12, NOAA issued an El Niño Watch and gave a better-than-even chance that El Niño will be in place by midsummer. And now some of the world’s leading seasonal forecast models are upping the ante. In the just-released April ENSO outlook from the European Center for Medium-range Weather Forecasts, every one of the 20-plus model ensemble members is predicting moderate or strong El Niño conditions by mid-June, barely two months from now.
For October, roughly half of the ECMWF ensemble is calling for sea surface temperatures in the main El Niño region (Niño3.4) to exceed 2.5 degrees Celsius above the seasonal average. Such values would correspond to what’s loosely referred to as a “super El Niño.” Though there’s no official definition for a “super” event, the term is often attached to El Niño when its peak anomalies reach at least +2.0°C. Since 1950, the only El Niño events that have hit this threshold for at least one three-month interval were in 1972–73, 1982–83, 1997–98, 2015–16, and 2023–24. Only one of those events, in 2015–16, pushed all the way past +2.5°C.
A model collection known as the North American Multi-Model Ensemble hasn’t released its April ENSO forecasts yet. However, nearly all of its ensemble members from the March forecast were predicting sea surface temperatures consistent with El Niño to be in place by June. A few members were pushing El Niño anomalies past +2.0 degrees Celsius by October. (It’s hard to know exactly how far they went, since some of the output literally went off the high end of the scale, as shown in Fig. 4 below)
A similar model ensemble, this one gleaned from European research centers and maintained by the Copernicus Climate Change Service, also shows high consistency in its ensemble forecasts from March 1.
On April 9, NOAA will be issuing its next monthly ENSO diagnostic discussion, which will include the agency’s latest official month-by-month probabilities for El Niño as well as a probabilistic outlook for El Niño strength. It wouldn’t be a shock to see a jump in the current odds of 33% that El Niño conditions will end up reaching the “strong” level (in other words, an anomaly in the Niño3.4 region greater than +1.5 degrees Celsius).
One caveat to keep in mind: Although the latest ECMWF forecast is higher than others in part because it’s drawing on more recent data, there are also a couple of technical factors that may be giving its values a slight boost:
- The ECMWF forecast is calculated against a 1981-2010 baseline rather than the warmer 1991-2020 baseline. This earlier baseline would tend to artificially raise the forecast anomalies.
- The ECMWF forecast doesn’t incorporate the adjustments for tropics-wide warming that are folded into NOAA’s new Relative Oceanic Niño Index (RONI). Here too, the net effect of this absence would likely be an overestimate of El Niño strength – perhaps by at least 0.5 degree Celsius, according to climate scientist and communicator Tom Di Liberto.
The colossal influence of ENSO, and why spring is a tough season for predicting it
ENSO is the single biggest shaper of year-to-year weather over much of the planet. Although an El Niño event benefits some regional economies, the long-term global cost can be massive – perhaps as high as $4.1 and $5.7 trillion for the super 1982-83 and 1997-98 events, according to one 2023 analysis. (That’s far larger than some earlier estimates, and scientists differ on how to make such calculations.)
By northern summer, it’s often fairly clear how ENSO will unfold for the following few months. That’s hugely valuable for seasonal forecasting: It allows farmers, water managers, and other specialists to plan ahead, knowing where and when the odds of unusually wet, dry, warm, or cold conditions are likely to be boosted.
These vital outlooks have long been hobbled by the spring predictability barrier. ENSO phases typically wind down in northern spring and reemerge by summer or fall, so it can be tough for models and forecasters to identify exactly when those switches will get flipped. Moreover, the last several decades have seen several noteworthy “false alarms,” wherein a potential El Niño taking shape in April fizzled by later in the year. All this adds up to ENSO forecast skill that’s historically been weakest in the first few months of the calendar year – though newer dynamical models are increasingly more capable than older statistical models at successfully overcoming the spring predictability barrier.
That said, the barrier may get undercut this year by the sheer potency of the preconditions already in place for what could be a super El Niño event. As pointed out by Paul Roundy, an ENSO expert at the University at Albany, SUNY, the anomalous westerly winds over the western tropical Pacific are currently exerting even more force than those during spring 1997, during the embryonic stages of the super El Niño of 1997-98 (the one invoked by the late Chris Farley in a brief but legendary “Saturday Night Live” sketch).
According to Roundy, there is “real potential for the strongest El Niño event in 140 years.”
New research suggests that the largest El Niño episodes can reset the global climate for decades afterward. A paper published in Nature last December, led by Aoyun Xue of the University of California, Los Angeles, looked at long-term regime shifts in surface air temperature, soil moisture, and sea surface temperature. Especially in those places where El Niño already has a big influence, the study found that super El Niño events “exert a far stronger and more spatially extensive influence on [climate regime shifts]” compared to weaker events: “Despite the cyclical nature of ENSO, super El Niño events can trigger persistent climate shifts that reorganize regional baselines. Through nonlinear amplification and memory mechanisms – such as oceanic heat storage and land-atmosphere feedback – these events generate sustained anomalies that outlast the El Niño phase itself.”
How soon could an El Niño event help quench the fast-growing U.S. drought?
El Niño tends to enhance cool-season precipitation throughout the U.S. Sunbelt. That could be a much-needed salve for areas dessicated by the recent incredible March heat wave, which arrived on top of a drier-than-usual winter in many areas, especially the U.S. Southwest.
The problem is that most of the seasonal effects in North America from a building El Niño or La Niña event don’t kick in till after summer. This is largely because the atmospheric reverberations from ENSO’s home base in the eastern tropical Pacific are more powerful when they play off against the stronger jet stream that sets up in fall and winter. Nevertheless, seasonal forecast models are projecting above-average rainfall this summer across much of the Central and Northern Plains and Midwest (see the embedded post below).
The North American Monsoon could be a more immediate source of moisture for the Southwest. Driven by the intense heating of late spring over the region’s deserts, the monsoon typically pulls moisture northward across Mexico in May and into Southern California and the Four Corners states by July and August, often spawning intense lightning storms, heavy localized rains, and flash floods. There’s great year-to-year variability in the monsoon, though, so it’s too soon to know how strong it might be and how it might intersect with any influence from an early-arriving El Niño event. But with record-warm ocean temperatures off the coast of Baja Mexico from March’s incredible heat wave, this summer favors heavier downpours than usual.
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