'Once-in-decades' Super Typhoon Neoguri makes an early impact on Japan
Meteorologist/Science Writer
Tuesday, July 8, 2014, 5:46 PM - As Super Typhoon Neoguri sweeps past Okinawa and heads towards landfall in southern Japan today, news sources such as The Guardian, and JapanToday.com have quoted a Miyako fisherman who, in speaking to NHK television, said: "It's rare that we brace for a typhoon (as early as) July." So, what's behind Neoguri's early and powerful appearance?
Neoguri (Korean for 'raccoon') spun up over warm tropical Pacific Ocean waters east of the Philippines, starting on June 30. Within days it had advanced not only in strength - becoming a Tropical Depression and then a full-fledged Tropical Storm by July 4 - but it had also advanced to the west, tracking over even more warm ocean water as it veered northward, towards Japan. By end of the day on Friday, July 4, forecasters with the Joint Typhoon Warning Center (JTWC) had upgraded Neoguri to Typhoon status, and as it was still out over open water, it continued to intensify, becoming a Super Typhoon on July 6. It has weakened since then, after passing by the island of Okinawa and moving over the East China Sea, and it is expected to continue to weaken before it makes landfall on the island of Kyushu, and then tracks along the east coast of Japan, past Tokyo and off to the north by Sunday.
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With all tropical cyclones - tropical storms, hurricanes, typhoons, etc - their strength depends on two main factors: 1) how much warm ocean water they have access to as their energy source (specifically water above 27 C, which extends down to a depth of at least 50 metres or so), and 2) how strong the winds are at the top of the storm compared to those at the bottom of the storm (ie: the wind shear).
The basic 'engine' of a hurricane is fairly simple. Warm water evaporates from the ocean surface and is taken up by the air just above the water, increasing the humidity and warming that air as well. In turn, that warmed, moist air rises up, cooling as it does, and releasing energy as the water it picked up evaporates, forming clouds and rain. When the now-cooled and dry air reaches the top of the storm, it is cycled back downwards in the core of the storm and at its edges, where it warms up, gathers more moisture, is sucked back into the storm clouds and the process repeats. The warmer the water, the more energy that can be passed on into the storm, the faster the whole process goes, and the stronger the storm can grow. However, for this 'engine' to run most efficiently, the circulation of air inside the storm has to be as straight up-and-down is it can. If the orientation of the eye and clouds is tilted in any way, such as when the wind speeds get stronger as you go higher up in the storm (ie: strong wind shear), this slows and limits all the processes of releasing and gathering energy in the storm. It can't grow as powerful and if the shear is strong enough, it might tear apart the storm before it can develop.
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The fisherman from Miyako is right about Neoguri. While it's not unheard of to have a typhoon this early, as they can (and do) happen at any time of the year, it is a little unusual for Japan to see one make landfall in early July. According to the Japan Meteorological Agency, the country sees most of their typhoon landfalls in August, and they list ten tropical cyclones over the past 60 years or so as making landfall in Japan earlier than normal. The latest of those was in late June (2004), s Neoguri isn't too far off from making that top-ten list. Forecasters had already been expecting an above-average Pacific Typhoon Season, roughly the opposite of predictions for the Atlantic Hurricane Season, and a big reason for both of these forecasts was the expected development of an El Niño - the 'warm phase' of the El Nino Southern Oscillation (ENSO) - in the equatorial Pacific Ocean.
NEXT PAGE: How El Niño affects storms, and could it be responsible for Neoguri's early arrival?
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.