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Yeongam,Ìý22 -Ìý24ÌýOctober 2010 (Round 17)

(This forecast will be regularly updated. This entry: FridayÌý22 October, 18:40hrs BST)

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ÌýForecast Summary:

(PPN = Precipitation)

Emphasis:ÌýHigh confidence for dry Friday; Saturday's FP3/Quali sessions alsoÌýexpected to remain dry. Improving inter-model continuityÌýsuggests aÌýthreat of rain arriving into Sunday, with increasing potential to affect the race.

Friday:ÌýCONFIDENCE HIGH: Sunny spells and dry. Chance of PPN 5%. Max 22C.Ìý Breezy at times. Wind ENE.

Saturday: CONFIDENCE HIGH: Turning cloudier during the day. Rather breezy again. Expected to remain dry throughoutÌýFP3/Quali.ÌýÌýChance of PPN 30% until end of quali,Ìýbut rain arriving late evening / towards midnight. Max 21C. WindÌýENE.

Sunday:ÌýCONFIDENCE MODERATE (improving): Mostly cloudy. Rain expected to have arrived overnight, albeit heaviest PPN expectedÌýfurther to theÌýsouth. Possible that wet weather will have departed before race start, but this remains open to a high degree of uncertainty. Chance of PPN 70%. ÌýMax 19C. Breezy.Ìý Wind ENE.Ìý

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Synopsis & Forecast Evolution:

Update to original entry (below):

Friday Update, based on 12z Model runs:

There's closer agreement generally now between the main operational centres, with a high chance of rain falling across the circuit at some stage later Saturday and into Sunday. This has been strongly signalled for some timeÌýin the ECMWF-ENS output for Mokpo; ditto (with good continuity) by Canada's GM, the UKMO-GM, Japan's GM and (on and off) by NOGAPS. Korea's own KMA modelling and meteogram spreadÌýoffers a similar idea.

The US-GFS has tended to play catch-up of late, now bringing rain overnight Saturday and into Sunday morning, but clears it well ahead of race start. This solution has about 50% support and we'll see if the 00zÌýGFS (and other op centres)Ìýbuild on the theme of dry weather and / or onlyÌýlight showery outbreaks of rainÌýprevailing by the time the lights go out. Certainly not impossible, in my view.Ìý The Canadian model falls into a roughly similar camp, with fairly heavy overnight and morning rain trending much lighter ahead of race start.

Meanwhile, the Japanese, EC and UKMO modelling still threaten outbreaks of rain (some heavy)Ìýcontinuing into the race window. The Canadian output had alsoÌýdoggedly stuck to this idea virtually all week, with UKMO not far behind in terms of continuity and remaining so in the latest run. ECMWF's output is best summarised in a remark from the Met Office's Deputy Chief Forecaster made to me earlier today, who - afterÌýanalysing the Mokpo EP meteogram -Ìýconcluded: "....(there's) clearly a high chance for some heavy rain, either before the race, if not actually during it."

So it's a very finely balanced situation; further runs are needed to gauge continuity on the areal spread of heaviest rainfall and the timing of any clearance off eastwards.ÌýBroadly speaking, a middle ground approach is to anticipate rain arriving overnight and into the morning (= green track), mostly clearing away to the east before midday but with potential for some lighter showery outbreaks continuing for a while into the afternoon.

Thursday Update, based on 12z Model runs:

Today's ensembles maintain a trend - already offered with high forecast confidence some days agoÌý- for dry running to prevailÌýthroughout Friday's sessions and a strong prospect of the same outcome on Saturday. The focus of forecast attention remains very much fixed onÌýSunday, with a growing prospect of rain arriving during the day, courtesy of the ex-Megi remnants described in the original entry (below). As also highlighted below, this threat of wet weather has been consistently offered by some models as a minority to 50% solution, while the US-GFS - suffering some earlier upstream divergence in handling Megi's track - has continued to oscillate in solutions for Sunday.

Crucially however, it has tended toÌýerratically edgeÌýthe prospect of rain northwards in successive recent runs. It's 12zÌýoutput now comes into broader, if not exact,Ìýagreement with most other operational centres (ECMWF, UKMO, JMA, CMC, NOGAPSÌýetc.)Ìýby bringing a prospect of rain across the extreme SW and S districts of South Korea throughout Sunday. Other models are more bullish, with a more northerly, extensiveÌýthreat of rainÌýand in the case of CMC (exhibiting strong continuity), offering showersÌýpotentially slightly earlier from overnight Sat-Sun. The timing of this - plus precise degree of northerly extent of anyÌýprecipitation -Ìýwill be the critical factors during race day.Ìý

Clearly, tomorrow's runs will be important in terms of continuity (or lack thereof); CMC, UKMO and some others having already 'led the way' in threatening a wet or potentially wet race, with GFS tending to play catch-up in the last 24hrs. I'll update you all again tomorrow, by which time we'll have seen just how the teams fare on the new circuit in dry, fine conditions during FP1 and 2!

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(Original Entry follows)

While the Suzuka forecastÌýwas a (rare) example of great inter-model continuity andÌýbullish forecast confidence -Ìýeven quite a few days ahead of the event - assessing weather prospects at this inaugural Korean eventÌýhave beenÌýproving quite the opposite!

Forecast confidence is now starting to improve and consolidate. Currently, only the weather for Friday's practice sessions can be foretold with a very high degree of certainty:Ìýit's looking dry, fine and rather breezy for those. The various models are starting to show increasing agreement for the rest of the track action to stay dry, too.

Now, I hope you can keep up with this next bit - but it's pretty critical in determining just how dry (or not) the new and doubtless rather slick asphalt will remain by the end of the race weekend!

The complications emerge especially during Sunday, much of them courtesy of how extra-tropical remnants from Typhoon 15W, named 'Megi', track and evolve through the mid to latter parts of next week.

Right now, Megi - located SE of Hong Kong - is tracking very much as anticipated, steeredÌýaroundÌýthe southern boundary ofÌýa deep-layeredÌýmid-level subtropical ridge. WithÌýtime, the western portion ofÌýthat ridge of high pressure will subside due to mid-latitude influences coming east out of China, while the typhoon itselfÌýis expectedÌýto continue it's more poleward track.

Megi isÌýcurrently expected to make landfall into S.E. China / Hong Kong, according to the official model output from the .Ìý Therafter however, the complex evolution of the dissipating core - and extent and distribution of it's northward rainfall outflow - are all influenced by various factors, including a trough emergingÌýsouth-eastward through mid-central China. However, it will certainly dissipate and weaken as the poleward journey continues during the week,Ìýthrough theÌýincreasing influence of land and decreasing potency of vertical wind shear. But the northerly-orientatedÌýoutflow of rainfall and associated 'lobes' of low pressure will remain pretty noteworthy features on weather chartsÌýfor a few days still, some of this possibly crossing - or at least grazing -South Korea later during the race weekend. However, this is most likely to occur post-race andÌý overnight int Monday.

The main 'free' forecast model output available on the web, feeding many automated popular forecast websites, is the US-GFS model. Importantly, it has persisted in offering a divergent track in certain respects compared to the collective (and very similar)Ìýoutput of other dynamic models (e.g., ECMWF, UKMO, NOGAPS, GFDN). On the basis of consensual expert analysis, the GFS trackÌýyou might see on some weather websites is still presently considered the 'outlier' solution by the Joint TyphoonÌýWarning Center and is, in their words, "....deemed as unlikely,Ìýconsidering the strength and positionÌýof the steering subtropical ridge positioned to the north."Ìý

Consequently, the GFS forecast further 'downstream' into later stages of next week may prove somewhat unreliable for south Korea (at leastÌýat this range), albeit continuity in the broaderÌýweekend prospectsÌýfor Mokpo is now improving.

The UK Met Office and Canadian CMC modelsÌýwere both quite progressive in taking a threat of rain - some heavy - northward towards Korea into the weekend. Previous runs of UKMO suggested overnight wet weather Sat-Sun but unlikely to directly impact track sessions; CMC, meanwhile, offered a decidedly wet race.ÌýUKMO has now reverted to a dry solution for Saturday and Sunday, bringing the threat of rain only later during Sunday and into Monday. CMC, however, sticks to the notion of a very wet spell into and throughoutÌýthe race window. It remains effectively alone in this very pessimistic solution (but that doesn't mean it's to be discounted!).

GFS has exhibited some pretty typical oscillations at this sort of forecast range and especially in a complex set-up.ÌýÌýIt sticks to the idea of dry weather all weekend, steering any rainfall southwards across Japan.ÌýECMWF, meanwhile, is essentially the closest to the Megi 'official' track published by the Joint Typhoon Warning CenterÌýand also looks to keep the race weekend dry or largely so.

A reasoned summary, for now at least, suggests:

- dry, sunny & breezyÌýweather all of Friday;

- very probably dryÌý(and again breezy, plus eventually somewhat cloudier)Ìýconditions for Saturday's sessions, and

- a dry, breezy and fairly warm race the more likely outcome, but with an uncertain, lowÌý%Ìýthreat of rain appearing during the event.

I'll of course keep you updated all the way...