NORMS USED BY METD WEATHER TO DECLARE SOUTH WEST MONSOON

METD WEATHER

AKSHAY DEORAS

SEVERE WEATHER FORECASTER

NORMS FOR THE ONSET OF MONSOON-

EVERY YEAR,METD WEATHER FORECASTS THE SOUTH-WEST MONSOON FOR INDIA AND THE ONSET DATES AND THE CONSIDERED DATES ARE POSTED OR MARKED ON THE BASIS OF FOLLOWING CONDITIONS-

MONSOON ONSET CONDITIONS AS CONSIDERED BY METD WEATHER

1] PRE-MONSOON SHOWER-

THE RAIN SHOWER/SHOWERS ARRIVING FROM 15 DAYS PRIOR TO MONSOON RAINFALL ARE CONSIDERED AS PRE- MONSOON SHOWER.

ANNUALLY FOR NAGPUR,METD WEATHER ESTIMATES 3-4 SUCH PHASES

2] MONSOON

A) - HEAVY RAINS

THE MONSOON RAINFALL OR THE ONSET OF MONSOON IS CONSIDERED ON THAT DAY WHEN THERE ARE HEAVY RAINS ( *** NOT APPLICABLE FOR RAINFALL DUE TO ANY CYCLONE LANDFALL***).

RAINFALL ACCUMULATION MUST BE MORE THAN 5mm

*** CONVECTIVE RAIN AFTER SUNNY MORNING SHALL NOT BE CONSIDERED AS MONSOON RAINS***

B)- WINDS

THE WINDS ( SURFACE-500MB) MUST BE FROM SOUTH-WEST ATLEAST FOR 48HRS AND HAVING INTENSITY OF MORE THAN 10KT IN ALL LEVEL.

( WINDS FROM SOUTHWEST FOR A DAY ARE NOT TO BE CONSIDERED AS MONSOON WINDS)

C) MOISTURE

***SURFACE RELATIVE HUMIDITY MUST BE GREATER THAN 60% ATLEAST FOR 48HRS

*** THERE MUST BE A DEEP LAYER MOISTURE IN ATMOSPHERE IN LAYERS 500MB-900MB ATLEAST FOR 48HRS WITH SATURATION ***

D) AIR PRESSURE

*** SURFACE AIR PRESSURE IN A REGION ( NOT APPLICABLE FOR HILLY REGION) SHALL BE BELOW 1006 MB CONSECUTIVELY FOR 2-3 DAYS. SINCE LESS PRESSURE REGION INDICATES LOCALITY OF THE MONSOON TROUGH.

*** ANY PERIOD WHEN SURFACE AIR PRESSURE GOES ABOVE THE LIMIT SHALL NOT BE CONSIDERED FOR MONSOON ONSET***

E) TEMPERATURE

*** SURFACE AIR TEMPERATURE MUST DROP TO 35C OR BELOW AFTER PRECIPITATION

*** TEMPERATURE SHALL BE MAINTAINED IN THE MAXIMUM LIMIT AS 35C ( MAX TEMP) ATLEAST FOR 48-72HRS.

*** TEMPERATURE ABOVE THE LIMIT SHALL NOT BE CONSIDERED FOR MONSOON ONSET***

F) CLOUDING

*** DUE TO DEEP LAYER MOISTURE,CLOUDING SHALL BE PRESENT IN THE REGION

*** OVERCAST CONDITION ATLEAST FOR 24HRS CONTINUOUSLY

ANY CLEAR WEATHER DAY WITH ALL THE ABOVE CONDITION POSITIVE ( EXCLUDING RAINFALL) SHALL NOT BE CONSIDERED FOR MONSOON ONSET

G) 850MB MOISTURE TRACK FOR NORTHERN LIMITS OF MONSOON

THE NORTHERN LIMITS OF MONSOON SHALL BE ADVANCED ONLY WHEN 850MB MAP SHOWS MOISTURE OF RELATIVE HUMIDITY GREATER THAN 60% AND BEING MAINTAINED FOR 2-3 DAYS

THE ABOVE ARE THE CONDITIONS WHICH METD WEATHER HAS BEEN CONSIDERING SINCE LAST 2 YEARS AND REGARD AS THE CORRECT MEASURES TO DETERMINE MONSOON ONSET.

THE INDIAN METEOROLOGICAL DEPT NORMS ARE DIFFERENT AND HAVE NO CONNECTION TO THE DATES FORECASTED BY METD WEATHER

ALL THE ABOVE PARAMETERS MUST BE THERE FOR THE PERIOD CONSIDERED

ABSENCE OF EVEN ONE PARAMETER SHALL BE A BARRIER FOR DECLARATION ON THE MONSOON

- AKSHAY DEORAS