S.W.I; BC; Smooth

Radio Record, Volume VI, Issue 1, 15 July 1932, Page 3

S.W.I; BC; Smooth

The Weather Report and Forecast

by

Dr.

S.

Kidson

-from 2YA-

HE weather is a very . variable quantity, and every day there are quite a lot of facts about it, each of which some persons are anxious to know. The majority of these people would be best pleased if we were just to write-a chatty little note telling them exactly what they want to know and no more, ut the requirements of different people are so varied that it would take a long time to cater to them all, and during most of that time the majority would be bored by details in which they were not interested. It is not possible for them to switch in only when the little bit they are ‘interested in is coming through. Besides which, weather forecasting has not reached such a pitch of accuracy that the meteorologist, even at the best of times, can say exactly what is going to happen at all places. : _ In order to get the report into reasonable com- , pass, then, we have to make use of a certain number of technical terms and forecast only the ‘general features of the weather. When it comes to giving the weather at the various ports, a kind of shorthand has to be used. Even so, although ships’ officers are urging

us to include additional stations, city dwellers have lost patience by the time the five minutes devoted to the weather is up, and are dying to get back to their jazz. They, therefore, clamour for the station reports to be cut out. The quickest way in which to convey an understanding of the

situation to anyone with a knowledge of meteorology is to give him as much as is readily possible of the information which the meteorologist himself has received, and then to give the meteorologist deductions from it. And nowadays, it must be remembered, practically all ships’ officers have a working knowledge of meteorology, al! aviators should have it, and most children are beginning to get it. OST farmers have some , idea of it, because the ( weather affects them so _ vitally. The* report begins, therefore, with a brief description of the general situation. The best guide to the latter is the distribution of air pressure in all the surrounding regions. Air pressure is what the barometer measures. I have previously compared the variation of pressure from place to place with the variation in contour of a land sur- ~~ face. A region of high pressure may be compared to a hill and one of low pressure to a valley, or a basin, according to its shape. The meteorologist calls the pressure hill or area of high pressure an anti-cyclone, and

the low-pressure area a depression. Generally there is more or less of a ridge of high pressure extending from Southern Australia across to the north of New Zealand. Along this ridge, generally at a distance from each other of about 2000) miles, are larger elevations or anti-cyclones. Between two anti-cyclones is a saddle which leads on the south side to a pressure valley or depression. Sometimes the valley has several branches, or the first depression is followed by secondary depressions. | Now, the important thing to remember is that each of these pressure features has a characteristic system of wind and weather with it, and that they are practically always moving from west to east. AN RES near the centre . of an anti-cyclone the weather is generally fine and winds light. As the anti-cyclone begins to move away eastward and the depression between it and the next anticyclone advances, the barometer falls and the wind commences to blow from the north-west, and the steeper the slope of pressure toward the depres-; sion, the stronger the wind will be. The sky soon clouds over and rain sets in. Usually it is

confined to districts with a westerly aspect, that 1s, those which meet the north-west winds directly. When the barometer has reached its lowest there is a sudden change of the wind to south-west, the temperature falls, and the barometer usually starts to rise rapidly. The heaviest rains are near the

trough-line ot the depression or the DOttOH! of the pressure valley, as we may term it. The southerly winds bring most of the rain which falls in eastern districts and the nearer they are to south and the further from west, the better are the chances of rain in these districts. After a while, the next anti-cyclone begins to approach. The wind drops and the weather improves. Occasionally, instead of the usual valley of low pressure opening to the south, which is our ordinary westerly depression, a cyclone may forin in or wander into our neighbourhood. The cyclone is an area of low pressure of approximately circular form, with high-pressure all round. It may be likened to a basin in the mountains. Now, the rain is generally widespread and heavy round a cyclone, and since the winds usually blow from the north-east as it approaches, and from the south-east while it is passing, it brings its worst weather to the east coast. It is often, too, accompanied by fog. The descriptions I have given are necessary very brief and general in character, As a matter of fact, no two depressions are quite alike. And the winds experienced during the passing (Continued on page 24.)

LHE DAILY REPORT

| Abbreviations --R, Rough; 8S. Smooth; C, Consider- | able; M.S. Moderate Swell; M. Moderate. | . aes

The Weather Report

(Continued from page 3.) of a cyclone depend on whether the centre passes to the north or south of the place concerned.. Nevertheless, I hope my remarks will help you to understand the sort of weather to expect when you hear that there is a cyclone centred over the Tasman Sea or an -anti-cyclone over South-Hastern Australia. The winds do not call for much comment, but in applying it to your own district, you must remember the effect of local features, such as hills, on particular winds. A wind which is westerly at most places, for example, will be northerly at Wellington. Next comes the forecast for seas in New Zealand waters. The only thing to remember here is that when we say "rough south of Hast Cape" we mean only on the east coast south of East Cape. North of Farewell Spit will mean on the west coast north of Farewell Spit, and so on. ; We then give the weather in the eastern half of the Tasman Sea. We leave the western half to the Austrapan authorities who know more about t. The last part of the forecast concerns the weather to be expected during the coming 24 hours. In the 7 p.m. report from 2Y¥A are given, in addition to the foregoing, reports of the weather at 4 p.m. from 13 ports in New Zealand, from Chatham and Norfolk Islands, and from Sydney and Hobart. To anyone with a knowledge of meteorology this part of the report conveys a great amount of: information.

It will tell him much about the prevailing depressions and anti-cyclones that it was impossible to include in the first part of the report. He will know the reason for the forecast, what the alternatives are and how the forecast may be upset. If he is a ship’s captain it may be very important for him to know the weather at his destination. If his ship is a large one, the work at loading or unloading he will be able to do after arrival will depend on the weather. He can adjust his speed economically to suit the wind. If his ship is a small one bound for an exposed port. he may know that it will be a waste of coal to try to get there, and so forth. The reports also enable anyone to draw their own weather charts. Many merchant vessels and all naval vessels ~ this.

The station reports give first of all the barometer reading in inches at the place concerned at 4 p.m. The reading is given to hundredths of an inch. Next comes the temperature in degrees Fahrenheit. Next in is the direction from which the wind was blowing, followed by the force on the Beaufort seale. The different numbers on the Beaufort scale are defined as follow :- Calm-0: Calm; smoke rises vertical-ly-0 (equivalent speed in miles per hour at 33ft.). Light air-1: Direction of wind shown by smoke drift, but not by wind vanes-2. Slight breeze-2: Wind felt on face; leaves rustle; ordinary vane moved by wind-5. Gentle breeze-3: Leaves and smal] twigs in constant motion; wind extends light flag-16.

Moderate breeze-4: Raises dust and loose paper; small branches are moved -15. Fresh -breeze-5: Small trees in leaf begin to sway; crested wavelets form on inland waters-21. Strong breeze-6: Large branches in motion; whistling heard in telegraph

wires; umbrellas used with difficulty27. High wind-7 : Whole trees in motion; inconvenience felt when walking against wind-~ab. Gale-8: Breaks . twigs . off trees: generally impedes progress-42. °

Strong gale-9: Slight structural damage occurs (chimmney-pots. and slates removed )-50. Whole gale-10: Seldom experienced inland; trees uprooted; considerable stractural damage occurs-59. Storm-11: Very rarely experienced ; accompanied by widespread damage68 é Hurricane-12: Above 75. | A report of a wind as N.W. 5, therefore, means that a fresh breeze was blowing from the north-west, and so on. We next come to the weather, which is indicated by the letters of the Beuufort notation, as follows :- b-Blue sky, cloudless. be-A combination of blue sky w ith detached clouds. e-Sky mainly cloudy, but with openings between the clouds. o-Completely overcast. g-Gloom. ~ u--Ugly, threatening appearance. r-Continuous rain. \ d--Drizzle. s-Snow. p-Passing showers, bh-Hail. q-Squalls. 1-Lightning. ; t-Thunder. f-Fog. m-Mist. z-Dust haze, The last word gives the state of the sea. Bven if you are not meteorologists, you will be able ‘to tell from these reports if there is rain about, or how far up the coast a southerly change has reached, or whether the trip to Lyttelton is to’ be a ‘rough one, _

Station. Cape Maria vau Diemen Auckland _ Bast Cape .... Cape Egmont . Farewell Spit Wellington Cape Campbell Greymouth . .. Akaroa Lighthouse Puysegur Pt. Chatham Is. . Sydney cose Hobart wove Barometer, Inches 2957 2952 2959 2960 2973 2968 292 "B76 2975 2983 2976 8015 oR ky & po STIS QW H Weather.