Small-scale effects like water temperature and wind shear have a big effect on storm formation and strength, but large weather patterns, like El Niño, influence them as well. Normally, under 'neutral ENSO' or La Niña conditions, there's a strong, steady wind blowing west across the equatorial Pacific Ocean, which flows upwards over southeast Asia and then back towards South America high up, forming one big 'conveyor belt' of air flow over the Pacific. At the base of this circulation, friction from the wind drags the surface waters along, so that they 'pile up' in the west. If you were to look at a cross-section of the ocean during this time, the water surface would slanted, higher (and warmer) in the west and lower (and cooler) in the east. Every few years or so, though, this big circulation breaks down into several smaller circulations, and with the force of friction weaker, the water 'sloshes back' towards the east. The overall effect of all that heat changing positions is that weather patterns all around the world shift and are displaced, and this has different effects on tropical cyclone formation for different parts of the world.

In the Atlantic Ocean, sea surface temperatures are certainly warm enough to fuel storms right now, as we just saw with Hurricane Arthur over the past week. However, El Niño is notorious for causing the winds high up over the tropical Atlantic Ocean to flow faster than normal, without causing a similar increase for winds at the water surface. This increases wind shear, which, as it says above, tends to tilt storms and weaken them.

However, El Niño has the opposite effect on wind shear over the tropical Pacific Ocean. With less wind shear, storms maintain the vertical orientation they need to keep their 'engine' running smoothly, so it's easier for them to form and grow stronger. Also, since the warmer ocean waters that are normally mostly confined to the west spread back towards the east during El Niño, the storms can form earlier than they usually do, and further to the east, which gives them a longer track of warm water to pass over before they make landfall.

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So, with these well-known connections between El Niño and typhoon development, is the one that's supposedly developing in the Pacific now responsible for Neoguri's early development, and thus for it taking aim on Japan? Some precedent has been set, since of those top ten 'earliest typhoons' to hit Japan, eight of them did occur during a year when there was at least a weak El Niño either in the works or fully-developed. That is by no means conclusive evidence, but it does show an interesting trend, and researchers have been noting links between El Niño and typhoon timing/strength for several years now.

However, it's difficult to answer that question at the moment. We're definitely not in a fully-developed El Nino yet, and there's still a lot of uncertainty about whether it's really happening this year. However, El Niño doesn't suddenly develop all at once. If it did, the resulting tsunami that would be directed at the west coast of South America would be catastrophic, and the chaos unleashed into the atmosphere would likely be devastating too. It takes months for all the factors to slowly coalesce, as oceanic and atmospheric patterns gradually shift around. Right now, even though the World Meteorological Organization (WMO) is saying that "sea surface temperatures are above average across virtually the entire tropical Pacific, not just in the eastern and central portions," those central and eastern parts are showing more warming than the rest (compared to last year and the overall average). That's exactly the sea-surface temperature pattern we expect to see for a developing El Niño, and it's sea surface temperatures that are most important for tropical cyclone development, especially since the atmosphere over the Pacific has normal wind shear.

So, if, later this year, we look back to what was going on now, and we see that it was all just a slightly more complicated development of an El Niño, we'lll probably be safe to put Neoguri in the list of storms that were (at least) influenced by this weather pattern. However, if we're looking back on this in December and an El Niño has not developed by then, something else will be behind Neoguri - simple natural variability perhaps, or possibly even climate change as it warms our oceans and could be causing the tropics to expand farther from the equator. Either way, we'll have to wait until later this year to find out.