April 2018 – Penny Tranter “Sailing Weather”

Penny Tranter has had 35 years working at the Met office, and is a sailor. So she understands as we do the importance of weather to sailors, but, unlike most of us, can read and interpret the clouds, satellite pictures, weather data, weather maps and so on to explain what is going on and what might happen next. The Met office is one of the top two weather forecasters in the world – the other being another island beside a big ocean, which we failed to guess. It’s Japan.

I am not sure it was a talk, exactly – it had a fairly strong lesson flavour – but that made a refreshing change. It was amazing just how much ground Penny managed to cover, explaining inter alia basic principles of the effects of pressure differences, how and why air rises and falls, and how the jet streams meander at the intersections of the polar, tropical and equatorial “cells” of our Northern hemisphere.

Portrait photo of Penny Tranter for Sailing Today.

In the UK we come under the influence of air masses coming in from the SW (Tropical maritime), S (Tropical continental), E (Polar continental), NW (Polar maritime) and N (Arctic maritime). The Azores High tends to dominate, generating our prevailing S’Westerlies; that recent “Beast from the East” was an example of a strong easterly, bringing us Siberian weather.

Clouds have much to tell us. Ten defined types with Latin-derived names in three groups (disappointingly not named in Latin but just as Low, Medium and High). The high clouds are ice particles, not water. (Held up how, asked one of us? Answer: they are fine crystals not lumps so no need to worry.) And of course there are many bits of doggerel for us sailors to mutter, as we touch the side of our nose, knowingly, such as “Mare’s tails and mackerel scales make tall ships carry low sails”.

We were shown weather maps aplenty. Fronts and occluded fronts abounded. Strong winds go with the steep pressure gradients of tightly packed isobars, light ones where isobars are far between. At one point we were all stood up, with a hand outstretched, to illustrate Buys Ballot’s law: in the Northern Hemisphere, where the wind circulation is counterclockwise around low pressure and clockwise around high pressure, a person standing with their back to the wind has the lower air pressure to the left. (Reminded me of Fleming’s motor/generator rule – but with that you hold up the thumb and two fingers of one hand to show relative directions of motion, current and magnetic field. Honest).

A little excursion was made into coastal weather, where air warmed by sunned land has to rise, drawing in air from above the cooler and more temperature stable sea. If the coast is convex or concave there are “focussing” effects.

Penny was asked which of the various sources of weather forecasts we use she rated – the answer being that different sources seem to be better in different places.

I think we passed muster, just, in our responses to the questions Penny occasionally threw at us. Questions like: what’s the difference between weather and climate? And if that’s the cloud formation you’re seeing, what direction is the wind coming from?

Oh – and we should not feel sorry for Michael Fish – he’s dined out on his famous gaffe for years. And is the climate changing? Yes, says Penny – we are getting more extremes than we used to. No doubt a bout it.

A great evening. A bit less laughter than on some occasions, but enriching!