Forecast Outlook for the 2017 NE Monsoon Season Rainfall over South Peninsula, India 1

Climatology - NE Monsoon Rainfall Sub Division Season (Oct-Dec) Rainfall (in mm) Coefficient of Variation (CV) (%) Percent of Annual total (%) Tamil Nadu 438.2 31.5 47.92 Rayalaseema 219.2 37.8 31.04 Coastal Andhra Pradesh 327.4 38.7 31.97 South Interior Karnataka 209.6 38.4 20.57 Kerala 480.7 28.8 16.44 South Peninsula 332.1 25.3 29.88

Verification of 2016 OND Outlook for India

Some Climatological Features of NE Monsoon Rainfall

OND Rainfall Vs ENSO South Peninsula Tamil Nadu El Nino La Nina Rainfall Category El Nino LaNina Below Normal ( <89) 8(28%) 9(38%) Normal (>= 89 TO <=111) 10(34%) 11(46%) Above Normal (>111) 11(38%) 4(17%) El Nino La Nina Tamil Nadu Rainfall Category El Nino LaNina Below Normal ( <88) 6(21%) 10(42%) Normal (>= 88 TO <=112) 13(45%) 9(38%) Above Normal (>112) 10(34%) 5(21%)

LARGE SCALE INFLUENCES 2. INDIAN OCEAN DIPOLE (IOD) SST anomalies are shaded (red color is for warm anomalies and blue is for cold). White patches indicate increased convective activities and arrows indicate anomalous wind directions during IOD events.

LARGE SCALE INFLUENCES 2. INDIAN OCEAN DIPOLE (IOD) Western Block Eastern Block IOD: SST(Western Block)-SST(Eastern Block) +ve IOD good NEM activity -ve IOD suppressed NEM Kripalani and Pankajkumar, 2004

CYCLONES AND DEPRESSIONS – SEASONAL CLIMATOLOGY MAM JF OND – Many C&Ds cross coast over NEM area; Some recurve NE-wards JJAS Source: Cyclone eAtlas – IMD  www.rmcchennaieatlas.tn.nic.in

Tracks of tropical cyclones – El-Nino vs La-Nina El Nino (1970 onwards; 8 years – Nov-1972,77,82,87,91,94,97,2002) La Nina (1970 onwards; 6 years- Nov- 1970,73,75,88,98,2000) More northward moving cyclones that sweep away moisture from S to N latitudes leading to suppressed NEM activity over southern India More westward tracks; Good TC activity over AS.

NEM RAINFALL DUE TO CYCLONES AND DEPRESSIONS 11% of NEM seasonal rainfall variation is due to rainfall associated with passage of C&Ds When C&DS cross TN / AP coasts, good rainfall over NEM region except over extreme southern parts and SL. When C&Ds cross N or S of TN-AP coasts, poor rainfall over NEM region except over extreme southern parts and SL. (Geetha and Raj, 2014)

Statistical Prediction System for NEM Rainfall over South India & Tamil Nadu Geographical locations of the predictors used for 5-Parameter PCR model for south Peninsula Geographical locations of the predictors used for 4-Parameter model for Tamil Nadu.

Models used & Forecasts 5-P principal component regression (PCR) model for probabilistic forecast of NE monsoon rainfall over south Peninsula. Normal rainfall is most likely over south Peninsula A 4-P PCR Model for probabilistic forecast of NE monsoon rainfall over Tamil Nadu. Probabilities of all the tercile categories are close to climatological values with normal category having the highest probability. Category Rainfall Range (% of LPA) Forecast Probability (%) Below Normal <89 28 Normal 89 -111 39 Above Normal >111 34 Category Rainfall Range (% of LPA) Forecast Probability (%) Below Normal <88 30 Normal 88 -112 36 Above Normal >112 34 5/23/2018

Monsoon Mission CFS (MMCFS) South Peninsula Initial Condition pertaining To Skill score of (1981-2008) C.C Forecast for 2017 (% of LPA) July -0.43 7.0 August -0.10 10 September -0.06 Tamil Nadu Initial Condition pertaining To Skill score of (1981-2008) C.C Forecast for 2017 (% of LPA) July -0.21 -9 August 0.21 2 September 0.10 3

MME Forecast from Other Centers

Temperature Forecast

MMCFS T2mForecast: OND 2017 Normal to Above normal temperatures most parts of the country

NCEP CFS2 T2m Forecast Below normal to normal temperatures along the Himalayas and over southeast Peninsular India. Above normal temperatures over the remaining areas

Cyclogenisis in North Indian Ocean S.No Classification of Cyclonic activity Criterion 1. Below Normal CA No. of CD days: less than10 2. Normal CA No. of CD days: 10-16 3. Above Normal CA No. of CD days: greater than16 The atmospheric parameters considered as predictors (Source RMC, Chennai) Based on MR and PCR (deterministic and probabilistic) model inputs, cyclonic activity (in terms of number of days of cyclonic disturbance) over the North Indian Ocean during October-December 2017 is expected to be Normal (10-16 CD days). S.N Parameter Region Period CC with CD days (OND) 1 Outgoing Longwave Radiation (OLR) 90-110˚E &7.5-12.5˚S July-Aug -0.62** 2 Zonal wind at 850hPa (U850) 80-90˚E &10-15˚N -0.53** 3 Zonal wind at 500hPa (U500) 95-105˚E &5-10˚N -0.51** 4 Zonal wind at 200hPa (U200) 20-50˚E &Eq-10˚S -0.54** 5 Meridional wind at 850hPa (V850) 110-120˚E &10-15˚S -0.60** 6 Meridional wind at 500hPa (V500) 75-80˚E &10-20˚N +0.53** 7 Meridional wind at 200hPa (V200a) 130-140˚E &25-30˚N -0.55** 8 Meridional wind at 200hPa (V200b) 95-100˚E &5-10˚N +0.48**

Summary of 2017 NE Monsoon Rainfall over India IMD operational forecast for the 2017 North-east monsoon season (October-December) rainfall over south Peninsula (Tamil Nadu, Coastal Andhra Pradesh, Rayalaseema, Kerala and South Interior Karnataka) is most likely to be normal (89% -111% of LPA). The long period average (LPA) of the North-east monsoon season rainfall over the south Peninsula for the base period 1951-2000 is 332.1mm. The 2017 North-east monsoon season rainfall over Tamil Nadu is most likely to be normal (88%-112% of LPA). The long period average (LPA) of the North-east monsoon season rainfall over the Tamil Nadu for the base period 1951-2000 is 438.2mm. The mean 2m temperatures over most parts of the country is likely to be normal to above normal.

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