40 Transactions. — Miscellaneous. 



Art. IV. — On the Principle of New Zealand Weather Forecast. 

 By Commander K. A. Edwin, E.N. 



Plates I-III. 

 [Read before the Wellington Philosophical Society, l\th October, 1879.] 

 The subject treated of in this paper is one wliich has for some years past 

 received great attention in other countries, and their publications upon 

 Weather Forecast give us ample information as to the method by which 

 their predictions are arrived at, and the measure of success which has 

 attended their efforts. It is now proposed to give some description of the 

 manner in which the Weather Forecast of this colony is carried out. The 

 subject IS one which may be considered of general interest, and the- method 

 of procedure differs in some respects from that practised in other coun- 

 tries ; but as it has ah'eady stood the test of some remarkably changeable 

 seasons, with a large percentage of success, it seems now desirable to invite 

 further investigation in the matter. 



In the first efforts to arrive at some conclusions as to probable changes 

 in the weather, the principal difficulty which came under consideration was 

 the deflections which the mountainous nature of the country seemed to have 

 power to create, not only in the direction of the wind, but also in the dis- 

 tribution of pressure. For instance, an isobar will generally run very fairly 

 from Eussell to Grahamstown, Tauranga, Gisborne, and Napier ; but 

 instead of continuing toward Castlepoint and Lyttelton, it will be found to 

 curve inland and westward toward New Plymouth, then to turn southward 

 between the latter place and Wanganui, and return eastwards towards Castle- 

 point which it leaves on its right. Now, it will be found upon investiga- 

 tion that pressure is nearly always higher at Westport and Hokitika than at 

 Kaikoura, which necessitates this isobar being again drawn westward, i.e. , back 

 through Cook Strait, and passing Cape Farewell turn toward south to West- 

 port and Hokitika, from which point it returns eastward, passing out be- 

 tween Blenheim and Kaikoura. A second isobar should have commenced 

 at Auckland and run toward Taupo, Wanganui and Blenheim ; and a third 

 might be reasonably expected to pass over Westport, Hokitika, Queenstown, 

 and Balclutha ; but it is evident that, according to meteorological law, they 

 must follow the first line of equal pressure upon that side which will show 

 that they define the position of a lower pressure, and this necessitates their 

 following it through all its sinuosities, but westward of it. 



Such distributions of pressure were found to be by far the most preva- 

 lent state of affairs, and in many instances the curves were much more dis- 

 torted than shown on the diagram (PI. I., fig. 1 j, but it seemed probable 

 that other disturbing influences must also be in existence, and tending to 



