Mostly dry and bright on Saturday with light winds. Dry for much of Sunday, but rain expected overnight as winds strengthen. Cloudy on Monday, with rain at times. Gales expected later. Very windy on Tuesday, with squally showers and W'ly gales.

The remainder of next week unsettled and windy. Turning cooler, as strong winds veer NW'ly.

GENERAL SITUATION AND SYNOPSIS 06:00 UTC
A moist SE'ly airflow will strengthen today, as a small low centre - swinging past northwest Scotland - drives fronts across Shetland. A SW'ly airflow will follow later this evening, as the depression continues past Shetland towards Iceland.

During Saturday, a small frontal disturbance is expected to run east across mainland Scotland, effectively maintaining a relatively slack airflow over the Northern Isles. On Sunday, we will see the high over Scandinavia easing away into Russia, while another in the Atlantic ridges northeast close to southern Britain. As a result, the SE'ly airflow of the last week will be replaced by one from a SW to W'ly direction.

This will strengthen on Monday, as a developing wavelow runs rapidly northeast. By Tuesday, this is expected to be a very deep and vigorous feature to the north of Shetland.

This depression is presently predicted to move into Scandinavia, with a very strong SW to W'ly airflow veering NW'ly as it does so.

[From an analysis of my Fair Isle climate records, the third week in September is the period when the first major gale of the autumn makes its appearance.]

FORECAST FOR NEXT THREE DAYS
Confidence level: Weather type - medium. Timing - medium.
Temperatures ranging from a daytime high of 14° to 16° Celsius down to an overnight low of about 10° Celsius.

FRIDAY 10th: A misty start with low cloud and fog, this rather extensive across Shetland at first. However, it will tend to lift - more especially in the north and west, where there will be some sunshine - but it will be slow to clear from the Fair Isle and Sumburgh area. Rain will reach Orkney during the morning, this extending across Fair Isle soon after midday, and reaching Shetland during the afternoon. Orkney will become drier and brighter again later in the afternoon. The rain, perhaps heavy for a time, will clear Shetland later this evening. Light F3 SE'ly winds, increasing F5-6 in the rain, will veer F5 SW'ly with the arrival of the brighter conditions. Mainly dry tonight with clear spells. F5 SW'ly winds at first, but easing and backing light S to SE'ly.
Sea state - Overnight becoming mainly slight, with a 1 metre S'ly wind-swell. Steadily increasing rough, with a 3 to 4 metre wind-swell by the afternoon, this SE'ly in direction at first, but becoming SW'ly by evening.

SATURDAY 11th: Bright with sunny spells and just the chance of one or two light showers, these most likely across Orkney during the morning. Winds F2-3 at first and generally S'ly in direction, but later veering SW'ly and increasing F5, as more frequent showers spread in from the southwest towards evening.
Sea state - Overnight becoming moderate or rough, with a 2 to 3 metre SW'ly wind-swell in western waters and around Shetland. Moderate with a 2 metre S'ly wind-swell east of Orkney.

SUNDAY 12th: Sunny spells and showers. F4-5 SW'ly winds increasing F5-6 by evening, ahead of rain spreading from the southwest overnight.
Sea state - Overnight becoming moderate or rough, with a 2 to 3 metre W'ly wind-swell.

10-DAY OUTLOOK
Confidence level: Weather type - medium. Timing - medium/low.
Temperatures in the daily range 13° to 15° Celsius down to about 10° Celsius. Probably a degree or so cooler later.

MONDAY 13th: Mostly cloudy, with rain at times. Strong SW'ly winds later backing S or SE'ly and increasing strong to gale, with rain turning heavier overnight.
Sea state - Moderate to rough becoming rough, with a 2 to 3 metre SW'ly wind-swell increasing 3 to 4 metres S'ly.

TUESDAY 14th: Rain clearing to squally showers, as strong to gale S'ly winds veer W'ly and increase gale or severe gale-force.

WEDNESDAY 15th - MONDAY 20th: Blustery showers and turning cooler, as winds veer NW'ly. Strong to gale at first, winds may ease by the weekend. Showers becoming less frequent.

Be aware that the weather over north-west Europe - and especially around the Northern Isles - is part of an ever-changing and dynamic system. Therefore regard the '10-Day Outlook' as a guide only - there are times when any outlook going beyond about 36 to 48 hours is likely to prove unreliable.

Always check the latest forecast from the UK Met Office before undertaking any weather-dependent activity.
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