Weather

The Island Climate
Denis J Simmons

MARITIME INFLUENCE Though not so maritime as the Isles of Scilly, the Hebrides or Shetland, which are more remote from the mainland, and perhaps more importantly, from the Continent, the Isle of Wight, a mere 147 square miles in area, is nevertheless under the influence of the sea at all seasons.

Winds off the English Channel naturally keep the day temperatures lower in summer on all windward coasts and a little higher in winter compared to inland Britain at a similar altitude. Mean maxima in the warmest month, usually July or August, range from 19° C at St Catherine’s Point to 21.5 °C at Newport. Mean night temperatures are higher at the coast at all seasons , and there are fewer air frosts in the winter half year with, typically 22 at Ryde and 32 at Newport. Over the year the mean minima at St Catherine’s Point is 8.1° C while Newport averages 7.3° C. The latter is in an "inland valley" situation, giving our capital town a slightly more continental climate, with warmer days and colder nights.

RAINFALL varies from around 710mm on the south-west and West coasts to about 900mm in the Shanklin and Newport areas, due to orographic enhancement caused by the downs to the South-west. The proportion of the annual fall in the summer half year (April-September) is roughly 40% of the total. In unsettled weather, we often escape showers in the summer half year, provided the wind blows off the channel; often, the sky is clear to the South and East, while heavy clouds producing showers and thunderstorms occur over the mainland. In the winter half year, October to March, the reverse applies as the sea, rather than the sun, is the warming agent. With north-westerly winds we expect a clear sunny day in winter, while North and West facing coasts of mainland Britain have showers, probably of a wintry nature (hail or snow).

SUNSHINE The Island has long boasted its sunshine records. The coast from Sandown to Ventnor in particular enjoys as much sun as the Sussex resorts, next only to Jersey which has the highest recorded figure for the British Isles (1941 hours annually, 5.3 hours daily over the year).

Daily averages range from 2 hours in December to as much as 8.7 hours at Shanklin in June (1947/1970). The average for the three resorts (Sandown, Shanklin, Ventnor) is 1860 hours annually (5.1 hours daily). Inland Hampshire has an average of approximately 1500‑1550 hours annually (4.1 ‑ 4.2 hours daily).

WIND Whilst not experiencing on a regular basis the fierce Atlantic storms of North-west Ireland and Scotland, we can, on occasions get a "good blow" mainly from the South-west or West during the winter half year. Obviously the "Back of the Wight" between St Catherine’s Point and Freshwater get the full force of such winds. Rarely, the Needles and St Catherine’s have recorded gusts of 100 mph or slightly above, for example, October 16, 1987, when a hurricane struck south-east England.

SNOW Large amounts of snow have occurred from time to time, most notably in January 1881 when 3 metre drifts were formed in a violent Easterly gale, but such extremes are a rare occurrence. In recent years heavy snowfalls have been absent (global warming?). Snow or sleet, however slight, occurred on average only 6 days annually during the 1990/1999 period and was lying on an average of only 1 day at 0900 hours at Newport; a 32 year average 1969/2000 inclusive, works out at 8 days of snowfall and 3 days with snow lying at 0900 hours respectively.

FOG Advection fog (when warm, moist air is cooled by contact with a cold land or sea surface) is not frequent, occurring on around 7 days at 0900 hours at Newport on average, and around 20 days at all waking hours each year. Sea fog tends to affect the coast to a greater extent than inland in the early Spring and Summer months, when a warm moist airstream passes over the still chilly sea; they are usually not frequent, but seen from time to time most years between March and June.

STORMS We normally have heavy frontal storms imported from the continent, often arriving in the late evening, rather than the local variety, which are more common in the London area and East Anglia on summer afternoons. At other times, particularly in the late autumn, the comparative warmth of the sun sets off storms when the upper air is cold. These storms affect the island and other south coast areas, while places inland tend to escape. From records taken over 60 years at Totland Bay, the observer, Mr John Dover, stated that his area rarely has overhead thunderstorms. He attributed this to the downs coming to a point at the Needles to the south-west diverting the storms from the South and West, sending them up the Solent or English Channel.