Cyclonic storms and severe cyclonic storms form during October month generally cross the East coast of India. The storms in October month mainly form in South east bay and move into West central bay and then cross Andhra coast. These storms contribute heavy rains to the north of the system. A list of cyclonic storms from 1980, that crossed Andhra coast during October month and their rainfall contributions are as follows. They clearly indicate that Northern sector of the system gets heavy rainfall up to 200 to 300 km North of the center of the system compared to southern sectors where the rainfall amounts are meager.
1. In 1980 a severe cyclonic storm with a core of hurricane winds crossed Andhra coast north of Machilipatnam on 18 Th early morning. From the rainfall amounts in cm it is seen that during the period 17-19 th Srikakulam received 16, Vizianagaram received 17, Visakhapatnam 13, East Godavari 14, West Godavari 12, Krishna 7, Prakasam 7 and Nellore 3. So the northern districts received rainfalls more than 10cm with a maximum of 17 in Vizianagaram district that is about 300 KM from the center of the system.
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3. In 1982 a Severe Cyclonic storm over west central bay weakened into a depression and crossed coast near Kakinada at midnight of 16 Th October. The system weakened very rapidly in its final stage. Exceptionally heavy rainfall occurred to the north of the system with Waltair reporting 37 cm, kalingapatnam 34cm, and yellmanchili 22 cm.
4. In 1982 a severe cyclonic storm crossed South Andhra coast near Sriharikota between 1700 and 1800 hrs UTC of 18 Th. The cumulative rainfall in cm for the period 16-18 th october82 are as follows. Srikakulam 21, Vizianagaram 19, Visakhapatnam 20 East Godavari 4, West Godavari 3, Krishna 3, Guntur 2 Prakasam 2, and Nellore 3. So the district where the system crossed received only 3 cm rainfall where as the districts which are about 300 to 500 km from the center of the system received about 20 cm rainfall.
- 4. In 1983 a Cyclonic storm crossed north of Visakhapatnam around 2000 hrs Utc of 3 rd October. The cumulative rainfall in cm for the period 3 to 5 october are Srikakulam 14, Vizianagaram 17, Visakhapatnaqm 22, East Godavari 11, West Godavari 12, Krishna 8 , Guntur 3 Prakasam 1 and Nellore 0.3.
The place i.e Viskhapatnam where the system crossed the coast received the maximum rainfall of 22 cm and again the northern districts received the 14 and 17 cm rainfall and decreased towards south to an amount less than 1cm
5.In 1985 a Cyclonic storm that was at 16.5 N and 84.5 E at 1200 utc of 10th weakened and close to Visakhapatnam at 0300 utc of 11 th. The cumulative rainfall for the period 10-12 was Srikakulam 6 cm, Vizianagaram 4 cm, Visakhapaatnam 8 cm, East Godavari 11 cm, west Godavari 12cm, Krishna 1 cm Guntur and Prakasam 2 each and Nellore 0.3 cm.
The rainfalls at East and West Godaavri districts indicate that northwest sector of the system received heavy rains when the system was intense and out at the sea. The sharp decrease in rainfall in southern sector from krishnadistrict is clearly seen from the rainfall amounts.
. 6.In 1987 a cyclonic storm crossed north of Ongole between 0100 and 0200 UTC of 16 th. The cumulative rainfall in cm in during the period 15-17 was Srikakulam 22, Vizianagaram 17, Visakhapatnam 18, East Godavari 12, West Godavari 8, Krishna 6, Guntur 7, Prakasam 12, and Nellore 4. The rainfall amounts clearly indicate that Prakasam where the system crossed coast received heavy rainfall and the extreme northern sector i.e Srikakulam vizianagaram and Visakhapatnam received the heavy amounts. Again the neighboring southern district i.e Nellore received considerably low amount.
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7.In 1987 in the month of November a Severe Cyclonic Storm crossed near Machilipatnam
On 13 th. The chief amounts of rainfall recorded at 0830 hrs IST of 13 in cm are as follows. Calingapatnam 10, Sompeta 10, Tekkali 10 (Srikakulam district) Cheepurupalli 10, (Vizianagaram district) Waltair 13, Visakhapatnam (Airport) 11, Yellamanchili 7, Paderu 6, (Visakhapatnam district) Kakinada 9, Prathipapadu 8, Rajhamundry 6 (East Godavaridistrict) Atchanta 11, Koderu 11, Narasapur 11, Bhimavaram 8, Eluru 6, Chintapalli 6, (West Godavari district) Machilipatnam 12, Nandigama 9, Gudivada 9, Avanigedda 10, Vijayawada 7, (Krishna district)Baptla 21, Sattenapalli 12, Tenali 15, (Guntur district) Ongole 10, Addanki 15, Podili 11, (Prakasam district) Kavali 5 (Nellore district). So, even in November, places that are about 300 km from the centre of the storm get heavy rainfalls and gale winds. Visakhapatnam reported about 35 to 45 knot wind from 0900 UTC to 1800 UTC of 12 th when the storm was about 350 km South west of Visakhapatnam
So, concluding that northern sector of the system getting heavy rainfall indicates that these are NE monsoon type. October is the transition month after South West monsoon resides, NE monsoon sets over Andhra coast and Tamilnadu coast. During October the monsoon trough or the equatorial trough comes down and it will be between 10 and 15 degrees latitude. Similarly the upper air trough also will be over ANDHRA AREA UPO 500 mb. The convergence between the easterlies and north lies will be on the northern sector of the system. So the northern sector experiences heavy rainfall like in SW monsoon where the sw sector experiences heavy rainfall. So the forecaster should issue the rainfall and gale winds warning keeping the fact that northern sector gets more adverse weather than the southern sector and accordingly the concerned districts are warned during the month of October.
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