THE WEATHER

Nelson Evening Mail, 16 September 1916, Page 4

THE WEATHER

DOMINION METEOROLOGIST IN NELSON AN INTERESTING INTERVIEW. Mr D. C. Bates, Dominion Meteorologist, spent to-day in Nelson inspecting the Meteorological" station and making the necessary arrangements consequent on the departure of Ma- A. E> Hedges, who is now in camp. Speaking to a Mail representative this morning, Mr Bates stated that as its climalte, -which is the sum total of the weather, was one of Nelson's greatest assets, intelligent interest should, be taken in it by all residents and especially by those in authority. Mr Bates further stated that there was considerable scope for useful worki for Nelson in this direction. Some people, said Mr Bates., think Dliat the weather forecasting is the principal part of the work, of the .Meteorologist Department, tout this is not so. The main energies are centred in climatology and accurate details of the weather in all parts of the Dominion are carefully recorded d'ay :by day and: year 'by year. In (Nelson at the present time the Rev. J. R. Dart is recording the rainfall and! temperatures and 'Captain 'Collins the sunshine. WEATHER MAPS. For some little time past The Mail has been publishing daily -weather maps, and Mr Bates kindly consented to explain their meaning for (the information of the public. Ke stated: —"The weather maps •display in small compass the chief conditions affecting the weather. Every morning at 9 o'clock the curtain is lifted as it were in different parts\ of NewZealand and we get a momentary glimpse of donditions all over the Dominion. Reports are telegraphed into the Bureau, and the -winds, etc., are plotted- on a chart, and tflien the most important element so far as the forecaster is concerned is the varying) weight of the atmosphere as shown iby the readings of the' ■barometer in various parts. Knowing these, lines of equal pressure are drawn over the chart. Tihese lines are called tfs'olbars {equal pressures) and it has been well said what a hairpin is to a woman that the isobar is to the meteorologist. Be uses them to put <up his forecast of wind and seas and tides. Weather maps vary from day to day, but types have -been chosen and such are used iby the Mail to portray the general conditions on which the forecast is hased and at the samte time to give a bird's eye view, of wind and pressures of all who are interested l in such- matters.

WEATHER TYPES. ' 'AM weather types group themselves into three kinds—i(l) First the cydlone or circular disturbance with closed isobars. This is a system which usually finds its way from tropical or sub-tropical regions and chieftyi affects tihe North- Island, especially in winter.

"In the above map iti will be. seen that the isobar passing through Wellington also touches Tauranga, Cape 'Campbell, and Kumara. We have no station .there,, but Hiokitika will' igrve a reading as.much above the isobar as Greymoutih. is; below. The isobar passing through Gape Egmonfc and FareweE Spit; will ibe The isobar off East Cape and cutting ■Oamaru will be higher than either. SEOOiM) .TYPE. :J'\! ■ "The second type is tihe -westerly low. or Antarctic disturbance that travels ironind the, world: along' the 'Roaring Forties.' "this "type of storm chiefly af•feots the weather i,h and; south of "Cook Strait. It is the most usual distebance and sometimes envelops all the dominion.

"Here tlhe lowest reading is at the BhxS, and df the barometer then reads 29.1 the next isobar cutting 'Oamanui will Ibe 29.2 audi Dmnedin. will probably report a ibarometri'o pressure of, 29.16. Cbristcburch line is 29.2 ; Cape Campbell and Farewell 1 .Spit 29.4; Napier ■- and Kawhia 29.5; East Cape, Tiritiri and HoManga 29.6, while 29.7 lies northward •towards the Three Kings. These lines extend ovei* the ocean, and ocean forecasts, which are sent out every night from Wellington, Awanui, in the far nortih and AwaruaJ in the south are 'bared on their projection'. "The'third 1 type is the anti-cyclone or' ■high pressure system most frequently associated with sunny days and cool nights.

".Here the barometer b high, everywhere, 'but' -usually lie readings are a, little lower /.in the extreme North and) South. "The first tiling to note about these systems is the wind arrows showing the direction from which the wind comes. The winds flow 'along almost parallel to; the isdbars around the centres of the various systems —clockwise around! the low pressures and! counter-clockwise in. the (high. This, in the cyclonic type above (T) the centre of low pressure, is ■westward of the North Island and northwesterly windis prevail in t<he far North and S.S. in Otago, while N l . winds are reported off Napier. "In the second or westerly type the windis will dhange from N. by W- to S. during the passage of the storm. "Iu the third; type the winds move counter-clockwise or 'lback' around the centre of high pressure 'here depicted as at Nelson. Calms and light and variable winds accompany such a distribution, ibut strong easterlies often occur about Auckland! at the same time as. fresh westerlies are reportedl in Foveaux Strait. "Another thing to l>e remembered is the fact that disturbances have a forward; path from <wesfc to east, as well as a rotary motion of their own about their own oentres. The 'following map shows two westerly lows, one passed eastward and another coming on. This was the position ait the end of last week, according to the map. published, in our columns on 'Saturday last.