|
The prospect was for the core of the
sub-tropical anticyclone to reign supreme and generally restrict convective
cloud development. There was also the outside consideration though that, being
more on the edge of this zone of descending air; some alto-level inflow of
tropical air could appear. Interestingly, the one aspect faltered and the other
became more prominent. Considering the overall dryness of the air,
we did not do too badly.From Saturday onwards,
isolated convective development has been visible both by sight and by satellite
observation. Rainfall reports are certainly scant and, where recorded, have
shown the limited precipitation activity
Although there has been some alto-level
moisture, there is no input of surface moisture. The advent of our rainy season
still lies ahead.
We should remember though, that at this
time of the Southern Hemisphere season, the oceans, pressure patterns and
resultant wind-flows would all be favoured by the emerging La Nina conditions.
Around the southern oceans, the eastern
anticyclonic cells are tracking close to the 40oS latitude and
showing values above the 1030 hPa mark.
f some interest, though, the breaking up
of the warm water zone off the southwest Cape and the continued cooling of the
west coast waters is evident.
What's coming?
The present pattern, which continues
without visible interference, seems to favour the gradual inching in of
rainfall favourable conditions. That there can be possible interference cannot
be ignored, but the present assumption is that such interference would brief
and limited.
There should be a fairly broad band of alto
level moisture being fed southward and then south-eastward across the western
subcontinent. The outlook is that this band can vary in how far west would it
stretch and how far eastward could it retreat. From mid-week, a more positive
move seems to develop.
With the daily heating, convection currents
will be plenty. Occasional development can thrust such activity locally deep
into the upper air: the resultant thundercloud will produce some rain. Local
intensities could be surprising. But, as with this last week, many places will
see rain falling. Usually a few drops can reach the ground and with a
down-draught of air accompanying this rainfall attempt. A few places will,
hopefully, have figures to record.
The present rainfall detail reflects the
quite widespread range of the slight precipitation from the alto-levels, some 8
to 10000 above the surface, through the dry air beneath, at least.
This still October, the
likelihood of heavier falls is scarce on the record, so while hope may spring a
thermal, let rainy optimism bide its time.
|