Westward-moving BSISO mode is likely to bring active monsoon conditions to the core monsoon regions during the next 10-20 days.

15-07-2024 | 9 AM

Current synoptic conditions:-

Monsoon trough is south of its normal position and extends up to lower tropospheric levels, it is likely to remain south of its normal position during the next 4-5 days.

The off-shore trough runs along south Gujarat-north Kerala coasts at mean sea level.

A low pressure area over Northwest & adjoining West central Bay of Bengal off south Odisha coast and extends up to 7.6 km above mean sea level, tilting southwestwards with height.

Analysis

It has been proved that, Intra Seasonal variability of Asian Summer Monsoon is dominated by BSISO (Boreal summer intraseasonal oscillation) and Intra seasonal oscillations (ISOs) significantly contribute to the variability and strength of rainfall associated with the Indian Summer Monsoon.

BSISO or MISO has two modes

1. 30-60 day northward propagating mode

2. 10-20 day westward/northwestward propagating mode

The 30-60 day mode is characterized by a northward propagation, while the 10-20 day mode is characterized by a westward propagation.

Below is the streamline analysis of 850 HPA, 15th July, we can see composite structure of 850 hpa wind and westward/Northwestward propagating vortices from west Pacific Ocean > South China Sea /maritime continent > Bay of Bengal > Indian subcontinent, which is evident of westward propagating high frequency mode.

The Madden Julian Oscillation (MJO) index is currently located in phase 5 with amplitude more than 1. It is likely to remain in the same phase for at least a week. Thus, MJO phase and amplitude is favourable for enhancement of convective activity over the Bay of Bengal.

By looking at the above parameters, enhanced convection and formation of Low pressure systems are likely over a BOB during the next 10 days. Vortices will propagate nearly westward or WNW through central India along and embedded in the Monsoon trough.

Under its influence, active monsoon conditions are very likely over core Monsoon regions during the next few days.

Gujarat:- Forecast 15 to 20 July.

Monsoon trough is expected to remain south of its normal position during the next 4�5 days.

LPA/associated UAC/trough or either of them likely to linger over NE Arabian Sea , Gujarat and adjoining areas during the forecast period.

Offshore trough is runs along south Gujarat to north Kerala coast and is expected to remain so during the period.

Under its influence,

Gujarat will receive widespread rainfall during 15th to 20th June. Most parts of Gujarat may receive moderate to heavy rainfall, whereas Heavy to extremely heavy rainfall is very likely to occur over some parts of the state. Some parts of South Gujarat and Suarahstra may get extremely heavy rainfall. Areas of extremely heavy rainfall may get as high as 300-400 mm.

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Note:- Follow below scale for rainfall intensity

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