After years in the making, we are just two days out from surfing's first dance with the Olympics. And, will you be watching on Saturday when the waiting period begins? There's been much 'ooohhh' and some 'ahhh', at the thought of Shidashita, aka the Olympic venue, even getting waves for the event. But there's a jolly ol' Typhoon in the mix for the forecast, with another system breaking off that thing's eastern flank that could make things...tricky.
UPDATE: Sunday July 25 11am: The storm that formed in the wake of Typhoon In-Fa, now officially Tropical Storm Nepartak, is currently about 600 miles east-southeast of Tokyo, moving steadily towards the northwest, with winds of around 45 kts, and expected to reach the coast of Japan by Tuesday. The fetch on its northern flank has already started generating surf for the contest area.
Tomorrow, Monday, the centre of the system moves towards the coast and the fetch to the north continues to generate swell, with some discrepancy between the models as to the exact trajectory. The fetch could either end up directly northeast of the contest site, or further north with the major part of the fetch out of the swell window. Therefore, there is still some uncertainty in the swell size from late Monday onwards. Whatever happens, there is now a high probability of surfable waves until the end of the contest period.
The exact trajectory of the storm and the intensity of the wind on its western flank will also affect local conditions on Monday. Most models agree that winds will be from a northerly quarter, but they could either be light to moderate or up to strong or even gale force.
On Tuesday, the system moves north of the contest area, which means local winds will be lighter and begin to back around to an easterly quarter. Again, the exact direction and strength depends on where the storm ends up.
UPDATE: Friday July 23 11am: Typhoon In-Fa is currently just passing over the Yaeyama and Miyako Islands, moving slowly towards the northwest with winds of around 90 kts, and producing some heavy conditions in northern Taiwan. It is expected to weaken slightly before making landfall near the city of Ningbo in China, early Sunday.
The tropical cyclone to the east in the wake of In-Fa has started to develop, and is currently about 800 miles southeast of Japan, with an area of southeast winds on its northeast flank. Winds are currently estimated to be around 25 kts, but expected to strengthen within the next 24 hrs. This system, which has now been acknowledged by the Joint Typhoon Warning Centre (JTWC) as ‘WTPN21’ is what will produce surf for the contest area. Some swell is already being generated, which will arrive at the coast during Sunday.
By Saturday, the fetch is expected to move slightly north, expand and strengthen, with reasonable agreement between models, although some are showing stronger winds than others. The increased windspeed, longer fetch and the persistence of the windfield over the same stretch of ocean, means that more swell will arrive at the contest site by Monday. At the moment, the GFS model – upon which most of the wave forecasts are based – is suggesting a weaker windfield than the other models, which means that wave forecasts for Monday could be an underestimation.
We'll keep you updated as this thing moves on.
EARLIER: Thursday July 22. Yes, the world's best surfers have touched down in Japan for the 2020 Tokyo Olympic Games. And while it seems half the surfing population is waiting with baited breath and the other a certain degree of nonchalance, you can't help but feel a certain anticipation around it all, no?
Waffle. On to the forecast. “Typhoon In-fa is currently just east of the Yaeyama Islands, moving slowly westwards with maximum sustained winds of around 110 kts,” says MSW forecaster Tony Butt.
“Over the next 24 hrs it will turn towards the northwest and accelerate, passing north of Taiwan by Saturday before making landfall in mainland China, just south of Shanghai, by Sunday.
“However, it is not Typhoon In-Fa itself that could generate some large surf for the contest site. It is a second system that develops southeast of Japan and moves north around the eastern periphery of In-Fa. This system, associated with a trough of low pressure in the wake of the Typhoon, begins to deepen later today, Thursday. Stable areas of high pressure to the north and east mean an intense pressure gradient generating an area of strong winds from an easterly quarter, which in turn could send some large swell towards Japan.
“Current atmospheric forecasts for Friday show and area of strong southeast winds about 800 miles east-southeast of Japan. There is fairly good agreement between the models, although the GFS model (upon which most of the wave forecasts are based) shows considerably stronger winds. Whatever the case, this fetch should produce a pulse of swell which arrives at the contest side sometime during Sunday.
“On Saturday [aka opening day!] the fetch intensifies and expands towards the northeast, again with fairly good agreement between the models, although the GFS continues to suggest stronger winds than the other models. This should at least keep the swell pumping through Monday, with the possibility of a larger, longer-period pulse if that windfield does intensify.
“Sunday is when the models really start to diverge, with some suggesting that the fetch will remain in the same place and continue pumping swell into the contest area, while others suggesting that the system quickly moves towards northern Japan, out of firing range. This means a much greater uncertainty in local wave heights after Monday.
“Current spot forecasts for the contest site show around three to five feet for Sunday, with fresh northeast (onshore) winds. The MSW probability factor for Sunday is up to 70 per cent, which means there is still some margin for error, but at least there will be some surfable waves.
“On Monday, probabilities are down to below 30 per cent due to the uncertainty around the windspeed in the fetch on Saturday. However, even if the fetch turns out to be the weakest out of all the models, there will still be something around three feet or so on Monday, with improved wind conditions.
“After Monday, probabilities are even lower, so please stay tuned for updates as the model predictions gradually converge.”