Generally ‘heat wave’ conditions may occur in South India during May or in the first half of June or before the advance of the South-West monsoon. However, it can revive or resurface till June-end ever after advance of South-West monsoon over an area due to weak monsoon current due to absence of rain over land areas. South-West monsoon advances in pulses and its air movement and associated rainfall is also pulsatory in character. A fresh pulse of strong monsoon can suppress the hot spell.
“In hot weather season, hot dry winds from north or north westerly direction blow from north India over Andhra Pradesh. It results in significant rise in the maximum temperatures during May and in the first 10 days of June. A semi-permanent trough of low on sea-level chart extended from June 1 from Odisha to south interior Tamil Nadu across the Andhra coast,” says retired director of IMD Rama Rao.
The location of this trough blocked the inflow of moist wind from the Bay of Bengal. Calm or light winds prevail along the trough line and stations located on this line or close to it experience hot and sultry weather. This synoptic situation created a deleterious effect in the form of heat wave in the coastal areas before and after the onset of monsoon.
Visakhapatnam, Vizianagaram and Srikakulam districts are located to the right of the trough line. Occasionally, moisture is drawn into the trough from the south or south-easterly direction from the Bay and coastal areas experience thunder showers in the evening. Owing to thunderstorm people experience temporary relief for a few hours and the hot weather will roll back the next day.
