No. IV-18.4 - (IMD), Pune

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country. Surface dew point temperatures were falling over the Peninsula where
the 24 hour changes were about -2°C to -6°C. The minimum temperatures were
generally below normal over the country, being 2°C-4°C below normal over south
Peninsula. Pressures also rose over the whole country during the previous
24 hrs and the departures were of the order of +2 mb to +3 mb (refer to the
auxiliary charts in Fig. 19.3). All these features indicated the prevalence
of dry winter type circulation over the country.
19.5 On the 10th, the low pressure area persisted over the southwest Bay
of Bengal with a somewhat westward movement, while the low over the Laccadives
area was weakening. There was a further fall in the dew points over central
and south India. The minimum temperatures also decreased further over the
whole of the Peninsula and they were 4°C to 5°C below normal in Andhra Pradesh
and 2°C to 4°C below normal over the rest of the Peninsula (Fig. 19.6). There
was little change in the wind flow pattern over the Peninsula in the lower
troposphere. Weather continued to be dry over the whole country.
19.6 The low pressure area over the Bay of Bengal moved further westwards
and became well-marked on the 11th, when it was over the southwest Bay of
Bengal off Sri Lanka (Fig. 19.7). Under the influence of this system, the
upper air flow changed to easterly over the south Peninsula in the lower and
middle troposphere (Fig. 19.8) and incursion of moisture took place into the
south Peninsula; correspondingly the dew point and minimum temperatures rose
over this area and the spell of dry weather was broken on the 12th.
19.7 The tephigrams of Bangalore and Visakhapatnam for 9th and Madras and
Trivandrum for 10th are given in Figs, 19.9 and 19.10 respectively. These show
very dry and stable air. Madras even shows an inversion between 900 mb and
800 mb and Visakhapatnam between 850 mb and 750 mb.
19.8 This sequence highlights the following points: