MONSOON ONSET OVER KERALA

 

The guidelines are followed for declaring the onset of monsoon over Kerala.

 

1.     RAINFALL

 

CRITERIA:- If after 10th May, 60% of the available 14 stations enlisted, viz. Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kasargode and Mangalore report rainfall of 2.5 mm or more for two consecutive days, the onset over Kerala be declared on the 2nd day, provided the following criteria are also in concurrence.

 

2.     WIND FIELD

 

CRITERIA:-              Depth of westerlies should be maintained upto 600 hPa, in the box equator to Lat. 10šN and Long. 55 šE to 80šE. The zonal wind speed over the area bounded by Lat. 5-10šN, Long. 70-80šE should be of the order of 15 ? 20 Kts. at 925 hPa. The source of data can be RSMC wind analysis/satellite derived winds.

 

3.     OUTGOING LONGWAVE RADIATION (OLR)

 

CRITERIA:-              INSAT derived OLR value should be below 200 wm-2 in the box confined by Lat. 5-10šN and Long. 70- 75šE.

 

Northern Limit of Monsoon (NLM)

 

Southwest monsoon normally sets in over Kerala around 1st June. It advances northwards, usually in surges, and covers the entire country around 15th July. The NLM is the northern most limit of monsoon upto which it has advanced on any given day.