No. IV-18.4 - (IMD), Pune

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between the moist easterlies and the dry air mass further north over the
northern and central India is clearly defined by dew points (surface and
upper air). There is also a perceptible discontinuity in minimum temperatures
corresponding to this moisture discontinuity.
v) Rainfall over south Peninsula is generally accompanied by thunder.
19. Weak northeast monsoon over south Peninsula
with pronounced northerly upper wind flow
- 10 November, 1971
19.1 We shall now discuss a typical synoptic situation when the northeast
monsoon was weak and there was little or no rain over the Peninsula, with dry
continental air prevailing over the area.
19.2 On the morning of 8th November 1971, an extended low pressure area lay
over the south and the adjoining central Bay of Bengal, with another feeble
"LOW" over the Laccadives (Fig. 19.1). There was no well-marked eastwest
trough across the south Peninsula connecting the two systems; as a result, the
wind flow over the Peninsula was generally northerly/northeasterly in the lower
and middle troposphere and this stream was also quite dry (Fig. 19.2). Weather
was, therefore, mainly dry over the south Peninsula except for isolated rain
in Tamil Nadu. However, satellite pictures indicated good clouding in the south
and central Bay of Bengal in association with the low pressure area there.
19.3 On the 9th. also, the two low pressure systems in the sea areas persisted
(Fig. 19.3). On account of the intensification of the high pressure cell
over the western parts of central India, the northerly flow of dry continental
air became well-marked over the south Peninsula (Fig. 19.4). At 300 mb the subwas
tropical ridge over Laccadives area and the south Peninsula, far to the
south of the normal position.
19.4 A space cross-section for 9th along the mean meridian of 78°E is shown
in Fig. 19.5.
It may be seen from this that the air was very dry with very
low dew points in the lower and middle tropospheres practically over the whole